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Unread 18-04-2011, 11:40
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Re: Ultrasonic Interference

This is most likely just a big noisy motor causing electrical interference on your bot. There's a few quick and easy things you can try to filter the noise down to an acceptable level. It'd be great if you had an oscilloscope to measure things and see just where the noise is coming from, but if you did, you wouldn't be posting here, so...

First, put a 1 microfarad (uF), non-polarized capacitor across the leads of the 775, as close to the motor as possible. This should make the biggest difference.

Second, connect a pulldown resistor from the signal line of your ultrasonic to GND. This should probably be in the 1k ohm range. I don't have specs on the Vex ultrasonic handy, so I can't say what it will tolerate here, but 1k seems safe. You'll know if it's too large because you won't get anything back from the ultrasonic even with the motor off.
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