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Motor noise and ADC measurements

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trix312

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hello

I'm trying to get a few photo transistors to control two DC motors. I'm using ADC. Without the motors running I'm able to obtain decent values for ADC, however when the motors are running the ADC reads all kinds of nonsense and the motors go crazy. What is the best way to reduce this interference, I have tried averaging the measurements in software, adding diodes to reduce back emf and reducing the speed of the motors which has helped but not enough. What is the best way to solve this issue without adding too much extra hardware?

Thanks.
 

Your problem is typical whenever sensitive sensors are located close to high-power lines.
I would start with "cleaning" motor power lines. You can use R-C filter(s); use an oscilloscope to adjust the values to minimize line noise.
Second step usually is to separate signal and power lines. Use a well filtered DC line for photo transistor circuits, and use TTL inverters or opamp(s) to transform the high-impedance sensor output(s) to low-impedance TTL lines that are less sensitive to noise. Consider locating the sensors in a grounded metal case for screening. Connect motor bodies to ground and use screened cables and good connectors.
 

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