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Re: Ultrasonic Interference
Tony,
there are two possibilities here. One is electrical noise and the other is acoustic noise. Since the sensor is only putting out 40kHz it is possible that the motors generate enough acoustical energy in the desired band to swamp the sensor input or to modulate the body of the sensor. You can try to wrap the sensor in some foam, fiberglass or a chunk of pool noodle and see if that effects the interference. If it does then the motors are making significant noise on frequency. The other possibility and the more likely one, is that the sensor amplifier is not shielded and so therefore receives all of the generated electrical noise and boosts it along with the received acoustic signal. Without a scope and some controlled tests it is hard to tell exactly what is the problem. Considering that the output is a 5 volt digital signal, it is unlikely that the cable is picking up enough noise to be a problem. You can try shielding the sensor in a steel box but will need to tie the shield to something to drain away the charge. Robot frame or battery common might work but not both please. 3M sells a nice product that is a copper foil with a conductive adhesive available from Digikey. It is expensive and it comes in various widths. An 18 yard by 1" wide roll is about $50. You can solder to it with care but it may not take care of all of the interference.
You didn't mention it, but are you using Jags in this application? It is possible that the third harmonic of the switching frequency is close enough to produce significant in band noise.
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.
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