Noise / ground problems with motorized potentiometer

I am trying to drive a motorized potentiometer from an Arduino Nano. The Arduino reads the pot’s resistance using analogRead() and then drives the motor using a TB6612FNG motor driver until the measured resistance matches the desired value (within a certain epsilon of course). A 10V DC converter powers the motor driver and is also connected to the Arduino Vin.

When connected to my PC via USB cable everything works flawlessly with me moving the pot to the desired values. As soon as I unplug the USB cable the circuit becomes highly unreliable, with analog values fluctuating a lot and correspondingly the motor jittering around the set position. I was trying to get a better idea of what the induced noise looks like, but of course as soon as I connect my oscilloscope’s ground lead to the circuit ground the problem goes away.

Things I have tried:

  • increase distance between motor and sensor leads
  • adding 220uF electrolytic caps between Vin/Gnd and 5V/Gnd
  • adding 0.1uF ceramic caps between the above points as well as the motor leads

None of these things have made a difference. What are some other recommendations?

Motor specs here (10V DC, max. 0.8A, 10kOhm max resistance):

TB-6612 breakout board:

Please don't use the breadboard view of F**ing. There's a perfectly good schematic view available, which is so much easier to read. It's just not as colourful.

What are the specs on the "10V DC converter"?

If connecting a ground solves the problem, I would look for a missing ground connection you forgot somewhere.

Not using Fritzing, but if it helps, here is a schematic.

I don’t understand what you mean- if a ground connection was missing how would I be getting power at all?

On some breadboards the power rails are not continuous. Those usually have a break in the middle.

Your first picture does not show a ground connection from motor board to power supply, are you sure the second pic is correct, which ground point do you connect scope probe to?

Do you have the breakout board or the IC itself?
On the breakout board do you have Vcc connected to the 5V of the nano.

Have you got a DMM?

Monitor the voltage of your supply.
Monitor the 5V on the Nano.
While the project is malfunctioning.

Please draw a diagram by hand from your project, this reverse engineering may find your problem, photograph it and post it to us please.
Note down pin names and part values.

Thanks Tom… :slight_smile: