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Originally Posted by Gdeaver
Digi-key sells Honeywell line of magneto-resistive chips. The Honeywell solution would require some work. They need
op-amps to condition the output for a micro controller. This limits their use
to teams that can make a custom board. Then they need allot of programming to get to a degree heading result. The other solution is PNI corps line of integrated digital compass chips. The 2-axis chips output a binary or decimal heading in a 2 byte spi interface. The PNI solution is much more usable. None of the listed electronics suppliers stock the PNI line. I believe they are available from Newark as a special order. Does this source meet First rules?
Gary Deaver
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The yaw rate sensor, with careful attention to the details posted earlier, will suffice for going straight and measuring heading adjustments during a period of a handful of seconds. Our measured drift rates were quite low.
I spotted the Honeywell HMC1051Z and associated parts on the Digikey web site, and these parts could easily be used to detect magnetic north, or south, by detecting the maximum or minimum of the signal. Indeed, you would have to put some op amps on the board with the chip to condition the signal to something the RC could read, and most op amps will want need + and - power supplies which will add further to the electrical complexity, but it could most certainly be done.
I would not go so far as building a fully calibrated compass, in that there would be a lot of further issues to worry with here, but if the robot needed to establish its absolute orientation it could align itself with the maximum/minimum flux signal from the sensor, thereby picking off magnetic north/south, and then integrate the gyro to turn to a specific heading. If one wants to be able to sort out the heading without turning the robot, you could mount the sensor board in a manner that could be turned by one of the kit servos. A rube goldberg affair, but it it would work and it would not care much if the robot was on a tilted footing. As you infer, you would want the sensor to be relatively clear of any iron, for instance a CIM motor.
With regard to the PNI unit, if Newark is listed as an allowed supplier for custom electronics for 2005 and the part is available from them, I do not remember any rules forbidding "special order" vs "in stock." Only that the part must be available to all FIRST teams from the allowed supplier, at a price meeting the limitations in the rules. We, of course, learn the applicable rules in January...