I am trying to find a way in order to turn an car amp's bass level knob left and right using an Arduino's digital PWM pin. I am thinking that a stepper motor would be the correct motor to use in order to do this or no?

Also, would there be a better fitting motor to do what I am looking to do without much needed modifications to the bass level knob in order to attach it to the motor to turn it?

The bass knob looks like this:

Bass level knob

Any insight would be great!


closed as off-topic by JYelton, Chetan Bhargava, Joe Hass, Daniel Grillo, Matt Young Feb 26 '14 at 13:12

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    \$\begingroup\$ Migration candidate for arduino.stackexchange.com \$\endgroup\$ – JYelton Feb 26 '14 at 4:08
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    \$\begingroup\$ You keep rolling back my edits, which were done to fix some basic readability and capitalization issues. If you feel such edits were incorrect, please explain why. \$\endgroup\$ – JYelton Feb 26 '14 at 17:26

You could consider using an RC servo. You will want one that will rotate an appropriate number of degrees (maybe 240 or 270). Most only rotate 90 or 120 degrees. One possibility is a Henge MD260, but shop around.

The interface is simple- a 1msec pulse every 20msec causes it to rotate to one extreme, and a 2msec pulse every 20msec causes to rotate to the other extreme, 1.5msec puts it in the center (sometimes these times vary a bit from servo to servo).

You don't have to 'home' it as a stepper (and gearbox, most likely) would require. An RC servo has a built-in feedback potentiometer connected mechanically to the output shaft, so you control absolute position rather than incrementally moving it from wherever it happened to be last (perhaps after the power was interrupted).

If you can live with 180° rotation, there are more choices, and you can get ones with a standard spline which fits shaft couplers to a 1/4" (6.35mm) shaft.


A limited-motion servo does exactly this. Its angle is controlled by the duty cycle of the PWM pulse train. You can probably connect it directly to the potentiometer shaft with a shaft coupler after removing the knob.

Make sure you test carefully what minimum and maximum values you can safely use so that you don't damage either device from twisting stress during operation.

  • \$\begingroup\$ And I'm pretty sure there's even a servo control library... \$\endgroup\$ – Matt Young Feb 26 '14 at 2:12
  • \$\begingroup\$ Indeed. \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 26 '14 at 2:12

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