Technical Alchemy

Still around

2010-03-22T16:06:00.001-06:00

Well, I have my bamboo hardware for my custom Makerbot sitting in the basement at home. I'm hoping to get to it sometime soon, but I'm in the middle of some major house renovation right now. Patience... Anyway, more to come soon. If the Makerbot bamboo works well, I'll put it up on my Ponoko store for sale. Should clock in under $200 I think.

A simpler rangefinder?

2009-09-22T12:04:00.002-06:00

So, ages ago, the Seattle robotics people used an analog video camera and some timing with a peak detector to "read" a laser line's distance. People do this with webcams these days. But their system was one of the first and also low power. So, how could we duplicate this?

Modern digital cameraphone cameras are cheap (see Sparkfun). But they're color. You get 1/4 red, 1/4 blue, and 1/2 green pixels in your image. The color filter is definitely not user serviceable. You can get monochrome imagers, but finding the optics and keeping the cost down is difficult.

Step 1: optimize for your design choices! I'd start with a red line generator from my laser level as a test. However, green line generators (doubling your bandwidth requirements) are available now for $40.

http://www.z-bolt.com/green-laser-line-generator.html

Step 2: design your logic. The idea here is that we'd only clock in the sensor data we're interested in (be it red or green). We'd use a threshold function to trigger if this is "the line". For each trip, we'd want to capture the line number, pixel position in that line at the very least. For more accuracy, we'd want to capture the value that tripped the threshold. This would let us process the average in a program and determine if we're seeing a reflection.

This can be done either in separate programmable logic or in a PSOC3/5. Ideally you'd only have 1 or 2 pixels per line, but reality may change this. For a 1300x1040line camera, for instance, reading a 1 pixel tall line would take (2 bytes for line + 2 bytes for position + 1 byte for threshold) x 1040 = 5200 bytes of RAM, updated at 15Hz. Throughput therefore would be 78KBytes/s or 624kbit/s. I would not be surprised if it was 3-4x more, but synchronous averaging by the cpu should knock the data back down to a reasonable size. Depending on how the averaging works out, most data could be converted to a 5-8 byte per line data calculation (16-32 bit range, 2 byte line indicator, 1-2 byte time indicator), and real time streaming to a host processor via SPI, CAN, or another moderately fast bus is completely possible.

We'd want a 2 line state machine. It would control the timing of the logic depending on which scan line we're in (RG or GB). So this would take in the camera's logic. We'd use the VSYNC to reset all counters. HSYNC would toggle the state machine and increment a line counter. A second pixel counter would be run with the system. We'd need an 8x8 threshold variable.

Return to the Laser Rangefinder: PSoC to the rescue?

2009-09-15T22:12:00.002-06:00

Of note, I have done my first soldering on the RepRap electronics. I plan to continue on it tomorrow.

Anyway, I was looking at doing a laser rangefinder again, to see if it's more feasible. I think it is. I found some hardware that can do the signal mixing and generate a 1MHz wave and a 0.98MHz wave to allow for a 2KHz signal sensor. Now, to duplicate the low end (still $2400) laser scanners that have a 1024 point scan over 360 degrees at 10hz. So, if I crank up to 10MHz and 9.98MHz I get a 20khz signal. I can digitze that at about 40MHz, so my smallest theoretical step size is 7.5mm. To do better I either need to mix to a lower frequency and sacrifice update rate, or get a faster counter. I could switch processors to 80MHz instead. That would get me 3.75mm steps.

Now, I was hoping to make this whole thing programmable, so I could test different signals (say from 0.1 to 10MHz). This would require either expensive hardware or a lot of digital potentiometer. I looked at the PSoC originally, and it is what got me looking at how feasible this project is again. The example they had was only mixing a 10KHz and a 9KHz signal in a special way, far below my target frequency. It also took half the analog blocks to do one mix, and I'd need to do two. The CPU was also just not fast enough to replace the fast MCUs I've been looking at.

Then Cypress announced the new PSOC5 series. 80MHz ARM Cortex M8 core. 4 analog blocks that can make a 14MHz bandwidth downmixer with ONE block. 4 matched comparators. 24 digital blocks. CAN. Even USB. Integrated GNU C compiler. I think I might be able to make this work without extensive external parts. A laser driver output, a PIN photodiode and amplifier, and maybe a secondary clock source for assistance mixing. I think I might be able to fit everything else inside. We'll see when I get there.

There's several digital motor control blocks, too. I might be able to combine this chip with a low cost DC motor and encoder and a mirror and mirror the capabilities of that $2400 laser model at a fraction of the cost. And only need one chip for everything.

Reprap electronics order arrives

2009-05-22T21:03:00.004-06:00

My order of the Gen3 Reprap electronics arrived. Now I'll have to find the time to build the electronics, but I have to organize and reassemble my work area in the basement first...

Note: Cat not included

The UAVs are coming!

2009-05-07T23:25:00.002-06:00

So, I was poking around and ran across DIY drones again. When I first saw the site a year ago, I wasn't too impressed. My opinions have changed drastically. About $200 gets you an add-on autopilot for most small R/C aircraft (Ardupilot). Others have a direct cosine matrix that fuses IMU and GPS signals into a very stable position and attitude estimation of an airframe. More expensive hardware, of course ($400?). I keep seeing daughterboards for these, and this makes me wonder. While it's not ideal, what would happen if you used an IDG 2 axis gyro (x,y) and a more traditional gyro (z) to make a "flat" board? This would greatly reduce any mechanical misalignment or damage, and cut down on the board profile, too.

They're looking for suggestions for an Ardupilot PRO. They want to run dual Arduino CPUs on this. One CPU should be running a fail-safe program, and also an XBEE signal. The second can be running the current Ardupilot software. This would let the user create an XBEE based radio and completely ditch the need for an external standard receiver. I personally would figure out how to put TWO Xbee sockets onboard. One would be running 900MHz (40kbps) and carry critical data and the controller information, while the other would be a 2.4GHz data uplink (250kbps) for anything the Ardupilot or other add-on cards needed to send to a PC. This would allow either a dedicated 900Mhz signal for longer ranged manual control and emergency signalling, or a double failsafe for manual control with extra bandwidth to ride on for the standard 2.4GHz modules. Duplicate this down at the radio and you'd be set.

Technically, using something like Ardupilot shields, you could have one shield providing IMU, GPS, and servo support, and another shield providing transmitter buttons, analog sticks, a display, and an FTDI or other chip based USB uplink to the computer.


IO Type______Aircraft_______Transceiver
Analog_______Gryo/Accel_____Sticks
Digital______Servos (PWM)___Buttons
SPI__________Gyro/Accel_____Display
UART_________GPS____________FTDI USB

Finally a powerful camera module!

2009-04-23T20:11:00.002-06:00

I've been looking at the CMUCam3 for a while, but I've never been very happy with the limited processing power of prior modules. Now the Surveyor comes out with almost exactly what I was looking for. Fast, enough space, can do video compression, or more importantly video analysis to run many image codes onboard. It might take more power than the CMUCam, but not much, nor much larger. And it costs less.

Ardupilot

2009-04-21T20:32:00.002-06:00

Was reading notes on Sparkfun's web site, ran across notes and work on the Ardupilot. Looks like a complete, but basic UAV is around $500 if you have nothing to start with.

Mass Memory?

2009-01-21T16:44:00.002-06:00

Just ran across Microchip's latest toy, a serial SRAM. I haven't looked at this class much as many didn't have a lot of memory, or were slow. This can do 20MHz SPI, not too bad, but still FAR short of the internal RAM speeds. What could we do, though?

Each memory chip can use a Chip Select, Hold, and standard 3 wire SPI. We can gang the chip select, hold, and serial clock together from each chip. It doesn't look like there's a problem twinning the serial in and out lines together for each chip. what we can do then is get a somewhat inefficient parallel RAM module then, starting at 256Kbytes. Might be useful if you have large blocks of data to transfer and can take some lag at the start and stops. You could talk to this array via a parallel port interface on an MCU, but instead of sending a single 24 bit numeric array for a read, you'd have to multiplex this out to all the IO lines. A little more processing, but probably still much faster than anything else. It's this command addressing that will slow it down the most, but it will work very well for sequential read/writes with, perhaps, less cost than a SRAM of similar price and without worrying about FLASH wearout.

PC Building

2008-12-30T01:14:00.002-06:00

Well, my wife asked me to build a PC for her for her prethesis/thesis work. Needs to run Autodesk Revit 2009 and Photoshop CS 2/3/4 as best as possible. We're sticking with Windows XP. Things I've found out so far:

1) Photoshop likes 1 or 2 cores, and a fast scratch disk
2) Hardware RAID5 for the main OS partition may be nice but is a real no-no if you want to migrate hardware in the future.
3) Revit 2009 will use up to 4GB in Vista (3GB in Windows XP) and one core for design work. Rendering, however, will use up to four cores.

So, this is what I'm looking at

Case: Antec Sonata III with 500W PSU
Hard Drives: 2x 1 TB Western Digital Caviar Black plus 1x 150GB Velociraptor
ROM: Any decent DVD burner (no bluray)
Video: ATI FirePro V3750 256MB
Display: still looking, probably a 24" LCD

Now, I haven't detailed my motherboard/cpu/ram choices yet. I'm going to have to determine how I want to tackle this:

Option 1a:
4GB (2x2GB) DDR3 1333 (~$100)
Core2 Duo 3.33GHz (~ $270)
MSI P45-8D LGA 775 Intel P45 ATX Intel Motherboard (~ $150)

Option 1b:
Substitute Core2 Quad 2.86 GHz (~$320)

Option 2:
6GB (3x2GB) DDR3 1333 (~$150)
Core i7 920 2.66GHz Quad Core (~$300)
GIGABYTE GA-EX58-UD5 LGA 1366 Intel X58 ATX Intel Motherboard (~$300)

Cost goes up and you go down the list. Option 1a is good but may be limiting in the future. Option 1b is more future proof but still not the newest technology. Option 2 is the bottom of the newest tech, which has too much RAM for XP, but I want to try to get the triple width memory controller working and it has somewhere to go with a future upgrade. It's somewhat slower, though, on single threaded applications. It's also the bottom of the pile for the processors.

Does Windows XP 64bit have issues with 32 bit applications? This would make the 6GB of RAM worth it. $140 for XPPro or XPPro64.

System layout is to put everything on a mirrored 1GB hard drive array. I originally wanted a RAID5 array, but I understand how bad that can be if you put your OS on that array. I'm not buying 5 hard drives to do that right now! The Velociraptor is for windows swap, Photoshop scratch, and general high speed mayhem. If I switch motherboards to something with an integrated SAS controller, I might swap out for a 15Krpm Fuji drive. Price is the almost the same incidentally.

The fish tank is on hold until the kitchen cabinetry is finished.

RepStrap/Mill combo?

2008-12-28T00:45:00.002-06:00

Looking around, found this:

http://www.thegeneralstores.com/37110.html

A stiff but glorified dremel tool. Good design and heritage though. Make a 3 axis CNC and attach an extruder head and off we go! Still researching this little 100W spindle machine though.

Linear motors: a little thought

2008-12-15T21:53:00.003-06:00

I was doing a little looking at linear motors. Got an idea that it would be a great replacement for the geartrain of a homemade airsoft or Nerf gun, plus I've always been looking at how to build them. I'm focusing on the tubular variety instead of the linear rail as I believe these will be easier to build with minimal components, but I suspect they're either harder to design or build with, as there are two major manufacturers making them, Copley Controls and California Linear Devices.

Construction notes:

First, I've been researching the shaft. From what I can tell, it looks like the magnets are placed end to end, NS-SN-NS and held together mechanically. I'm looking at using a stainless steel sleeve with a series of high energy rare earth cylinder magnets inside with spacers. Down the center will be a possible sleeve and a threaded rod. I'm not certain of the material yet. I'll need a jig to hold the magnets on the rod, then nut each end. I plan to custom cut some aluminum end blocks to suspend the magnets in the middle of the sleeve, and provide me with some semi-disposable ends to mount hardware to.

So far, if I build my first arrangement, I think I'll use this:

http://www.rare-earth-magnets.com/detail-ID-69.html

They're not the largest or the strongest grade, but this should keep the cost down, too. I'd like a higher strength and temperature grade, but I'd settle for a higher temp grade. Well, one thing at a time.

I've found both online and at my local American Science and Surplus good supplies of small gage magnet wire. I need bobbins to spin this on. Modern stators are often made of steel, but I'm considering building a modular "coreless" coil system to drive this. I might be able to build these as plastic bobbins to wind the coils around and possibly use to hold everything together. I'd probably still dip the coils in epoxy (probably thin fiberglass resin). I have a lot of research to do on this. The hope is to fit all this into an aluminum tube to protect, align, and provide a heat sink.

I also have to find and do some calculations to determine what power/drive I can do. I want to look at 12 or 24V power systems, not 180V DC buses (120VAC). Probably too dangerous. But this means high current, large conductor systems. I need a motor design guide for brushless motors.

I'll also have to have a module to hold the sinusoidal hall effect sensors. Still lots to look into, let alone building a drive module.

Cats

2008-12-09T23:11:00.003-06:00

No, not building a cat. My house now holds three (3) cats. two are bossy, one is incredibly pushy, and will eat the other cats' food. The one that's mine is a pushover and may not get all his food. My wife and I have been talking about a food dish control box using collar tags. I've been prototyping this a bit lately in my CAD program. It's simple and needs one or two switches and a small DC motor. End limit switches, a timer, and a safety slip-friction drive to the cover open and closed safely

Electronics wise I'm thinking an RFID system. Sparkfun sells some all-in-one readers that look to be easy to work with. I'm considering an ID-2 with a custom antenna wound around the base of the unit. Tie this to a simple PIC doing pattern matching. If it constantly sends out, keep the dish open until clear. If it only sends on initial read, close on wrong read. A simple H bridge. I could option in a Zigbee system if I wanted to track data on a PC somewhere.

10 months

2008-09-30T20:10:00.003-06:00

Eek, I got in over my head again. Getting a little time back finally. So, during my little break, a few things have happened. The wiimote is getting a 2 axis gyroscope addition. It's still only 5 axes, so close...

My wife has two half gallon fish tanks on the house wall. She hasn't had fish since she was a kid, and I never had. We've populated each with a single betta, but have been having ammonia spike issues with them. So, I'm working on a fail safe hidden filter tank in the adjoining room. I'll do a detailed writeup on this once I'm in the testing stages.

High Frequency RFmodule thoughts

2007-11-28T00:00:00.000-06:00

I've been interested in radar for so long. How do you get it to work at short range where you have nanoseconds to determine range? Well, I've been looking into what an RF module would be required to build a modular phased array setup. This has let me to believe how freaking expensive GHz class MMICs are. I've looked at Hittite's phase shifters. Analog and 4 to 6 bit digital. Nice parts... but somewhat out of my parts price range at around $100 each.

While I'd love to work on a 10GHz range design, I'm realizing that a 5GHz range unit is far more plausible with the advent of 802.11A/N and Wimax. Heck, TI's WLAN chipset might build the whole system at 2.4 and 5.2GHz with two chips and a few passives.

Research research research!

The Wiimote IMU

2007-11-27T15:20:00.001-06:00

I've always been interested in inertial measurement units. I recently looked at the Wii Zapper frame and thought that we now have a 5.5 axis IMU. The Wiimote has a 3 axis accelerometer. The nunchuck has another 3 axis accelerometer. Now, if you have six axes of accellerometers that are arranged right, you can get good rotational data from the accelerometers. Unfortunately, this isn't perfect in this setup. You get a good pitch and yaw, but no roll information. This can be estimated out when the unit is roughly at standstill by determining where gravity is. So, if you figure out your distance between the two accellerometers in the Zapper, you have a rigid 5 axis IMU with a wireless connection. No phystical hardware hacking required (other than maybe for measureing the actual center to center position of the accelerometers)

Pretty cool, no?

Wearable Displays: Some things never change

2007-10-20T10:25:00.000-06:00

You'd think that HMDs would change and get cheaper, even if they're not completely mainstream. Remember IO glasses? They're still around, and I don't think the price has dropped. My belief is that QVGA (320x240) is OK for a quick reference monocle design. VGA is the bare minimum for a useful one, and SVGA (800x600) is frankly the required minimum for people to accept a technology. XGA (1024x768) is the right resolution. People expect to achieve such resolution from their main monitors, after all.

If you look at two big HMD online stores, TekGear and VR Realities you'll see a lot of expensive hardware. Some of which has NOT been updated in YEARS. Disappointing, isn't it?

So, what have I found in my own searches recently? Well, 320x240 monochrome NTSC video monocles are cheap and easy to get. Some people are trying OLED HMDs, but they're just as expensive as the older Active Matrix LCDs. That example WAS under $1000, I wonder what happened to cause the price increase?

My personal bet for inexpensive high resolution HMDs come from the DLP and LCOS industries. Both technologies reflect light towards the display instead of blocking it like normal LCDs. DLP uses MEMS moving micromirrors. LCOS uses newer (cheaper?) specially processed silicon. The products from Headplay currently wins in terms of resolution for the price, plus it has oodles of inputs.

One thing I've noticed is how annoying these can be. Many are designed for total immersion. I don't always want that. I think Icuiti is on the right path for "mobile useable display".

Actually, what I'd love to have is a transparent (or Augmented Reality) display that can use my glasses for a screen and put up a simple monochrome image for me. A GPS map would be nice for instance. I'm not wanting a complete overlay, just a portable heads up display. Some systems are made almost like that, but I'm not willing to pay $200 for it, let alone $2000.

HMDs have one issue that's hard to measure. Comfort. Are they comfortable to wear? Am I going to want a bottle of excedrin sitting next to me after I use them for 15 minutes? Once the price comes down that people are willing to pay and you can get enough volume to get a few in stores, this will be a hard question to answer.

Solid machine design: CNC basics and options

2007-10-08T20:43:00.000-06:00

Been looking around at parts and pieces for a CNC machine. This structure works for whether the machine is for machining, sensing, or RepRap FDM. Your basic mill/machine will be a three axis machine. X-Y and Z. My preference for linking these machines together is to use the table on an in-out Y axis, then the main gantry left/right for the X axis on the cross member, and the milling head on a Z axis. Easier and capable of "reaching in" is if the milling head moves for Z. If the supports are moved, the mechanics are more complex (as you have to keep the two axes even) but the whole machine is stiffer.

Now, beyond the basic 3 axes, we can add more. One is doing both Z axes options. This lets you reach and achieve stiffness as need be. Rotary axes are the next useful axes. A worm gear based rotary table makes wide circular machining. A horizontal axis lets you work a lathe style mechanic into the system, but you'll need a driver and driven ends.

Many multi-axis systems start adding axes at the cutter instead. This is simpler from a mechanical aspect on larger machines, but always useful. Starting at the Z axis, putting on two more rotary axes to allow for machining withing a hemisphere, and can be very useful. However, a smaller or less forceful cutter is needed. However, you also need a very accurate motion system since you only have 180 or 360 degrees of motion, instead of, say, 1/16" of motion per rotation.

I'm considering a CNC cutter head. Around here, Menards has a low cost rotary tool with flex head. By mounting the flex tool, the cutter head can be kept small and light, allowing for good maneuverability on a small machine. Flat and ball mills can be used with 1/8" shanks, but I'm considering starting out with a carbide or high speed steel Dremel burs. These are more like small mill bits but have 12+ cuts. They also cut at dremel speeds (8000-25000rpm) which is well above what many mill bits are rated for. If a saw is needed, Dremel has some somewhat expensive but neat "EZ Lock" blades that make them quick change and indexable.

More thoughts...

Open Source Machine Controller

2007-09-29T19:28:00.000-06:00

I'm working my way through my machine controller system. 1 DSP, 4 motor boards, plus network for additional expansion.

I'm basing the design on some of the working theories of the motion controllers I've seen at work. I'm starting with PID synchronizing servos and some of the IO as a background priority PLC. Beyond this is the interfaces I'm hoping for.

Beyond my own programming interface, I want three different control interfaces. One, connect to the RepRap software package for doing FDM (maybe the Fab@Home software too). Two, G code for a lot of generic CNC and motion work. Three, an HPGL printer driver for doing generic 2D and 2.5D work. This would allow for very simple control of any 2D table style pen plotter printing system. With the right hardware, a router, laser, or anything else would be possible.

Back in the Saddle Again

2007-09-17T20:13:00.001-06:00

After a long, busy summer (time and money tend to disappear when you own a house!), I'm getting back to thinking on this monstrosity. I've been thinking on how I'm going to approach this, especially since I'm not certain as to the motor I'm going to use. So, current architecture redesign is as follows:

Comms/Power board: USB PIC18 on one side, bus powered. This does general housekeeping. Across the opto-isolated border, we have another PIC doing power management duties. This side has an ATX motherboard connector and power distribution/comm for CAN bus and distributing the 5V logic power out. The PIC is powered by the 5V/2A standby power from the PSU and monitors the PSU. I'm debating on either providing screw terminal power or using the drive connectors on the PSU. I've seen some PSUs have 25A of 12V power available. This does not scale linearly with PSU power, so I'm searching for the best unit for the job. I can't complain, though. under $20 for a PSU or around $100 for just a 12V industrial PSU. I'm planning on supplying 12V and 5V and 12V to all boards, plus a CAN chain. Not certain about the 3.3V right now.

This is being kept separate so I can swap out the board for an Ethernet board, or one that runs off a 12V car battery and generates its own 5V for the rest of the system.

Main Board: This is the other major change. I'm putting a good size DSP at the core (dspPIC33FJ256MC710 currently, although I'm debating a 32 bit ARM7). One quadrature and four SPI ports (on one bus, for absolute encoder chips) are available for motor feedback or other semi-remote sensor connections. A bank of generic inputs for limits, etc.

I'm going to put card edge connectors for PWM amplifiers in. Logic hides behind some buffers and a well capped 3.3V LDO. 4 slots, each gets 2 PWM, 4 control, 2 analog, SPI, and I2C routed to it. With some split power designs for the analog, I should get a fairly flexible setup. I've got plans to test out full and assembled H bridges from ST and Freescale, and also some half bridge implementations. 10A per board is my target. The high voltage bus will be brought in via screw terminals, as will the motor outs. This should protect the main board well. The vertically mounted boards will make it easy to fan cool the module. I can swap around modules to drive DC motors, brushless, steppers, whatever works with either specialized boards or up to four half H bridges. The I2C and SPI let me access chip monitoring on the cards. I can also put in IO cards if I need something similar. Still working on that.

I originally wanted to run all separate motor boards, but getting coordinated motion from that can be tricky. I also realize that multiple axes servo loop positioning and doing AC motor servo control will probably not work too well together. So, I've decided to go this route. I expect a 40 MIPs dsPIc or 60MIPS ARM to be able to control one stepper, one AC servo, or four DC servo motors without too much issue. After I verify that this works, then I can work towards remote motor servo loop control via the CAN interfaces.

I had originally wanted to make this a single board design, but I ran into the issue that I had both SPI busses accounted for (add-on cards and absolute encoders). While I can link into one while debugging, I don't think I want to make it my primary interface.

Most other boards (distribuated motor boards, etc) will stay the same.

Hydra: Mechanical head ideas

2007-05-17T13:46:00.000-06:00

Well, sitting here eating a late lunch, and I decide to ponder the major point of the Hydra variant. I want multiple heads and I don't want to pay for them.

The way I decided to do this is to have a rack along one or two sides depending on if you want single or dual head capability. Each head has a dovetail-like slot on it, with a stop at the top. One on each side of the head. One is the hanger for storage. The other is active slide with power and data spring contacts. The carriage trolley needs either a solid solenoid or a motor drive on it. To pick up a head, the appropriate (open) trolley slot drops. It rolls over to the head and aligns the slot and holder. Raising the slot engages the head. When the head hits the positive slot at the top, we are aligned and should have a repeatable position.

There are other ways to do it. This method needs constant power. Perhaps an "expanding" dovetail would hold the unit better and not need power or a brake to lock the head in place through power dips, but also would need another actuator.

The trolley head holders are not meant to run constantly, just when the heads are being replaced. If a fourth axis is needed, such as for milling or inspection, it should be integrated into the head. Same for the polymer pumps and other material supply methods. Looks like I'll have to get acquainted with CAD again.

RepRap Hydra: A real drive board

2007-05-16T22:11:00.000-06:00

Just a short note, looks from the datasheet that the MC34921 drive chip is transistor based. They only list voltage drops for the bridges. The package is rated at 2W dissipation, but the math makes me think it'll be pushing 9W if everything is on full blast. I'll still design the board around that, but it means I can't use it as a RepRap basic SBC.

I'm scaling back to a more basic DC drive (maybe make it a dual chip unit as a bipolar drive) and perhaps combining a MC33486 with dual IRFZ44ZS low side MOSFETs. This should let me drive 10A constant, and 35A intermittent. It's been on my list for a while for other motors. It's FAR bigger than RepRap needs, but this has several advantages. One, I have other projects that I meant a board like this for anyway. Two, this loosens the size requirements for RepRap servo drives, so they can get bigger (anyone want a 1m3 build area?). Three, the heat dissipation with smaller motors may alleviate any need for a heat sink.

Note to self: add links later, too tired right now.

RepRap Hydra: Drive...er... SBC?

2007-05-14T22:02:00.000-06:00

So, I decided to look at my previous post about H-bridges to start on V1 of my power board. Standard Reprap runs at 12V, with 1A/stepper roughly.

As this is my own, I decided to try the Freescale MC34921 first. I'm not afraid of surface mount, but this won't work for everyone. I might rebuild with discretes later. However, this does pose a VERY interesting result. I had picked the Freescale as it's fairly flexible, as I can drive DC motors and bipolar steppers with it with no hardware changes. It has high current limits (low heat for a lower amp setup) and current limiting (safety). I was planning one of these per axis so I could do microstepping or servo control. The third driver (2A DC motor or stepper) was just a bonus that would be used for some option switching... or so I thought.

I decided to pair this with a 3.3V dsPIC33FJ128MC706 (might change still, though). Same TQFP-64 10mmx10mm package. Perish the thought that I might mix up which chip goes with which pad! Four PWM generators. I was hoping to use something similar for a "universal driver" quad half-H board. This is close, but I can't uncouple the H bridges. I can, however, set up a PWM to all four (is it really four?) PWM inputs this way. I can even use another timer to provide another PWM output.

Added bonus, I have a 0.6A switching 5V PSU, a 2.5A switching 3.3V PSU, and a 1.5/1.8/2.5V 750mA LDO, all feeding off the same max power system (up to 38V, works fine at 12V).

Hmmm...

40MIPS, two 5A dc motor drivers, one 2A DC motor driver or unipolar stepper driver, one dedicated encoder interface, several spare serial interfaces. Add in the Austria Microsystems magnetic encoders (that I can't find who's using due to reprap.org being down) on the second SPI channel, and I think I MIGHT be able to make a single board servo based Darwin driver if it all doesn't spectacularly melt down on me.

I think I have some thermal calculations ahead of me.

RepRap: Homemade Engineering

2007-05-12T23:40:00.000-06:00

Sometimes bent steel and alumninum just don't cut it... especially when your mobile robot needs just too much torque to move well (per calculations). Oh well.

So, we depart on some DIY rapid prototyping to help shed weight. The RepRap project is trying to do just that. They have a ways to go, but they have working electronics and mechanics for soft plastic. I definitely can see them moving up to something more engineering grade, such as ABS or Polycarbonate, from CAPA (melts at 80C) and HDPE.

I've decided to embark on my own variant. The current design is very VERY good at what it does. I'm starting with a Darwin and working up.

Planned upgrades follow. Some will be in my Version 1.0 machine. I plan to call it the Hydra.

Electronics: My own design. Theirs is absolutely BRILLIANT to reduce complexity. I'm planning on using the USB-CAN controller I've been working on for communication. This may evolve into a USB-ETHERNET-CAN controller. Drives will be dsPICs. Extruder heads will be whatever I want, depending on complexity. CAN will be my backbone.

Power: I do like their use of an old AT power supply. If my motors don't take 12V, I'll be moving up to

Motors: I'm considering building my DSPIC drive boards as quad half H bridge units with encoder feedback. This would let me (possibly) parallel my connections to drive more load when I build a DC servo motor, move up to BLDC if I want to, and still stick with steppers if that's all I have available. If I do stick with steppers, I will be microstepping for accuracy.

Extruder Head: I'm expecting to have multiple extruder heads. They'll be hanging on a rack to the side. I'm looking into either an allthread or maybe pneumatic lift that's built into the main head. It'll have a dovetail design and be able to "hang up" the heads on the rack to swap. The CAN network will be terminated in the extruder head. I'm thinking that some decently heavy duty spring contacts for the main power (extruder motors, heaters, etc) and a set of four contacts for CAN. CAN supports hot-plugging electrically, so this should work.

Power Transfer: Belts work great. Although they may see some stretch issues. I know they moved to them for speed, but they're also running steppers. I might migrate the design back to precision allthread. For instance, to get 1 inch per second drive rates out of 20TPI allthread, you'd need to spin it at 1500RPM. This DOES concern me. Don't need to be smoking steel. I've looked at precision Acme screws, too expensive really, doubly so for any ballscrew arrangement. Standard acme screws aren't much more expensive than allthread, but they sound like they'll pull even more power than allthread due to the innaccuracies. Needs more research. I will start with a belt system, however.

Main frame: I'll start with the Darwin frame and modify it. I'd build a box around the unit for storage (and cat-proofing), and hopefully some protected runtime. I'd switch out the bottom board for some roughened aluminum plate. I'd mount a thermoelectric cooler under here with a fan. This would allow me to control build area temperature somewhat, which should aid in adhesion or cooling times, allowing faster building. One side will have to morph into my head "rack". I might also need some heater wire underneath, too, for when I need a warm plate.

It's all about communication

2007-04-07T09:56:00.000-06:00

There's a lot of different comm protocols out there in the world. Proprietary, complex, simple, you can find one to fit your needs. However, there's a few that are standardized and common. I'm doing a little groundwork study on what I'd want/need in a "comm hub". A single microcontroller board that provides me with various comms from my PC, so I can program or view whatever my project is spitting out.

Dedicated Interfaces.

USB: Great, now universal, relatively fast (most MUCs are 12Mb/s), provides up to 500mA of power at 5V. Cons, gotta connect directly to a PC. Integrated or UART bridge

Ethernet: Really universal, no fanout issues, can plug in anywhere with the right software/config. Now can do Power over Ethernet (but rare and might not be worth the hassle for me!). 10Mb/s is common for an MCU. Integrated or parrallel bridge or SPI bridge.

CAN: Not really universal, but simple wiring, I can follow my own design tastes, more bulletproof in implementation. Slower at 1Mb/s max. Integrated or SPI bridge.

The Asynchronous Croud, the U(S)ART users.

Asynchronous communication, perhaps the oldest in the book. Not necessarily robust, but can be made that way. Comes out of the MCU at TTL levels, and can be programed to match many of the following theme variations.

RS232: The old time PC comm favorite. 115Kbaud max to most PCs, although modern variations can go up to something like 921Kbaud. More difficult to deal with due to the +/-12V signalling. UART + level shifter. Point to point.

RS422/485: Not the same scheme, but similar electrical interface. Requires a single ended to differential converter, but works at 5V. Can be faster than RS232 or go much farther. RS422 is otherwise very similar, but can have some limited multidrop capabilities (1 master, 10 slave?). RS485 is a full addressed network setup with an 8 bit network design (256 nodes, usually limited to less by electrical integrity issues).

IRdA: Another UART user, but this time using a pulse width technique to encode the data in light packets. Both ends need to be aimed at each other, but it's great due to the electrical isolation. Lower speeds, normally maxing at 115Kbaud for embedded hardware, but much higher speed (and shorter ranged) variations exist.

LIN: The slower brother of CAN. Uses an ordinary UART and a single wire transciever set, so it's cheaper to implemen than CAN.

Board Level Communications.

A few very common serial systems are not meant to leave the board level, but that doesn't mean they don't.

I2C: Two wire clocked serial bus. One line for data, bidirectional, one line for clock from the master. Simple, a few different names (mostly depends on voltages, SMBus is the 3.3V name, I2C is 5V, Two Wire Interface is the name for those not wanting to pay Phillips for the patent I guess).

SPI: Perhaps the oldest bus in the book. This is a simple clocked bus with a master clock line, a master data line, and a slave data line. A master interrupt line and a slave select line are optional. Simple, not direction changes. Full duplex. Clocked so you don't need to worry about baud rate error. Takes more pins, though. It's fast, however, Microchip products can move at 10MHz (equalling or outstripping the high speed PC busses in general), I've seen some DSP chips clock out at 20MHz to 50MHz.

I'm throwing together ideas for a "communications board" that will encompass many of the above parts. I originally thought USB for the PC interface, but I'm now thinking ethernet as it's simpler to port TCP controls from one OS to another rather than USB drivers. CAN will be on the unit, as will be one external header (possibly with a level shifter?) for I2C and SPI (4 wire). The thing I run into right now is deciding what UART protocols to support. Most chips only have 2 async busses, and I probably won't be able to make the baud rates match exactly due to different clocking requirements. RS422/485 is a given for my needs. I'm also considering IRdA. RS232 would be nice, as would LIN. Straight TTL to the UART may be useful too, but I think it'll not be used too much (maybe a jumper/header block?).

Power Electronics: H Bridges

2007-03-25T19:42:00.000-06:00

And an Acrobat crash eats my post...

I'm working on deciding on a power stage to build first. My current target is DC brush motors due to the ease of use and availability.

The original target for my needs was the OpenServo project. Advantages? Small, proven, prebuilt drive train, already has basic position feedback and a motor. Disadvantages? I'd be tossing a control board, people do melt the casings from time to time or destroy the geartrain due to constant high stresses (Hitec 645MG), and I might be able to better put $40 to $60 of hardware per servo to better use. The Openservo uses either small discrete MOSFETs or integrated high-low FETS (IRF7309 (PDF)). These are small enough that the IO pins of a MCU can provide enough charge to get them to toggle at fast enough rates (25mA for a PIC, 40mA for the Atmel MEGA 168). If each FET is controlled by its own IO pin, you have maximum control of the system.

As FETs get bigger, the capacitive charge needed to switch them also grows. What happens if you don't have enough current to switch fast enough? One option is to use a small transistor as a current booster. Another option is to use a dedicated FET driver. Either of these will work perfectly fine and can allow you to handle much larger FETs. But they take space. The dedicated driver is used industrially, while the transistor is used for smaller FETs or as isolators.

What other options are there out there? Quite a few, but often times, they're no where near as good. Although single package drive parts are available, they often use more space or are harder to place than pairs or single FET chips. I've looked at several chips:

Freescale MC33887: 5 Amp full bridge

Freescale MC33486: 10A high side FETs with drivers for low side FETs.

Freescale MC34921: Mother of all printer chips. An analog encoder input (?), two 5A DC motor drives, and a 2A DC motor/Stepper motor driver. Plus a 3.3V linear and a 5V linear OR switcher regulator set. One chip.

ST VNH3SP30-E: Big single chip solution. Takes pulse and direction and can do 10A free air or 25A continuous with cooling.

Some of these chips have current monitoring built in. Some of these chips have various protections built in. What's missing? Control. If I'm lucky enough to have an active input for each direction, I usually get Motor direction A, motor direction B, brake to ground, brake to high. Great, yes, but what happens if I want to freewheel? What happens if I want to do some odd test that needs to have only one input grounded? I'm probably asking too much.

A lot of these packages are big, but they also handle higher currents and I don't need to design a motor board from scratch. I'm working on a motor test board that will have... one of these chips on it and various feedback methods so I can test different servo control methods, if I can find the right motors.

Ferret: Planning Detail

2007-02-24T22:08:00.000-06:00

As requested and so not to confuse people, these are the plan drawings of the Ferret, Copyright Dream Pod 9. They have scale indicators to show what the original scale is on them.

So, now we have a visual reference. To engage the wheels, the unit sits down on the rear wheel and slides the feet forward to about 30 degrees from vertical. I'm working out the kinematics and sizing to match my servo size targets.

Ferret is GO for Design!

2007-02-11T20:33:00.000-06:00

Well I've begun a project to give me a final target design. I blame the 1/6 scale RC paintball tanks for making me think about this. I started wondering "what if I make a Gear?"

For those who don't know me, Gears are humanoid one man IFV's from the game world of Heavy Gear from Dream Pod 9.

I did some scale calculations, and I'd be seeing 3 foot tall models if I went with 1/6 scale. So, I decided to target 1/12 scale (although this will be changed as I look at the realities of frame scaling) and pick one of the oddest designs available: the Ferret.

Ferrets are a cross between a walking robot and a motorcycle. Short and stubby, it has a large powered rear wheel that provides secondary locomotion when the front legs are locked together and the heel wheels are rotated down to provide a semi-tricycle arrangement.

So, what components do I see as part of this project?

-DSPServo design and standardization (Hitec 645MG and 805BB shall be my targets due to their high torque and good speeds)
-DC motor control (powered rear wheel)
-High amp switching power supply (based on a dsPIC design)
-Imaging
-Sonar
-Structural design
-IMU

I do plan to "arm" this thing too. I might make a four-part weapons layout. One scale-simulation armament plan based on IR LED (laser tag) hardware. Another may be based on low cost airsoft conversions. To play with the tanks, I might build a paintball bazooka. Last would be rockets based off my look-see into homebuilt Nerf weaponry. I can see a mix being good (rockets done in Nerf, cannons and lasers built around Lasertag and/or airsoft). Time will tell.

Given the specialized nature of this, I think I might have to break this off into another Blog once I have enough background down. Not everyone knows of Gears, of course.

Back to the drawing board...

CAN Bus designs - Servo and Power Supplies

2007-01-21T17:48:00.000-06:00

Over the last month I've been working on the hardware for my CAN enabled smart RC servo board. Due to space constraints, I've decided to make it a double board.

Common components are two 6 pin 0.1" headers with 0.6" spacing. The CPU board contains the CPU, CAN transciever, and a few power conditioniong components. I am currently trying to avoid needing a LDO onboard. A four pin (two power two signal) header provides access to the network. The power board contains the H bridge and related sensors (current, voltage, temperature). I'm still trying to decide where to stick the analog potentiometer. One pin header is 6 analog signals. The other header is the four PWM lines and a ground and 5V power supply to provide power to the sensors. There's also a pair of separate unregulated power lines to provide motor power.

To make the LDO-less idea feasible, I need an efficient and low noise power system available. While I have some good sized capacitors on the digital supply input pins, I may need to take a different approach if this doesn't work well. This is why I decided to work with a split board design instead of attempting to beat together a monoboard design, at least until I have the design proven out.

So, to power this system, I'm looking at a DC-DC converter. I've been checking out Microchip's SMPS hardware. I'd love to create a dsPIC based design, but I think that'll take more work than I want to right now, plus I need to do a lot of safety design then. So, I'm planning a SMPS based around a stand-alone TI chip, the TPS5430, with a supervisory and control PIC riding along side. The idea here is to provide a garaunteed 2A 5V supply with a 10mV output ripple. I hope to make each power module talk to the rest to allow for some load balancing, but I'm afraid of some sort of interference. 22AWG wire is rated for 2A continuous power, roughly. The supply can do 3A with a 4A burst. I'm thinking about making the CAN passthrough on the board have one side powered. I'm considering making some of my less space constrained designs having an input voltage monitor so I can feed information back to the monitoring PIC to allow it to adjust the 5V output to provide sufficient power to the entire CAN string. I just don't know enough yet.

It's actually quite funny that I've been finding the dsPICs to be equivalent cost to similarly equipped 18F chips. While I haven't been able to verify, given that I'm aiming for near-constant operation for a lot of these devices, I hope that running a much lower clocked dsPIC will pull less power than the 18F for moderate-math applications.

Because Mike Said So

2006-12-11T23:49:00.001-06:00

Technorati Profile

This is done for the uses of "claiming" this blog via Technorati. Does anyone even USE that thing?

Fun: Gunnplexer Radar Components

2006-12-11T22:35:00.000-06:00

So, what's available for radar components on the open market? Most radar guns (aka cheap hardware) is either in the 10GHz band or the 24GHz band. These high frequencies are also used by ham radio operators, so they sometimes try to use these as high bandwidth line of sight radio links.

So, where to get them?

IF you want new, expect to pay $500 to $1000 per node. Advanced Reciever is one that lets you know without requesting a quote.

How about used?

Well, depending on availability, you can assemble much of the parts you need from SHF Micro.

So, my friend Creuzer was wondering about interesting feedback effects versus police radar, so let's go over what you'd have to do. Police radar works purely on doppler effect. Gunnplexers use a pair of tuned diodes to produce a beat frequency from a continuous wave source, so speed is a simple conversion of output frequency to speed. Now, how do you play games with one?

If the police radar is "dumb" (common), the radar electronics will lock onto the most powerful signal. Because your return is FAR more powerful than his reflection, you should win this fight. Now, the tricky part. You'd have to take in his signal, determine the initial doppler shift from knowing your own speed, and then fire off the right frequency to add or subtract whatever you want to to that radar signal.

A "smart" radar system (does it even exist?) that looks for a specific strength return requires more time and investment. You'd have to apply something (like, say SHF's Eccosorb AN-73) that will reduce your radar profile. Of course, you also have to protect the usually expensive components, which would require a good dielectric (radar transparent) coating of plastic over the top. You might also need to apply a fine metal mesh to your windows to keep the RF from bouncing off your head and back to the gun (and then you can control the radiant direction more). Anyway,
you'd have to take a power measurement and try to radiate back a certain percent of that. This would also help with the "dumb" radar but it's far more expense than it's worth.

Sounds simple? Well, it might be, but there's an issue. Radar gunnplexers tend to "float" their tuning all over the place within a 3GHz band, and you usually only have 100MHz or so of available bandwidth. So, know your police radar bands and hope they have it tuned! Mind you, the old hardware worked at either X band (10.5 to 10.55GHz) or K Band (24.05 to 24.24GHz). Relatively more modern hardware runs somewhere between 34.2 and 35.2GHz. I've only found one reference to these, and it was from Japan and cost about $3000 per unit if my translation is right. 35GHz is becoming more common, though, I've seen a lot of miniature radar units (for UAVs) being built around hardware at this frequency.

And that is why I don't mind spilling this little tidbit. Unless your local police is using hardware from the 80's (they might be though!), you'll probably never be able to mess with their readings.

Fun Thoughts: Bad Drivers

2006-12-05T22:04:00.000-06:00

I've read several traffic related stories lately, mostly about the new tailgate detecting laser system deployed in Airzona. Interesting, but I thought of a far more interesting result.

Everyone seems to have a cartop cargo pod these days. How about we spruce one up?

First, bolt on a few fiberglass Sidewinder lookalikes. I'd probably modify them so you can point one forward and one behind. Add cones to the engine are to both disguise the fake-ness and help with the aerodynamics.

Second, put a couple of windows in the front and rear. Behind these put a surplus 10GHz or 24GHz Gunnplexer and horn (the core waveguide of most police radars) and a 905nm IR laser with optics to provide a flat cone (police laser radar). This will let you light up someone's life if they're the speedy paranoid type or the annoying tailgater. This will have no effect on those who don't have radar detectors. I'd probably have to add in an LED system in the missile "nosecones" that would pulse in time with the radar pulse. Wonder what people would notice and believe from the movies...

Now, add a custom "I support direct application of traffic law" bumper sticker and some fake (or real) vehicle battle scars, and you'll have yourself a winner.

Not a cheap project. Figure $50-100 per emitter, plus the cargo carrier plus the missiles and mounts. You'll probably end up spending $1000 on this toy in the end.

A lot of space will still be available. What to do with it?

Careful design would allow you to place an automotive PC plus a bunch of sensors up top. Hook up a lot of cameras and you could provide a 360 degree tour (plus traffic stops by curious cops!). You could also run an algorithm to track speeders and get actual speed from them (it'd take some additional circuitry on the gunnplexers). A dedicated computer controlled pan-tilt-zoom camera turret would let you get a REAL good photo of them, too. GPS would be an obvious addition, too.

Now, silly and probably (highly) illegal stuff. Drill out and place LOTS of RGB LEDs in the exterior. Almost invisible when off, you could give yourself whatever lights you'd want depending on the control program. Keep the top clear and put a plastic bubble on top with a fake (or real) radar antenna spinning in it. THAT would get some attention. Maybe you could claim it's a weather radar? I know some people would actually want the missiles on the side to shoot, but I cannot condone that, nor having a mine dropper in the back to bomb that tailgater with grenades/caltrops/deer carcasses.

Sensors: Ultrasonic Phased Array

2006-11-08T18:52:00.000-06:00

So, with the laser system falling through, I've been looking around at alternate distance measurements. Hence, ultrasonic. This isn't your typical sonar arrangement, though.

Your typical sonar system is composed of two ultrasonic transducers and associated electronics. One is used to transmit, one is used for recieve. Higher end units use one transducer (still figuring it out) and usually have closer range requirements. I'd like to build this one-transducer arrangement. Another issue/advantage to sonar is the wide detection spread. Some units can sense everything within a 90 degree cone, or so. Good if you're looking for ANYTHING, bad if you're looking for SOMETHING. Transducer frequency varies with size (smaller = tighter pattern). Some higher frequency ones (commonly 235KHz) have a much narrower cone, also.

I have a 25 KHz transducer, and might get my hands on a few 40KHz models. So, the pattern will be exceptionally wide. Cheap, though. So, how to counteract this? We turn to technology to do some cool effects?

Modern radar often times uses a phased array instead of mechanical means to slew the radar beam. A phased array is made up of many small radar units. These units have their signals carefully timed to generate specific phase relationships across the entire antenna. Due to the constructive/destructive nature of waves, this can be used to both combine the power of the antenna units and to focus the useful energy into a single beam. It also allows the unit to both be redundant and to electronically steer the beam path just by adjusting the phase from antenna to antenna.

Modern sonar also uses it, but in different ways. There may be a single sound source, but an array of recievers is used to detect the signal, allowing the arrival time and phase difference from each sensor to successfuly determine the direction and range (if active) of the target. This method is also used in modernday medical ultrasound to allow a 3D map to be generated from all the responses. We're looking at quite the DSP problem, though!

Considering I haven't found any hobbyist doing this, I thought it'd be nice to attempt to build a modular sonar array that can be configured to have any and all units be phase-related transmitters and recievers. I could control the whole thing via a CPLD, but my test unit will be based on a dsPIC probably.

The initial design will have single transducers (with associated filter and power electronics) placed on individual PCBs. Each PCB will have power, ground, digital in, digital out, analog in, analog out pins plus perhaps a serial port. The digital pins will allow a CPU to trigger and measure all recieved signals digitally, as most sonar units do. The analog pins will be there to let the user experiment with generating a cleaner analog frequency out and get the analog return. The transducers band-limit the signal, so the analog in may not be necessary. The analog out is more important as this could be coupled to a high speed ADC to allow more accurate phase measurements and to get certain signals out of the process (doppler shift, signal strength returns, etc). If some digitally programmed controls, like a digital pot, are used to control signal strength, a serial connection will also be supplied of the appropriate type. The individual boards have the advantage that you can reconfigure them to test out different transducer arrangements. They have the disadvantage of causing possible alignment difficulties that may result in bad results.

The CPU board would have headers for these boards. I could either generate the signals via PWM or output compare hardware. Returns would either go for input capture(CCP) or ADCs. Many dsPICs have a 500Ksps or 1Msps ADC with a 4 lane sample and hold system, allowing me to accurately measure 4 sensors at once. They also can have up to 8 PWMs and CCP units. In theory, this means that up to 4 analog signals or 8 digital signals could be processed at once. I think I'll start with 4 and go from there. I probably could do 8 analog signals at once at the speeds these ADCs work at without concern of being off too much (25Khz x8=200Khzx2=400Khz, so worst case is slightly better than the nyquist limit). Other architectures may be better for this (ARM people? AVR people?).

One idea for the mobile PC robot crowd is to use a 18F4550 PIC. These chips have a 200Ksps ADC and enough CCP units to possibly support a full 5 transducers. This data could be sent back on the USB bus for capture analysis inside a math program (I'm considering this myself for algorithm and hardware testing). After that, take what you've learned and put together a DSP algorithm for a dsPIC.

I think that this could result in quite exceptional sonar mapping with fairly low cost 1D, 2D, and 3D arrays.

Thoughts? Did I miss someone out there who's done this before?

Oops! The Laser Rangefinder

2006-11-01T17:20:00.000-06:00

Why you need to research before buying parts...

I meant to build a laser rangefinder (see paper that drove this idea here).

I'd like to get away from having to frequency adjust the laser, so I run across an Erbium rod for $10. Even if it's too damaged to work, I'm not out much. Now, my research into Erbium is that it's used in eye-safe lasers with a wavelength of 1.5um. Wonderful. It's on order and shipped as I type this.

Unfortunately, there's two types of Erbium doped rods. One is Erbium:Glass, with a pinkish color. This does the 1.5um lasing. Then there's Erbium:YAG. More expensive, it does 2.9um (half the frequency). It's greenish. See the link above? Yep, it's greenish. Unless they have a different color, I think I was shot down before I even started. There goes my "simple laser pulse". I also ordered several spare supposedly laser optics and several displosable flash units. Guess that means I'll have $20 or so in hardware sitting in my parts boxes for a while.

Now, depending on if the lasing rod lucks out in damage, I COULD try and get the rest of the parts, but I suspect it'd be cheaper for me to track down an Er:Glass rod than to get the frequency doubling crystal (KTP or KTA perhaps? I need a good laser handbook).

HMD: Where to get parts, what's new, what's soon

2006-11-01T13:13:00.000-06:00

I'm trying to head back to the land of the electronic for a while, with that, however...

I decided to poke my nose into head mounted displays. I've always wanted to have a small glasses or otherwise transparently mounted information display. Not all the time, but enough. With my service job, being able to display the readout of my DMM or oscilloscope directly into my vision would be absolutely fantastic.

So, what's available?

Let's start with the "near mortal" components.

Myvu

Ignore the marketing images, they don't do this product justice. This is perhaps the finest binocular HMD available. $400 is a bit steep for a QVGA display headset, but don't let the Star Trek visor design fool you. Micro Optical focuses on minimum occlusion display technology. That, translated, means it obscures as little of your vision as possible. This bar design allows you to see a lot above and below the displays, and the rest is actually tinted transparent, so you can see around the displays, too. The result? From the reviews I've read, it means you can actually wear them and use them without feeling any more strain on your eyes or stomach than a standard desktop LCD.

Apparently the design is rugged and lasts 6 hours on 3 AAA's (and the special IPod version runs on a custom lithium-ion in the special ipod case). The optics are a single fused block, so no worries about alignment.

3DVisor

Picking up where the original 3D headsets left off, 3DVisor is trying to bring high quality HMDs to a wider population. Yes, you do get the same disorientation issues as all enclosed HMDs provide. However, these aren't QVGA. These aren't VGA. Yes, they're full SVGA and have a VGA connector. Normally units of this resolution are $1000 to $2000. They're now selling this for $550. Rumor has it that they're going to be releasing an XGA (1024x768) model in the near future. Given that they were originally selling the current version for $900, the price break signals that both the OLED technology is maturing and that the future XGA model may break the $1000 barrier. XGA HMDs have been the realm of the military and research institutions and still traditionally cost as much if not more than a new car. I can't wait to see.

Now, parts

Kopin

I linked directly to their Cyberdisplay section. Kopin is behind many low cost HMD hardware designs. I wouldn't doubt many of their displays have shown up in the $200 bargain basement HMDs. I know their displays (black and white) have shown up in camera, kid's night vision, and currently kids nightvision on an R/C car.

Now, most of these were black and white components. While I love hacking, sometimes you have to start from scratch. And where does that get me? Kopin sells both the main components (LCD, backlight, driver chip) and prepackaged assemblies (monocle display, binocular displays) for QVGA and VGA. The QVGA monocle (no VGA version, though) interests me as a possible core component to building a HMD. No driver chip, so it's going to cost almost as much as the VGA binocular arrangement, but that's how things work. You get twice the product for half the price with HMDs.

And in the future?

Microvision

I ran across Microvision a year or so ago. At that time they were making high end HMDs for the military and had one $5000 red Nomad monocle. Sounds like a lot. They have a secret. They're the only group that I've seen that has an analog control 2D MEMS micromirror. I've seen the TI DLP hardware, that's pretty much a digital system, it's either pointing here, or pointing there. Microvision had used this to build the Nomad, and it let them put up any resolution they wanted to at extremely high framerates. Cost of the laser component and driver were the limiting factors. Apparently they've gotten over that. They're now working on integrating a fully working RGB laser MEMS projector system into things like car HUDs and cell phones. It's only a matter of time before the projector becomes available then. If it doesn't need any complex optics to work, this may be the best option to project an on-glass transparent HUD for a mobile user. The IPM looks quite small and hopefully inexpensive. Who knows, you might be able to pick up an XGA full color display for $100 at your local electronics shop in a year or two.

Algorithm: JPEG and related

2006-10-28T22:40:00.000-06:00

I've been researching image compression on and off for a while. I see the methods that make up JPEG forming a core standard that most modern image and video compression is based on.

I've been wanting to make a JPEG compressor in a dsPIC for a while now. What do you do when you only have 16K to 30K of RAM? You look at what you're doing!

JPEG takes a YCbCr image and compresses each channel separately. A block of 8x8 values is put through a discrete cosine transform (DCT) which, like the FFT, provides a frequency value. Next, there is a zig-zag pattern defined by JPEG that takes this 8x8 block and rearranges it into a linear 64 byte block. So far, if the DCT result is kept in a floating-point format, no data has been lost. Next up is quantization. Either a fixed multiplier sequence (simple) or one calculated from the overall image (complex) is used to scale the image data, losing resolution. After that, any data below a certain threshold is set to zero, which starts the compression. The final step is what's called Hufmann coding. It uses either a set or calculated table to assign a unique binary symbol (say 01 is one symble, and 011 is another symbol) to replace a part of data. The theory is that a symbol's length is inversely related to how often it shows up. Ideally the table should be generated beforehand from statistics, although on the fly table generation gets close. Both the Hufmann table and the quantization table need to be passed to the reader so that it may be effectively decoded.

It's a lot of information, but there are better and more in depth discussions on the net.

I have a camera that does VGA images. Standard output is 4:2:2 (I think that's the format). For every pixel, it puts out a greyscale 8 bit value and either a red or a blue 8 bit value.
So, I don't have to do any conversion. I can decimate the red and blue channels to bring it down to a 4:1:1 depth (4 greyscale per 1 of the color channels). To correctly capture this data, I need 8 lines stored in RAM. As a raw data count, that would be 10,240 bytes. After decimation that's 7,680 bytes. Might be a bit tight in there...

dsPICs have DMA, which makes it easy to get the data into buffers without CPU capture intervention. Since the 8x8 DCT is so common in image compression, people have been trying all SORTS of ways to get it fast and simple A single 8x8 DCT can be broken down into 16 1x8 DCTs. You run a DCT on each row, then one on each column. My plan is to run the DCT in place in the buffer on each row and put the results into a new buffer outside of DMA control. I can also sort the rows out to isolate the various channels at the same time. Once 8 rows have been read in for any channel buffer, the 1D column DCT can be run.

there are 40MHz TI DSPs that have DCT hardware for image processing, allowing them to do the rest of the compression in software. TI DSPs are great. I just don't want to fork over several grand for a compiler.

After that, I can immediately start making decisions. I don't necessarily need a full JPEG compatible image as long as I have a reader on the other end that can decode what I encode. One way suggested in a technical paper (find reference) is that the encoding stops at quantization and truncating the data. This is nearly as effective in compression as the Huffman table (both size and quality) and greatly reduces the additional workload required. High frequency information suffers greatly, however. I'm considering this method. given the extremely rapid data transfer that must be done for an embedded camera. I'd like to get a VGA or QVGA video compressed down small enough to stream over an RF link, but I believe that may be impossible given the horsepower I want to attempt it with. Time for a 200MHz ARM32?

Tools: CAD for the home user

2006-10-28T22:10:00.000-06:00

I've recently started looking for good, no cost CAD software to work on my solids designs. I wanted to find something that's anyone can get and use continuously, so no expensive packages or time limited demos.

My original hunt lead me to open source. From there, I ran into the following software. I'm still just touching on these right now, so I might be missing the big picture.

BRL-CAD

BRL-CAD is an open source implementation of the Army Ballistics Research Laboratory solid modeling package. They use it to do simulations of various combat scenarios. Its results look pretty, but the Windows package I looked at shows that this is going to be a command line driven uphill battle. It's essentially a collection of very powerful software bits that can read and work on the same data set.

openCASCADE

Another CAD package, although this is not based on a US DoD project. Seems similar in capability to BRL-CAD, and also may be command line based. What got me interested in looking at this one is that it has close ties to various finite element analysis software packages.

Blender3D

Ah, an old open source 3D modelling standby. While you can do solid CAD style modelling with it, and it has a much better UI for diving into it than the prior two, it doesn't appear to do solid modeling, which may cause issues if you want to post-process the component.

Now, there's also a few "freebie" packages I'm investigating. As they're based on commercial packages for Windows, they tend to be at least easier to dive into within a few minutes. I'll have to see how everything stacks up in the long run.

Solidedge 2D V19

Basically the 2D component of SolidEdge, this is a really REALLY nice free 2D CAD package. It's not AutoCAD, but it reminds me of the fast and simple CAD package I learned on back in high school. It's also nice that it can open and edit all AutoCAD files, and can export into AutoCAD and MicroStation formats, so it's not locking you into its format.

Alibre Design Express

I'm just going through the initial tutorial for this one. If it's up there in capability with SolidWorks and SolidEdge, this one's a keeper. They've removed the ability to work with sheet metal forms and the ability to generate bill of materials (these are usually addons in other programs anyway). However, it looks like it's all there, I'll give it a try and I'll have to follow up on this at some point in the future.

The Fourth Combat Form: Nerf

2006-10-23T23:31:00.000-06:00

As this blog's rolled on, I've talked a bit about three different combat teamplay concepts. MilesTAG (beefed up laser tag), paintball, and Airsoft. Well, to round out this, let's take a look at another obscure teamplay game, Nerf.

Most people (read kids, teenagers) get a few Nerf guns and play a few "shoot em" games with friends. A few go and modify their stock nerf guns to remove some of the safety limitations. A few others go and make their own cheap, custom rounds. Even fewer go and build their own guns, usually low shot PVC contraptions that, while ergonomic and effective (although sometimes really neither), they make a bullpup pneumatic potato launcher look sleek and sexy.

And then... there's a guy who goes by the pseudonym Boltsniper. I believe he's graduated with a mechanical engineering degree, like me. Unlike me, he exercises his 2nd amendment rights. He also uses that knowledge gained to make semi-automatic full custom Nerf designs that work.

I don't want to copy him, but I will learn from him. I still want to make that airsoft/paintball OICW. For that, I need to understand how shell load and eject systems work. Well, at least the loading system, as I've been contemplating a caseless design.

So, today's objectives?

Part 1: Figure out a caseless Nerf gun system that has a working magazine system and runs on 3/8" nano Stefan darts. 9.5mm caliber if true diameter.

Part 2: Take the magazine system and integrate it with an airsoft style motor driven plunger system. This will allow select fire and full auto to be implemented. I have no objection to Boltsniper's pump system at all. It's quite the marvel in terms of system understanding and parts availability. I just want to see if an airsoft style reciprocating assault rifle will work.

Project 2 will be scaling this up to 25mm for range tests and practicality testing on dummy airsoft airburst rounds.

And no, I haven't given up on MilesTAG2020. Frankly, the various systems all kinda melded together. My ultimate objective is a series of modules that connect together and can be used for various game types. MILES is just the "ultimate" use, as it will integrate the actual shot detection, scoring, and shooting into the module network. The problem is, like the real MILES, you can't simulate indirect fire or area effect attacks effectively. While not a big deal for a game system, the US Army's troops are not ready for the realities of full combat that includes shrapnel clouds. That realization was not mine originally, but belonged to some article I read. I fully agree with it, however.

Near field active target tracking

2006-10-21T23:24:00.000-06:00

Life got me. Busy summer, who knows if it's over yet...

I ran across a website a while ago about using a laser and photodiode to track a target in 3D.

http://www.k2.t.u-tokyo.ac.jp/fusion/LaserActiveTracking/

Now, they use a pair of galvanometers to control the laser. Nifty. You can build some yourself actually. It's mostly a magnet, glued to a shaft on bearings, over a magnetic coil. One end has a first surface mirror, the other has a feedback mechanism.

One issue with building galvanometers yourself is that you probably won't get anywhere NEAR the frequency response of a pro set. I know of a pro set for laser shows that runs $700 or so. That's less than half what most places would charge.

So, do we have alternatives? I believe yes. At the loss of flexibility and speed, we can probably use two standard RC servos for X-Y positioning. The high speed circle drawing could be replaced by a small motor with an off-kilter mirror. Now, to adjust circle size, either a small push rod to another servo-esque setup (worm gear?) or a different focusing mirror arrangement, I'll have to see what's pratical. A stripped laser pen diode should work fine for the source, and I can get a decently matched photodiode from Digikey et-al. Optics, motors, and other oddball stuff actually should be available locally for me at American Science and Surplus. Even the parts for a first run galvanometer if I so chose that route.

While the demonstrations they do are good, they have limitations. Power output and circle size is based upon relfected light from the target, and it's assumed to be roughly spherical. Makes adapting it to track other objects difficult. Not impossible. I'm more worried about tracking, say, my pasty white finger and then having one of my darker compatriots try it and the system thinking he's a meter farther back than he is. Time will tell. Maybe a slightly off-axis reciever running a 2D PSD (position sensitive device) would allow for rough triangulation and automatic tuning.

Blog Info

2006-06-30T20:56:00.000-06:00

To that handful that has wandered across this blog, it appears that when I tested moderation months ago, I didn't save the notification email. Well, I just found my backlog, cleaned out the ads, and published everything else. I've removed moderation for now and now have enabled image verification. We'll try this for a while. I think I need to setup some other notification to... wonder if there's an anonymous email form...

ITX

2006-06-30T20:21:00.000-06:00

Now, some of you are familiar with the Via Mini and Nano ITX boards. Nice boards running the Via C3/C7 series processors, 500MHz to 1.5GHz. Mini boards are 6x6 inches square and use "standard" PC components. Nano boards cost nearly twice as much and use laptop components. RAM prices for your desktop DDR2 and laptop SO-DIMM memory is about the same. I'd run the OS off a 4GB CF card connected to the IDE busses that are on both systems. Video is integrated. USB and firewire do also exist depending on the hardware setup. Some 3rd party variants have an expansion bus that can have cards added to give additonal serial ports, LAN ports, even a cardbus CF and PC card dual slot.

To make these things connectable as the core of my MILES2020 design, handling any 802.11g communication, doing video processing from a local camera, providing voice communication, possibly driving a HUD or other video display (wrist mounted map screen?). I planned a lot of this for individual microcontrollers, but some of that processing duty can be offset into an ITX system. Nano boards have a mini-PCI slot, mini have a standard PCI, so cards are available for both.

How to mount it? I figure middle of the back, within a molded case. A LION battery pack would be below it, in a similar protective housing and connected via a cable. A USB microcontroller would provide a link to a CAN bus. The hardwired ethernet connection provides a high bandwidth link to a camera module (maybe the MILES gun main MCU?) if used.

Any other ideas?

Thoughts?

Mobile Computing

2006-06-30T18:50:00.000-06:00

Mobile computing is one of those sticky subjects. Modern mobile computing runs around as cell phones and PDAs. Then there's the crazy people working on a "wearable comping" system that keeps them partially in a computer generated world at all times.

I'm not THAT crazy. I look more for something resembling military computing. There when you need it, mostly hidden when not. One thing that popped up recently is a tech outline of a wearable PC. See link here:

http://www.eurotech.it/main/news.asp?2M=75

Now, I've run across enough hardware to consider how to build one. A base board system would distribute controls as needed. The main CPU would be a Gumstix, with video breakout and some extra IO. I'm hoping they have a lot of breakout of the video and input hardware. This could be hooked into a 2.2" touchscreen TFT screen ($50 from Mouser). The base board also has built in audio connectors. A 400MHz Gumstix running Linux may be powerful enough to run a voice recognition software package, providing hands free access. A subsystem microcontroller would control stuff like LEDs, IO, touchscreen, etc. I'd probably integrate a pseudo-IMU so that motion may be used to do some control, such as a mouse. I might also wire in a glove or something to allow controlled clicking, or move the IMU to the back of the hand there (now there's an idea...)

Depending on size, a LION battery set can be hidden either behind the board or elsewhere (depending on ergonomics and design). Now, final design is that the casing could be made to look rather professional with a vac-formed casing.

Optical Tracking Idea Update

2006-06-29T20:48:00.000-06:00

Well, it's been a while. I was thinking again today about the optical tracking and how to reduce the need for speed. What did I come up with?

Take a CPLD and feed an IR filtered Kodak 580fps B&W camera into it. Use a microcontroller to clock the whole operation (I still think a dsPIC30/33 is a good choice). Within the CPLD, do a comparison on each IR pixel byte to a programed byte threshold fed in from the PIC. If matched or exceeded (whatever is easier), output to a latching port that feeds the dsPIC and trip an interrupt line. By feeding through the line and frame syncs, too, you can setup a signal delay match to the data line. Now, the big idea here is that the PIC keeps count on what pixel should be output (use a Timer module?) and records this and the value whenever the threshold is exceeded.

While a simpler system based around just passing a go/no go signal would work, I'd like to have the imaging data, too. This would allow some filters to be built that adjust the sensor threshold depending on brightness. Another technique could be used to determine if the data recieved is a false response due to reflection, etc. If you're using the ultimate output to just track a beacon like I'd do, you could use moving target filters to keep the area watched small.

The big advantage of this setup over a direct link is that you can significantly reduce the image processing requirements. Another one is that it's still fully possible to do full frame captures without any additional overhead or need to "switch off" a software comparison module.

A disadvantage of this method is that it tosses yet another IC onto a video board I am hoping to keep small.

Base Ideas: Optical Tracking

2006-05-06T20:53:00.000-06:00

Sometimes ideas just pop in. Here's one for a basic optical beacon tracker that can possibly operate over extended ranges.

An optical tube (possible zoom, definitely close to focused to "infinity") has an array of IR phototransitors/photodiodes at one end. The target has an IR beacon (IR transmitter, probably driven by a fixed rate PWM from a microcontroller). By either just tracking which transistors are on, or in a more advanced variant, how much energy each sensor "reads" from the target (or if too many see it), the direction that the assembly has to be turned can be calculated. Power levels help to determine the "zoom" of the optics (if fitted). The PWM'ed signal allows either a hardware or software filter to be constructed to look specifically for the PWM signal (similar to the carrier frequency used in IRDA)

Open Servo and Camera

2006-04-25T19:52:00.000-06:00

I just can't get a good PCB made for that camera socket. The one time I had something going, my last socket self destructed. Just can't get back in the saddle on that one...

Now, while I think on how to attack that again, I ran across OpenServo. Nice system. They're working on their second generation based on a mid range Atmel chip. Actually, this is fairly close to what I was planning for the CAN network. I was going to rebuild a high power/speed servo with a custom controller board and provide full servo functionality. Still going to, but I'll be overkilling it with a dsPIC.

Speaking of CAN, I'm STILL trying to work on the software stack for that.

Camera: A Sense of Scale

2006-03-01T15:36:00.000-06:00

Well, I recieved my camera. I had issues getting a good picture of both the camera and the LCD. That is 7.58mm.

I really can't get a sense of scale until I have it in my hand. And that is TINY. The socket is about the size of a grain of rice and has a pitch of 0.4mm. That means 0.2mm of pad, and 0.2mm of space. That's roughly 8 mils each, about as fine as a normal hobbyist board house (say Sparkfun's BatchPCB ) will do. Scary.

Anyway, I'm planning on giving this one a try with home etching and soldering. I doubt I'll be able to get it without the mask, given the fine pitch, but who knows, it might work if I can figure out a mask or find out that a masking marker will work (temperature dependent).

Sparkfun!

2006-02-23T22:14:00.000-06:00

Sparkfun Electronics is a great site I've been poking around at for a long time. Just wish I could afford some of it.

Current wishlist that others might be interested in:
-Single transducer sonar unit with decent signal filtering onboard. Looks really nice.
-Various GPS units up the wazoo with lots of antenna options.
-Fully functional cell phone modules. Talk about tempting to build your own!
-Speaking of phones, they have a contest going on currently to figure out the hardware for their surplus, undocumented cameras from the Samsung E700.
-(I already have these) Affordable hot air rework and soldering stations. Quite useful
-accelerometers and gyros, ranging from single units to full IMU's. They are actually required to NOT sell the chips loose, but this is a decent way to get into the projects.
-Magnetic sensors for compass navigation.

I'm most interested in a small GPS module, a 3 axis mag sensor, and the sonar unit. That's about $170 worth of parts, so I'm afraid I have to hold off for a LONG while.

Impact Mechanics

2006-02-18T22:54:00.000-06:00

One of my odder interests are impact and protection. Slashdot recently ran an article with someone advocating using basically a memory foam for hardening armor. Now, I don't have a sample of memory foam right now, but I've seen Silly Putty and high density water-corn starch concoctions flow and move at one time and act like steel at a different time. I think that professional systems for impact absorption (special sparring suits) use a Neoprene outer shell, EVA underlay and a high density memory foam core, and probably similar layering going out the other side.

Now, WHY am I suddenly interested in this?

I've always got my mind on using stuff I build or want to build. I often wander back to Airsoft or Paintball as test grounds and play fields. Paint ball especially can HURT, so people wear armor. Now, most is fairly hard, but what if a lighter weight, fully pliable material was possible? Because it's local hardening, it should give more warning that you've been hit while still keeping the impact down. I've had a line of balls fired down my midsection before, it knocked the breath out of me. I'd have loved to have an inch or two of soft armor between me and them. Airsoft, due to the lower delivered energy, doesn't need to worry about this unless 25mm canister rounds start flying.

CAN: Universal bus?

2006-02-16T21:40:00.000-06:00

Well, I'm still learning gEDA. Finally got it loaded on a PC that I actually use. I got in my head a slightly modified version of my RC CAN interface. Instead of using a CAN enabled RC controller, how about a CAN enabled smart digital motor? I could then control the PID and rate control, increase accuracy, and have more information and control. So, this board should be designed to interface with the mechanics of the standard RC servo and replace it. So, I'm considering the following capabilities (no particular order):

H bridge based motor control
Temperature measurement
Input voltage measurement
Module amperage measurement
Programmable potentiometer for maximum position measurement

The above would allow for shutdown of the unit before motor burnout, power efficiency calculations and power usage control. Each board would be designed and built and made to support as large a range of servos as possible, hopefully allowing wide ranging retrofit. Target manufacturer is currently Hitec, although if a low cost, good quality servo is found it will be considered.

Offboard support circuitry:

High current buck/boost controller: provides servos and modules with approximately 5V of regulated voltage, several amps of power (I hope). Keeps the electronics and servos electrically isolated from the main motor voltage spikes.

Now, onboard circuitry, preliminary part selections:

PIC18F2580 (Microchip, QFN): integrated CAN, smallest board space for a CAN chip
MCP1252-33x50 (Microchip, MSOP): Power regulator, will provide 5V 120mA for 2 to 5.5V input, may be replaced if a good alternative for 2.5V to 10V is found and also will phase out the buck/boost converter from some designs. Isolates electronics from servo voltage spikes.
MCP2551 (Microchip, SOIC): CAN voltage converter (Requires 5V)
MCP6S21 (Microchip, MSOP): PGA w/ SPI controls for measurement of the amperage via high side shunt, may need an external SPI delta sigma ADC
MCP42100 (Microchip, TSSOP): Dual Digital Potentiometer w/ SPI controls. Used to scale line voltage to monitor raw 5V/high voltage line level, tune the high and low voltages of the position capture circuit to maximize accuracy.
MCP9800 (Microchip, SOT): I2C temperature sensor, due to lower rate, may be software driven

Note: space constraints will limit what can be implemented. The minimum design will include the PIC, voltage regulator, and CAN chip.

Now, another objective is using the Kodak 9630 camera chip and building a camera around it. It needs a 10MHz clock and 3.3V of power (sounds perfect for the MCP1252 above!). I'd configure it with the outputs buffered to work with whatever the logic is of the host processor. What's so special?

8 bit B&W
126x98 pixels (approximately 12K of RAM required)
Single shot and video modes
10MHz SPI (~90FPS) or 10MHz 8 bit parallel (~580FPS), plus H sync and V sync pins
16 pin interface expected (8 data, 2 I2C, ground, voltage, Vsync, Hsync, clock out, reset). Reset is also tied to the Power Good input of the camera.
Possible variant: Replace the clock module with a crystal and PIC18, allow for slight variance in clock, some onboard processing, power control of an auto-focus/zoom lens onboard.

HUD thoughts part 2

2005-11-05T01:51:00.000-06:00

So, I've revisited the original thoughts on the HUD. I've been learning rotating machinery vibration analysis lately and it put the idea of a piezo driver in my head. This is probably similar to what drove the original Virtualboy 50hz vibrating mirror.

Vertical update is no problem, but the high kilohertz horizontal update requires some alternate ideas. There is a MEMs 2D galvometer mirror that's used in both military prototypes and in a civilian mechanic HUD design from Microvision. Interesting idea, but I fear the drive complexity and cost! Optics always need high accuracy positioning, which makes this project a bit more difficult. I've been considering attaching a first surface mirror to a standard piezo buzzer to attempt a more cost effective solution, but I need to get that hardware first. If it works, I'll be limited by the buzzer rate and how much annoyance I can stand (although placing it in an evacuated chamber might help with this issue, or getting an ultrasonic transducer). Another option is a multi-faceted edged mirror that can provide a rotary multi-Khz rate. This would probably be easier to sync with, but again it'd take accurate machining (16+ facets) and a high speed motor (12K+ rpm) depending onconfiguration, placing a small gyroscope near someone's face if head mounted. If a faceted tube can be designed, this might work well with a very small high speed motor, however.

Other ideas from the scratchpad: Direct AC coupled magnetic field driven vibrating mirror, using a 2nd hand DLP array from a projector,

I'm thinking of experimenting with either a high output laser or a small bank of collminating LEDs (say 8?) to provide a picture. I think the LED's will be a parrallel array, as setting up a line would only give each LED an extended off time, switching and light output per pixel will remain the same, requiring high end hardware. This arrangement will hopefully be a good tradeoff between a single galvo laser and the bulky LED bar.

For the semi-technical curious, a little bit of the basic design idea behind this:

I'm attacking this project as two separate optical components, one provides the "screen refresh", low frequency signal, the other provides the "line refresh" high frequency driver.

The screen refresh will hopefully provide a 30 fps update. Progressive scanning is the current objective. However, via flexible software design, we can cheat. Since a vibrating mirror has to go through the same arc twice in one cycle, a mirror vibrating at 15 hz can provide a 30fps update rate. My current goal is a 60fps update rate for active updates.

The line refresh is a LOT more annoying. I'm hoping to use an SPI or similar buffered serial interface to provide the pixel information to the imaging device (if it's a single laser). These top out at 10 Mbps.

The characteristics above relate together like this:

bps = h-pixel x v-pixel x bpp x fps
screen refresh = fps
horizontal line rate = v-pixel x fps

Example calculations:
800 pixels x 600 pixels x 1bpp (monochrome) x 20fps = 9.6Mbit/s
600 pixels x 20fps = 12Khz horizontal line rate

Note, 12Khz = 720K cycles per minute, FAR faster than even small gas turbines and anything spinning this fast is highly dangerous!

This is possible safely with a small piezo driver or with a high accuracy multifaceted mirror on a small electric motor. The greater the number of faces the lower the RPM, but also the mirror complexity skyrockets. The piezo driver would prove simpler, but garaunteeing its dynamics is a far more complex problem than timing a rotating element.

For standard screen types, the horizontal width of the screen is usually the larger value. This is an advantage as it keeps the line refresh rate lower. Another useful function is that, for a fixed bit rate feed, you can trade off vertical resolution for higher framerates. It'll usually be easier to vary the slow frame update mirror than the high speed (and probably resonant) line mirror. If you turn this on it's side, though, a variable width system is possible, which might be more desireable than a variable height design.

Of course, the above information does not include areas where the mirrors may be out of position or highly distorted. These will in effect reduce the maximum possible video bitrate of the system and necessitate both a synchronization method for the data flow and possible padding of the bitstream with dummy values during periods of distortion.

I'm currently planning to attempt a 1 bit 248x160 display at 10hz update rate as a proof of concept. This is approximately one thirtieth the maximum data rate of the dsPIC SPI architecture and will allow much fine tuning. This requires only a 5hz window update mirror and a 1600hz line update mirror, which can be built from a motor running at 8000rpm with a 12 sided mirror. This will not be head mounted initially. Due to the need for 4.9kbytes of RAM for a video buffer, I plan to use a larger dsPIC (8Kbytes, 20 MIPS) as the video driver. I also hope to use it's DSP functions to both ease code development and update control calculations, and possibly drive a simple vector video engine to greatly reduce the bitrate and calculations required by a master processor. But that's for later.

Four Month Update

2005-10-21T23:57:00.000-06:00

Due to being unsettled (moving, bought a house), I've had to put my projects on hold for a bit. Well, I'm back now.

New tools: Mini metal lathe. I can now form my mechanical components and get back to being an ME! Plans include components for my other projects below, and probably experiment with tool design. I'd actually love to build a CNC mill eventually, but I'll need a manual mill and lathe first. Halfway there.

Project Updates:
I'm refining ideas for the RC core to the hardware I have. I've got a few 2.4GHz point to point 250K/s or 1Mb/s transcievers that are simpler to control and will provide me with a good starting point in RF design. I'm still planning on having everything connect together via CAN bus. However, some designs have become easier as Microchip is now selling/sampling full speed 3.3V parts and is coming out with a wider array of 16 bit chips shortly.

New Projects:
IMU2: while I do have some gyros sitting around, I've recently ran across a paper about using accelerometers as an IMU, Active Tremor Compensation in Handheld Instrument for Microsurgery. While I've known about the theory for a while, what impresses me is that they've seen increased accuracy over common triple axis accelerometer-triple gyro configurations. I have a pair of Freescale MMA7260Q triple axis dynamically scaleable accelerometers I'm planning on building an "IMU Stick" with as an experiment. This should end up being smaller and lighter than any other IMU design, possibly allowing RC aircraft autopilots to shrink in size.

Air Cannon Launched Sensor Packages: I've always wanted to do this one. A 25mm bore aluminum barrel about 18" (460mm) long is used to launch (via CO2 or air pressure) a sensor package. The initial package will be sensor equipped to track various pieces of flight data. Useful sensors that may be deployed are for both search and rescue and laser tag games. Parachute deployed motion trackers, vibration and sound sensors, etc. The critical components of the design will be a concentric ring that will use a transformer effect to provide data to the microcontroller in the sensor package in barrel, non-contact. This will allow (with additional hardware) to sight a target zone, and have the electronics tell the operator where to aim to hit that target. Through controlled pressure and temperature in the expansion tank (Especially for CO2), muzzle velocity of the sensor package can be controlled. Various ways of triggering the descent parachute at the right time will be tested (timer, airspeed through air pressure sensors, etc).

Laser Rangefinder: Always wanted to build one. I've found information and effective hardware for the transmitter and reciever sensors. I've found a 25 year old schematic from an old TI optoelectronics book for a phase-difference rangefinder. With modern electronics, I can probably make a nice Time of Flight rangefinder work. This might be ideal, especially since a near IR diode was found on Digikey that has a CW output of 120mW, well above the safe range.

Parts to Buy for: Juicebox

2005-06-05T02:05:00.000-06:00

Just for general imagery, you can't beat an LCD. Now, I've been planning on using a 9 bit (512 color) Sony TFT LCD for my large HUD in the future, and general purpose LCD now. In the last few days the hackability of the Juicebox has come out to mass media. Most people are focusing on hacking it to provide mobile video players. I'd love to myself, but I've always been a DIY guy and I wanted a different approach. Hence, I look at what's available. 8 MB RAM in the version I have. the 22 pin PCB molex board may be nice for some of my own I/O work. The processor is useless as it's a bare chip encased in epoxy. Now, the screeen... 240x160 12 bit (4096 color) LCD. Might be the same molex connector as my Sony LCD. I got my Juicebox for $12.48, which is less than the Sony LCD. Other than refresh rate, this is looking to be perfect for my projects. It might even interface with the Epson LCD driver that I've spec'ed out for the Sony!

Also included in this is a 22 pin LCD Molex connector (the other 22 pin board goes to the expansion slot) that might also work with the Sony. My source for the LCD's sells those for $3 each.

Thought Experiment: HUD

2005-05-21T22:47:00.000-06:00

I was thinking about how to build a low cost, lightweight helmet mounted heads up display. Mono color, vector graphics. See through.

I happen to have some specially cut but scratched HUD glass sitting around here. Not to useful due to the scratches, but a good thought provoker. One common way to get a HUD working is to have a well backlit LCD or CRT at right angles to the glass. Problem? Size, you have to accomodate the entire LCD, which may be 2.7" or even 3.8" in common sizes. You can get color raster graphics then, but that's more distracting that I want. I'll just slide an LCD with focusing optics over my eye if I need that type of display. Professional units appear to use very VERY small monocrome LCDs with a high output backlight to provide such detail. Unfortunately, 320x240 or more preferrably VGA monitors of this size are expensive. A broken modern DV camcorder may be a better cheaper option off of Ebay for oneshot designs.

I happened upon the old Nintendo Virtual Boy a while ago. It cycled a 224 light LED bar in conjunction with a mirror. This provided vector graphics (in stereo) at 324 x 224? at 50Hz. It was disorienting to use, but I figure something similar providing "infinite depth of field" guide lines for highlighting and information providing would be better, especially since you can see out of the unit. Problem? I'd want 240 LED's. That's a LOT of space I'd have to fill in. Another issue is the complex circuitry. I'd need a high pinout FPGA to drive the LED's. I'd probably use a rotating octal mirror to provide scan lines instead of a vibrating mirror. This also gives the option of overlaying and syncing multiple color bars to provide RGB color graphics as cost permits.

I briefly considered a single LED with driven X-Y galvatrons (ala laser lightshow graphics) but those are highly limited in their flexibility and cost a bit. Also that would put vibration sensitive mechanisms on a mobile platform. I much prefer the spinning mirror of above since that only has to maintain speed and have an optical encoder onboard to provide timing characteristics.

Anyone else have any ideas? I'm looking for lightweight, low cost solutions. Camcorder eyepieces are a good option, but many of the older models I'd sacrifice use miniature CRT tubes. I do NOT want several kvolts on my head. Ebay Camcorder finding is very hit and miss, especially since I'd need two identical digital units to build each eye of the HMD.

CAN Module status update

2005-05-20T02:01:00.000-06:00

Working on learning Eagle still to get the Zigbee-CAN module designed. Currently breadboarding a 4 DOF (2 accel, 2 gyro) IMU for camera stabilization and head tracking. I'll probably also throw in a CAN-USB adapter, too, so I can build a CAN network debugger/programmer for all my toys.

Found a few nice things over at the Electronic Goldmine website. They reminded me that I have a 2.7" diagonal Sony LCD (240x160, 512 color) that would make a good forray into HMD/monocle design for very little, if I can design a good driver for it (I see dsPICs in my future). Other than a 9 bit interface, it'd be a bit hard to control without 38400x9bit memory... so I think driving this with dual port RAM and a CPLD front end might be the best bet for me. We will see.

They also have a 16 grayscale 320x240 touchscreen that would be a good match for a forearm mounted control system.

CANMOD - A CANbus module system

2005-05-02T10:10:00.000-06:00

Well, after some deliberation, I've gotten a bit of a grasp on the basic boards needed for my designs. All boards have a CAN interface:

Zigbee and digital I/O
Generic I/O with breakouts for specific interfaces (parrallel, UART, SPI, R/C?, Analog input)
Brushed motor and R/C servos
Brushless motor
Audio I/O
Video Input/analysis
Video output/LCD
High computation module (if needed)

Now, serial bus connections will be available for the basics. Some will just be a single digital connection. Many will be on several inches of dongle bundle so they may be separated from the controllers.

I/R input
I/R output
IRDA transciever (UART)
Flash config module (I2C)
Button/slider input
Single event touch sensors
Accelerometer 3 axis?

These should allow me to build anything from small to midsize robots to high performance R/C vehicles (still need more range for aircraft, though) to Laser Tag systems

TAG2020 Evolution

2005-03-25T03:11:00.000-06:00

I've been considering the TAG2020 system.

We're looking at major reuseable software components of:

IR TX
IR RX
LED muzzleflash
LED hit signaling
CANbus
802.15.4

Uses of the above:

Hit tracking
Weapons fire
Intelligent weapon linking to user
Remote intrusion sensors
Squad Area Network

The 2020 weapon is being redefined. We're reconfiguring them into several major parts.

IR LED Transmitter: CAN equipped microcontroller that's dedicated to IR transmission
Gun controller: Most likely also the IR LED Transmitter, manages the CAN network, integrated 802.15.4 transciever for linking to the larger network. May have an LCD and buttons or headers for low cost triggers and readouts. May also have a hot-swappable "side ID" for games that use user removeable modules to allow changing of sides.
Trigger module: Each trigger module is CAN networked to the Gun controller on a common bus. This allows multiple weapons to use one transmitter. Weapon types may be ordered by priority. The trigger module may be used as a weapon type controller to allow modular reconfiguration on the fly.
Reload bay: CAN networked bay that controls ammo feed. Has optocoupled links to ammo clips as used.

2020 Hit Sensors will either have CAN or CAN and 802.15.4. They will use the same substrate, just varying in equipped parts to allow for mass production. Bus power may be provided to reduce battery numbers.

2020 intrusion sensors will share a standard 802.15.4 interface. This may be merged with the Hit Sensor board and have specific sensors (acceleration, tripwire, etc) added on via daughterboard connection. CAN may be provided as an alternate long range option (at 20kbps 1km range)

2020 Base packs will be made to communicate with 2020 LCD/UI units. The LCD/UI units will be mostly dumb, acting as a detached wired/wireless link to the Base pack. Standard Base pack options:

Player ID
Statistics tracking
802.15.4 controller master
Hit sensor location tracking (for "realistic damage" games)
Automatic configuration
Basic hit detection (extra sensors not needed to play)
Expansion slots/headers (bussed?)

Basic game setup will be:

1 gun (1x IR Transmitter, 1x Gun Module, 1x Trigger, 1x reload bay)
1 Base pack (backpack, rear hit detection)
1 LCD/UI module
2 hit sensors (front torso hit detection), CAN interface.

Optional future Base pack modules:

DSP voice command
compressed digital voice communication
GPS/IMU position tracking
900MHz long range datalink
Camera tracking and targetting (shoulder mounted)

Modular Parts

2005-03-19T04:20:00.000-06:00

In the little time that I actually code and test the RC core, I've come up with a list of modules that it's running.

A to D conversion with reading to output transform
R/C servo control
2.4GHZ transciever
Brushed Motor Control
CAN network

Now, as I look at the MilesTAG2020 system, I have these modules:

A to D conversion
IR encoding
IR decoding
2.4GHz Zigbee transciever
CAN Network
Brushed motor control (feedback, cyclic operation)
R/C servo control (turrets, drive motors)
Human Interface design (LCD menus)

Although not initially intended to be used together, the RC core will become a stepping stone for the MILES2020 system. I suspect I might make a few target drones and recon UGV's eventually, maybe even put a turret on a UAV.

Now, I need a name that isn't TM the MilesTAG guys, but relates to being compatible...

Yet more projects?

2005-03-11T06:23:00.000-06:00

A lot of my projects are things for me to mess with, and many that are high speed logic need a few more intermediate projects thrown in before they should be attempted. So, I ran across a very cool project page.

http://www.lasertagparts.com/mtdesign.htm

I'm thinking of breadboarding their basic circuits for a little fun, then going for a high tech Zigbee upgrade. Every player would have a gun, a backpack, a helmet/hat, and a few other sensors. Many sensors would just be a Zigbee unit, LED's, an IR sensor, and a PIC for logic control. The gun would be similar to the designs above. The backpack would be used for radios and some high tech gadgets. The helmet may have a comm headset, but would otherwise be there for protection/team identification.

I'm considering giving it a larger LCD (2x16?) and using capacitive switches for user interface, keeping the box sealed and possibly a bit more watertight.

For another trick, a serial bidirectional optocoupled box would be used for a magazine. A simple pulse request for one round of ammo would be flashed to the box, it would respond with a pulse if it has one. I'd either put a battery inside with a switch to restart it, or use a very low speed loop wireless system to reset (like 125KHz). There would be microswitches to turn on/off the interface. If field reloads are possible, timing lockouts and a reload field back at base would be used. This would keep people from sitting in the reload area with infinite ammo. The interface itself would be small and universal, the changes in the box would be different for different weapons.

Hmmm... more later....

DSOs and Compilers

2005-03-04T14:22:00.000-06:00

Still finding time here and there that I feel I can code. So, some new things I've drummed up or run across.

Oscillopen

I still would like to build a DSO for my computer eventually. For this, I came up with a different method that may still be compatible with the original Bitscope. Instead of using a CPLD to feed SRAM data from a ADC, why not use a FIFO? TI sells a nice reconfigurable one that'll be useful for porting data anywhere from 8 to 16 bits wide into an 8 bit serial port on a PIC. The 64K/128K buffer is about the same as available on the bitscopes. I may configure it to have an 8 bit ADC and an 8 bit logic capture, or maybe a 12 or 16 bit ADC. I like both options, maybe I'll build both. I can run the FIFO up to 167MHz, far exceeding the capture rate of the Bitscope, but I lose the Bitscope's flexibility and mode triggers made available by the CPLD. Still might be a good project, especially since I don't have to run it at 167MHz. A USB PIC can live on the output end of the FIFO to provide a USB control and transfer interface to a PC. If I build it with a slower 16 bit ADC, I might consider using a dsPIC and doing a live digital filter or micro-based SRAM transfer instead.

As for Oscillopen? I'd like to try to fit it all into the format of a fat marker, and either make it battery powered or a USB port on the far end with either a single BNC or similar connector on the input end.

Free Compiler

Wll, Microchip's at it again. They've released their C18 C compiler for the 18F series for free now. Sorta. It's the student edition. It will stop being it's most optimized after 60 days IIRC, however, it will continue to work. Win win situation for hobbyists in my opinion. If you need better speed and smaller code, go assembly. I still plan to code my R/C core in assembly first, as a learning experience.

Random electronics

2005-02-04T18:14:00.000-06:00

Time flies when things go wrong. However, on a few good notes...

FPGA's
I've pretty much settled on trying to get Actel's ProASIC-3E starter board. List price for the lighter weight version is $250 (due in quantities 2Q 2005). What I do like about it is that it includes a Libero GOLD license, which is all I really want. That's worth twice the dev kit costs. They're highly rad tollerant, so good if I ever decide to send up high altitude balloon sensors. Just no dedicated hardware DSP features (Multipliers, MACs, etc). Still might be cheaper to implement myself given how cheap the chips supposedly are.

Now, second on the list is Lattice Semiconductor. Similar issues, but I like their low cost LatticeECP for DSP route (same or better hardware as the big Stratix and Virtex parts from the top vendors). IF I decide I need DSP that badly, I might chase them down. Too bad their expensive dev kit hardware and 6 month free trial don't really cut it for me. I don't want to drop 2K on something that I might use a handful of chips my entire hobby career. I hate it when my software expenses outweigh my hardware. I'll probably end up turning back to Xilinx's Spartan3 or Altera CycloneII eventually, given better "free" software (both support, licensing, and specialized IP availability) for complex hardware support (video DSP, etc). It's a balancing act.

Circuit Cellar Contest
Well, I got my Renesas contest hardware from CC. 32 bit CISC microcontroller with a CAN port. Should prove fun if I need higher hardware speeds for my work (probably only if I start doing on the fly IK calculations for robotics right now). Although samples are still available, the starter kit I got isn't.

Datalink
So, thinking about my upcoming vehicles has me plotting out datalinks. While my Nordic based RF-24G transcievers are good for burst (1Mb/s) low power communications, they're going to drop off after a 100 feet or so, even out in the open. Something new has come to my attention, though. The dev kits for Aerocomm are readily available online at Mouser. 900MHz and 80Kb/s isn't too bad, with decent range. Higher transmission speeds usually demands higher frequencies (due to channel limits imposed by the FCC), more power to get to the same range, and more complex hardware (both electrically and mechanically if it needs a steered antenna). I'd love to get a more complex DSSS system to reduce interference, but that takes more power and more importantly money. We'll see where I go from here.

Another option is finish getting my Ham license and go into the 10GHz range. 900MHz omni for commands, 10GHz transciever for 10Mbit data transfer. Might be fun. I'd rather build a radar around the 10GHz gunnplexer, though. Maybe with an FPGA rear end a dual mode unit would be feasible.

Polar Sight

2005-01-25T13:51:00.000-06:00

I've been thinking about vision systems, and one idea popped into my mind. I know the intelligent weapons of the US army use this trick. Take a masked line CCD and spin it around a linear. By knowing the RPM and at least a single opto-trigger to track the RPM, an accurate polar image can be created. I've been thinking this could be interesting for vehicle guidance. Simply knowing the angle and the CCD that a "bright" target is lighting up, the position of an object could be detected. I might have to try this. Even with a single heat sensor, the ability of this design to easily zero in on a hot source could be interesting.

On a related note, how to do you control a spinning target? Especially if you don't have a stabe "zero reference"? One idea is to mount a microcontroller and a solid state gyro on a motorized plate. Spin the plate to correct for gross spin, and use the gyro for direction control and minor spin stabilization.

RC Core - CANoPIC and related

2005-01-20T08:36:00.000-06:00

Well, I've got a few PIC's on order now. Some giant, some fast, some with USB. So, after I get back to the RC core and get all but the CANoPIC interface hammered out, my next step is to take an 18F2550 (or maybe the 4550, depends on how many I/O I want in the end), attach an SPI EEPROM and an SPI CAN Bus unit, and build a USB-CAN bridge/sniffer for developing and debugging my CANbus designs. Actually, I should probably look into SRAM just so I don't wear an EEPROM out. It's not like I'm searching for power-off persistant memory.

Of course, this means I need or order my ICD2 and hot air rework station soon.

Side note:
I've spent too much time plotting on the Silly scope, I need to get back to realistic projects that I can see real output from. Anyway, to build and debug the silly scope, I need an oscilloscope first. Let alone I don't think I'll be able to have a snowball's chance in hell of building it with double sided, or even a 4 layer board, especially if I throw on the DDR SDRAM DIMM slot. I'll attack it again later with concerns over external memory after I get a few surface mount PCB's designed and built. My ideas have taken it beyond a basic digital storage mixed signal scope to something that could be used for DSP, wireless base stations, radar, who knows. Just too much for someone who's still learning the basics and getting his feet under him.

Silly Scope - Returneth of the integrated card and DSP notes

2005-01-17T11:44:00.000-06:00

So, I've been looking at the timing requirements for DDR SDRAM. Given the nature of the 100+MHz frequency domains, I'm starting to think a tiered structure with connecting pins just isn't going to work. So, back to a single card with DDR SDRAM, an FPGA, and the analog conversion equipment I'm working with. Oh well. I was hoping to avoid having to redesign my board to switch ADC and DAC hardware. The DDR I've considered building onto the card from the beginning simply because of the strict timing requirements.

Now, a longer term idea (for the heck of it) is ordering enough samples from Analog to put together a full wireless transciever interface. Just a thought, they do have parts for the whole datapath.

Now, for my NEXT trick...

Analog has a few good references online, for free, for DSP.

The Scientist & Engineer's Guide to Digital Signal Processing

Mixed Signal and DSP Design Techniques

They might be a bit Analog specific, but they're general enough and deep enough to get people going. The first one's over 650 pages printed, and I haven't looked at the second yet.

Silly Scope - Evolution to DataStack

2005-01-10T11:54:00.000-06:00

This isn't a true evolution per se, but an extension I've been thinking about. I always wanted to loft some good hardware in my rockets, and the stack makes it strong enough and dense enough to do in a small-ish rocket.

A circular format of the boards will let us fit a bit more on them for the same hole spacing. I'm thinking of moving away from the four quadrant design to a two half design. Two digital power rails, two analog power rails, two pin grids. This will result in the need to control what uses what datalines to have more than 2 boards attached. A new addition will be a JTAG rail. This, when combined with a DIP or jumper on each board, will allow a single JTAG cable to program the entire stack. Going with 2 hookups leaves more space and "stack access" on each side for airflow or other situations (like access to a CF card slot).

Now, for the addon boards. Barring low latency parts like a SRAM/SDRAM board, all other boards will have a CPLD onboard. Probably a Coolrunner II. They can interface 1.5V to 3.3V and act like logic shifters, and also implement high speed interfaces (simplifying the databus to a single voltage requirement). I still plan to hook up only half the bus to the CPLD to keep two independent busses. A CPLD on each board will simplify reconfiguration for different stack designs. This does raise the cost a bit, though. The flexibility and I/O standardization is worth it, though. It also lets those do PCI or similar bus standards for those who want a true databus as opposed to my partitioned databus. Only other problem is that to get enough pins, the CPLD may have the same packaging as the FPGA!

Silly Scope - Research Break and future ideas

2005-01-09T16:53:00.000-06:00

I've spent too much time on this already, especially since it's still out there in "pipe dream" territory.

Anyway, for future reference, I've decided to go with the Xilinx Spartan 3-400. Big enough for most applications, it's also the largest QFP format chip, so a user doesn't need either an IR oven or a hot air rework station (I want to buy/build both), so others can work this design.

It's fully supported, development hardware is available for low cost (Digilent-400 version of the starter board), and hopefully the free simulator will run it.

And hopefully I can run it off of batteries. One current idea is to build a tiered design (similar to PC/104). Fixed size (square, circuilar is considered for sealed tube applications). Radially symmetrical, it'll have 4 digital voltage busses (GND, 1.8V, 2.5V, 3.3V, 5V), 4 analog ground busses (AGND, 5V Regulated, Unregulated). There will also be each bank brought out to a databus. Only those components that need access to all the databusses (like the FPGA) will be connected to all of them. All other boards will have passthroughs for the signals, and be connected to only one databus. If multiple FPGA's need to be mounted, a spacer board that passes only one bus through (and all power lines) will be required. Turning any board will just put the sensor on a different bus without any major bus arbitration (important for high speed apps like 200MSPS ADC's). This means that for "generic" boards, the most that can be used are 4, one per bus block. Custom boards may be able to use a CPLD and a jumper to split the busses into inside and outside, or left and right, etc. to at least double the possible board count.

As soon as I remember my FTP passwords, I'll upload a GIF to illustrate, and a possible board "stack" idea (Digital camera control and DSP or a radar stack).

Anyway, this is going on hold. I'd love to spend the $100-$200 and get everything I want, but my R/C core is waiting.

(Edit!)

Basic board layout

Generic ADC sensor stack

Silly Scope - Digilent to the rescue!

2005-01-08T04:23:00.000-06:00

So, I wander around thinking of how best to start prototyping my FPGA based silly scope. As much as I'd like to start designing my FPGA based super O-scope card PCB, I know I should build a breadboarded design. Well, a while ago when the Spartan3 was first released, I looked at the official Xilinx Spartan3 starter kit. From there I wandered to Digilent, the maker of the board and lots of add on boards for the hobbyist/student. My only disappointment was that it came with a 200K gate chip.

Well, I did a search. They now offer the same board with a 400K chip for $119 vs $99. Perfect.

Add in all their expansion boards (Wire wrap boards all the way up to 1MSPS D/A and A/D board), and you can probably get away with anything. I'm interested in the AD/DA board and their DIO5 computer addon board.

For a more compact version of that, and cheaper, Nuhorizons has their Spartan3 Development Board. A little cheaper, too.

Now, for the more extensive design work, I've looked at two different boards. One is made by AVnet. It's got a 1.5M gate FPGA on a PCI card. Nice, and it allows for a user to design direct access to the PCI bus in, bypassing any other work and allowing data to be dumped into main memory directly, greatly increasing capture bandwidth.

Another option is another Nuhorizons board, $450 for a 2M gate board designed for very high speed DSP. Fast, huge amount of space in the FPGA fabric, has ready made cards for A/D (135MSPS at 14 bit works for me, still looking for the price). I'd love to get one. I'll hold on, though, we'll see what my FPGA musings bring first. I sure don't plan to spend any money on software anytime soon for this hobby. It's got dual Ethernet, CAN, low speed A/D and D/A (audio speed), LCD panel support. Hmmm... it's just about perfect for a central processor for my large exoskeleton/robotics project. Must contemplate...

Silly Scope - Programmable Logic

2005-01-04T14:29:00.000-06:00

Been researching a few of the FPGA's out there. Actel, Lattice, Altera, Xilinx. Mostly Xilinx. I know people who swear by Altera, but Xilinx has be most flexible free tools, and supports their entire low cost Spartan3 (to 4million gates and embedded multipliers!) line in their free software. Yeah, I'm not going above a surface mount design (400k gate model), but it's nice to know.

Yes, I am reading through the entire 192 page reference doc on the FPGA, and learning a lot.

R/C Core - Transcievers

2005-01-03T15:32:00.000-06:00

I'm no RF guru. On the contrary, I'm a baby. Hence, I need a little... "help". I'm using a transciever based on the Nordic 2.4GHz chipset...

2.4GHz
http://www.nvlsi.no/index.cfm?obj=product&act=display&pro=64 ($5.40)
433/868/915MHz version
http://www.nvlsi.no/index.cfm?obj=product&act=display&pro=83 ($7.00)

These are available at http://www.sparkfun.com/ (along with lots of other very useful items). I bought some 3rd party 2.4GHz transciever boards from them for $20, which is plenty to get me going. I plan to eventually use both of these in my designs, and throw on power boosters for greater range with my own PCB's.

Until that time, I'm doing good as it stands. I considered Zigbee, such as those chips available from Chipcon, but they're a bit expensive at $9/chip and need external parts. However, they are true Zigbee parts and have integrated 128 bit encryption, which is intiguing. Still, I'll hold off on that. I'm not trying for a secure network, and I doubt I'll be hacked running my R/C car around since it's not 802.11b (great speed, range, oh dear look at that power drain...)

Silly Scope - Add On Board Layout prelim thoughts

2005-01-03T11:31:00.000-06:00

So, my oscilloscope design's going to have a data/power backplane, one power supply board and I/O board (maybe the same board), and multiple data capture boards. I'm plannng on a VM state machine that's hopefully compatible with Bitscope (or at least ASCII streaming so I can capture the data to Matlab).

Mid level cards will be built similar to the Bitscope. A PIC for communication with the databus (and identifying itself, housekeeping, etc), a CPLD doing the ADC interfacing and data dumping to the capture SRAM. Also logic analyzer (again, Bitscope compatible PODs perhaps). I MAY base the databus on standard 3.3V PCI, which many CPLDs can be used as the data bus conversion, or maybe ISA (ditto).

High level cards will be a beefier version. PIC or maybe dsPIC for the housekeeping, CPLD for bus buffering, Xilinx Spartan3 (or maybe the Cyclone II from Altera) for a strong but inexpensive system. It's gotta be able to keep up with 100-200MSPS at 8-14 bit from 1 or 2 ADC's (not certain yet). I'm avoiding large ball grid/pin grids as you really need multilayer for that, limiting me to the PQFP-208's package, so the largest Spartan3 I can use is the 400,000 gate version. That gives us over 256k of buffer RAM onboard, which is as deep as the Midline Bitscope-310.

Now, the Spartan can do DDR RAM speeds, and a max speed of 326MHz, which should be fast enough to get the data out. There are DDR controllers out there. However, DDR DIMM's are 168 pins, which would devour ALL my I/O (141?). So, custom memory boards and individual chips are required. Easy enough, Hot air rework station and cheap DDR-333 DIMMs give me the RAM I need.

So, what's the backplane providing? I'm thinking:

16-32 bit bidirectional data path.
Card Select
Digital Ground
Analog Ground
Digital Power (5V)
Analog Power (24V?)
Capture Trigger Start (single signal)
Capture Sync Line (continuous capture sync)

The card's will have to attenuate their power supplies down via linear regulators to what's required for the boards themselves. Although this wastes power, it'll provide a cleaner connection, reducing interference from adjacent lines. The analog power is designed to be attenuated down, as it is very susceptible to digital noise.

Now, back to looking through the Spartan3 spec PDF...

Digital Silly Scope - Analog research

2005-01-03T01:52:00.000-06:00

Well, I've been looking at Analog to Digital Converters for my Oscilloscope project (freshest on my mind). Ran across 3 candidates:

TI ADS5500, 125 MSPS 14 bit ADC

National Semiconductor ADC 08200, 200MSPS 8 bit ADC

Analog Devices AD9430, 170MSPS 12 Bit ADC

All three are great, having examples on how to hook up the parts with high bandwidth op amps (their own of course) for stable operation and signal conditioning. Now, since I plan on having multiple boards for the Silly Scope, both are viable for their unique benefits. I'll probably start with the National ADC because it's a simpler package and more extensive notes (barring schematics for demo boards from Analog). However, I don't want the expense of a 4 plane board (when I get there), so maybe I can bend the rules for a 2 plane design? We'll see.

Speaking of analog, I realize more and more I need to hit my analog design books and hammer out more understanding of R/F and analog in general. Digital design frankly is easy (except FPGA optimization), everything always hangs on the real world analog design.

Since this is a VERY low cost operation for me, I can obviously get free samples of all of the above :) Some of the devices are very expensive(Analog, $88), some are fairly cheap (TI, $4), so production would affect these, but I'm looking for speed and resolution for my oscilloscope.

I know I really should buy an oscilloscope before trying to build one...

Anyone have good sources (web and textbook) on RF(airwaves and high speed PCB) design? (Yes, I expect to be told 4+ layers are REQUIRED).

Too many ideas, too little time...

2005-01-01T15:33:00.000-06:00

So, I've started a little corner of the internet for posting my ideas. I'm not going to rant and rave about life, the world, or otherwise, but interesting projects I've run across online, useful websites, and ideas bouncing around my head. So, why Technical Alchemy?

(no, this is not LEGO related)

I went to college to be a mechanical engineer. I don't do that right now at work (still want to). However, I have an interest in learning, so I'm dabbling in ideas ranging through electronics and computer science. It's an easier pasttime than trying to get a machine shop into my apartment. However, I have only basic electricl/electronic knowledge, and a little programming skill, so it might as well be alchemy at this point. Situations like that tend to change very fast for me, though.

That machine shop will come when I get a house, then I'll start tackling plastics and composites.

So, for the moment, here's the current list of hopeful projects and some notes on them.

2.4GHz R/C basic control system (BCS) - Currently on my breadboard as I'm slowly working on the PIC code to implement this. The 2.4GHz transcievers are currently prepackaged, so no RF design headaches.
Intertial Measurement Unit (IMU) - Haven't bought a GPS yet, it'll be part of an upgrade to the R/C BCS. Also haven't started on the codework.
CANoPIC - CAN over PIC. Bascially a series of modules (which the R/C BCS will be one) that allow me to implement CAN based networking of a given common R/C function, such as a dedicated brushless motor controller. This is for my own ease of work and an experiment to reduce the interference common with R/C designs. More on the modules later.
UGV - The UGV will be built as a custom vehicle body with a modular arm for poking cameras into crevases. It'll be the testbed for the R/C BCS. I could buy an R/C car for this, but where's the fun in that? Although that might happen later when the system needs to be more rugged.
UAV - There's a whole bunch of ideas floating around here. Although all of them depend on the IMU for guidance and to tell the airplane where to circle, the plane itself is up for grabs. Standard fixed wing powered-glider, rocket boosted glider, and scissor wing rocket booster (I like this design on principle) are all possibilities, in increasing order of difficulty.
VTOL - Electric or gas powered VTOL. Maybe similar in design to an Osprey, but I know to get ANY performance out of it, I'd need to keep the weight down, so no UAV stuff. I'd still need the IMU onboard as I'd like to make it computer controlled and docile (the IMU could react faster than I could). However, I'd definitely need access to a machine shop for this one. No one makes the variable pitch blade hubs I'd need and the chopper ones don't have enough pitch.
Pan-Tilt-Zoom Camera - There's probably going to be 2 phases to this. First one will use a micro NTSC camera I have laying about. Second version would use a Panasonic Lumix DMC-FZ3 (3Mpixel, 12x optical, optically stabilized, about a pound for weight) that would be hacked apart and the controls attached to a microcontroller. In either case, the NTSC video out would be hooked into a frame grabber and hopefully something similar to the CMUCam (automated tracking of a target especially) could be worked out. The FZ3 would give the design a zoom lens, image stabilization, and a 3Mpixel photo capacity. I'd also like to hotwire the photo capacity to allow me to transmit the pictures back across the datalink without needing to land, but first things first.
The Silly Scope - a modular oscilloscope. It'd have a power and computer access board plugged into a backplane. The remaining backplane slots could be logic analyzers, high speed ADCs, and the like. Power and databus back to the master (USB probably) controller would be provided along the backplane, as would be a sync/trigger line for simultaneous capture operations. I'd like to make it Bitscope compatible and open hardware.
Phased Array Radar - I'd love to make a small radar for the UAV. Now, this is far beyond my ken right now (RF is still black magic to me). However, the Silly scope modules would be a good first start. One of the possibilities is a module running a PIC for control, having an Xilinx Spartan3 for onboard DSP and datacapture, and dual 200MS/s AD converters. Oh, and some very fast memory. My primary use is for ranging, although I'd love to be able to do synthetic apeture tricks with it. I'll probably start with a sonar system as it requires far less speed and cost, but doesn't have the effective range for use as a radar altimeter, for instance.
Walking Robot - Very similar to the Robo-ONE designs, and therefore very expensive (30 R/C servos x $80 for high power digital ones? I think not). Maybe later, though.
Exoskeleton - Definitely on hold till I have a garage. I'm not aiming for much strength. I was actually thinking of building a costume around it (therefore light weight) and just worrying about that weight. The control "suit" and the frame itself are to be separate, both for ease of application (may not be comfy, though) and so that the frame can be tested without risking life and limb of the tester. Seven feet of tubular bars, heavy batteries, pneumatics, and car window motors (cost!) is just too much for an apartment. The motion capture suit, however, can be built. Could be fed into a computer for animation purposes (for my brother).
Digital Dustbunnies - Similar to Smart Dust, just my own needs, right now, not in the future. Small PICs with a few sensors and a 2.4GHz transciever get scattered about randomly from a UAV air drop of an air cannon "shot load". Heat/sound/motion/sesmic sensors allow for rapid scanning for anything alive in the area. Although good for Search and Rescue purposes, I'm far too cheap to allow them to just be thrown away right now, even for a good purpose. I'd have to go and pick them up.
Aircannon - One of my original ideas from a long time ago. It'd be more like an air mortar. Short, wide barrel, high angle. It would have used smart ammo that would have communicated with the launcher via a 125KHz carrier (RFID tech) to specify what type of round it is. The ammo would be loaded either in a belt fed system or a revolver type magazine and would have been breech loaded. Very much fully automated. Primary loads would have been the Digital Dustbunnies, paintball cluster rounds, Brilliant Paintball Rounds (think parachute deployed self targetting single shot paintball round), the original UAV idea (Fast to high altitude, parafoil wing deployment), and a few more I can't remember right now. This one requires a farm away from the city to actually not be arrested, and who knows if even that is safe these days. Oh, hi Mr. Homeland Security Officer...

Ok, that's it for now, off I go. Wonder if I missed any?