I have a problem. I am following this guide about controlling a NEMA 17 stepper motor: https://www.makerguides.com/a4988-stepper-motor-driver-arduino-tutorial/

I uploaded the code to my arduino uno and powered on everything, but the stepper motor doesn't rotate, except when I put my finger on the metal screw of the a4988 driver. The arduino is powered by a 5v 1A adapter and the a4988 driver is powered with a 12v 2amp adapter.

What is causing this?

  • 3
    have you connected all the grounds?
    – chrisl
    Commented Nov 15, 2020 at 14:24

1 Answer 1


The "metal screw" is a "trim potentiometer" that is used to set the current used to drive the motor. It sounds like you may be altering the current when you push against it. Try turning it to different angles to see what effect that has on the motor.

Alternatively if it only ever works when you push on it then it could be that you have a faulty potentiometer on your board.

  • Despite not being able to take it out of the circuit, it is probably safe for you to put a meter across the pot while the board is unpowered. Certainly worth a try if you get the point of feeling that you need to throw one out. You can fiddle with it and see if you can notice what Majenko mentions, understanding the results may be skewed by being in circuit. Admittedly, it may be game of twister to get your probes in the right place and manipulate the trimpot the way you want.
    – timemage
    Commented Nov 15, 2020 at 15:10
  • 1
    Could also be a cracked solder joint connecting the pot to the board. If that's what it is, it could be fixed by heating up the bad solder joint(s) and applying more rosin-core electronics solder to them.
    – Duncan C
    Commented Nov 15, 2020 at 23:39
  • The stepper driver is broken. Bought a new one and everything is working now! But I had to trim the potentiometer indeed! Commented Nov 16, 2020 at 0:10

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