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I a using a MOT-B24400 motor which has a built in controller and only needs an external 5k pot to control the speed, plus power of course. I have this wired to a relay with a button to send a signal and engage the motor. Everything works when I use an analog pot. I was wanting to change it to a digital pot (MCP-4151) in order to "ramp" the speed up and down depending on a count coming into the pi. Without the motor attached, the digital pot changes values as expected. I have triple checked all the connections and believe that it is all right. I checked the motor pot connections and got 5vdc across the high and low with only power connected. Is there any reason this would work with an analog pot but not a digital pot?

connections (MCP4151-Pi/motor): 1-CE0, 2-SCLK, 3-MOSI, 4-GND from GPIO, 5-"high" on motor pot connection, 6-"wiper" on motor pot connection, 7-"low" on motor pot connection, 8-5vdc from GPIO

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A digital POT is similar to a digital DAC. You can change the output voltage by setting the input value.

As long as your motor controller just needs to sense voltage it should be fine. The digital POT will not supply much current at that voltage though, perhaps just a few milliamps.

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