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.
Sunday, January 21, 2007
Monday, December 11, 2006
Because Mike Said So
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Fun: Gunnplexer Radar Components
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.
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.
Tuesday, December 05, 2006
Fun Thoughts: Bad Drivers
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.
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.
Wednesday, November 08, 2006
Sensors: Ultrasonic Phased Array
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?
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?
Wednesday, November 01, 2006
Oops! The Laser Rangefinder
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).
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).
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