I'm designing a round knob positioned by a stepper. The knob is intended move by an external force while positioned by the stepper. I'd like the stepper to release (power off) when the knob is manually turned.

Is there a way to sense the application of external force via the stepper drivers ie a current sense ?

I know there is a current spike when the stepper position stalls. I'm unsure whether the current spikes when already positioned and the position manually moved.

  • 2
    $\begingroup$ use a position sensor $\endgroup$
    – jsotola
    Jan 10, 2019 at 3:20
  • $\begingroup$ I'd like to keep the cost down and parts to a minimum. $\endgroup$
    – garyM
    Jan 10, 2019 at 7:34
  • $\begingroup$ a position sensor may actually be the only way to detect external influence while the motor is being positioned ..... you don't really have any other way to detect if the motor skips a step ..... it may be possible to use a scrap optical mouse sensor to detect the movement $\endgroup$
    – jsotola
    Jan 10, 2019 at 21:04
  • $\begingroup$ I've been looking at haptic technologies. In '88, companies like Neve introduced motorized faders (linear potentiometers). They used a dual resistors, one for signals and the other for position. I hope we can do better..Thanks for the suggestion using Optical mouse sensor.. its a good idea. If I'm going to use a but leaning towards a torque sensor, a bridge strain gauge on the shaft, although I don't like the leads. . Others may be touch sensor or press down switch on the knob. $\endgroup$
    – garyM
    Jan 15, 2019 at 7:32

1 Answer 1


I am not sure how you are driving your stepper motor. In case you developed your own way, you could connect an analog pin to the wires that drive the stepper motor. These should be able to detect an induced voltage if the stepper is turned without being driven.

  • $\begingroup$ I haven't selected the drivers yet. I think I'll be using a STI's L6400 series part. I was really hoping to find someone who's solved this problem in the past, I didn't want this to turn into a science project. Detecting tiny induced voltages on a driven stepper is a non-trivial task. The more I'm searching, the more it's looking like a "green field". $\endgroup$
    – garyM
    Jan 10, 2019 at 19:32
  • $\begingroup$ the OP stated that the outside influence should be detectable while the motor is being driven $\endgroup$
    – jsotola
    Jan 10, 2019 at 21:05
  • $\begingroup$ I'm attempting to figure this out. I'm rethinking the modalities, more specifically modulating torque to make the dial easier to turn and detect induced voltages. Microstep drivers/motors inconsistently induce voltages based on micropositions and big step rotation due to stepper manufacturing variation. I'm not doing any machine learning for a movement detector ... Now I know why no one has done this yet $\endgroup$
    – garyM
    Jan 15, 2019 at 7:34

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