Servo Controlled Potentiometer using Rotary Position Sensor

I need digitally controlled potentiometers but I want real pots and not a digital potentiometer chip because I want to integrate this with conventional relatively high voltage circuits like those you might find in a guitar amp.

My current idea is to mate a Rotary Position Sensor with a Servo:

The Murata SV01 Rotary Postion Sensor costs $0.95 USD and it's basically just a potentiometer with a D shaped hole instead of a shaft: A cheap micro servo costs$3.50 USD:

I don't want a motorized pot because they're huge and expensive by comparison and I don't need a shaft. And the servo is easily controlled using a PWM output of a microcontroller.

So the question is, is this feasible? I'm not an engineer but I'm just concerned with coupling the two devices, accuracy, control, robustness, etc.

If you think it is feasible, can you recommend where I might obtain the necessary hardware to mate the knurled plastic shaft of the servo with the 4mm D shaped hole. I was thinking a mini-PCB could serve as a base with screw holes for the servo mounts and something to solder the Rotary Postion Sensor to.

• You assume in this question that a pot is necessary, but you don't sound qualified to make that decision. A device "like a guitar amp" does not operate on what would be called "high voltage" in most contexts, and unless this is a very odd guitar amp, handling those voltages with solid-state electronics may be a cheaper, simpler, more robust solution than an electromechanical solution as you suppose. Some information about the actual problem you are trying to solve will probably result in better answers. – Phil Frost Mar 9 '13 at 3:22
• Have you considered that servos are usually only 180 degrees (or less) and that potentiometers are like 270 degrees? – JRE Jun 1 at 8:25

Yes, that should work fine. The rotary position sensor you have pictured is made for servos like this; if you open the servo you will find such a pot used for position feedback.

One concern is crosstalk. The PWM signal is in the audio range, so any signal that bleeds through will be audible. This can be engineered around. I suggest separate power supplies for the position controls and the audio. In particular, do not allow the ground signal to be shared between the position and audio circuits.

The only problem I foresee is the servo not being able to turn the pot. If the servo is weak (and those tiny ones are quite weak) and if the pot is stiff (some of those little pots can be) then the servo may not be capable of fine control. It may be unable to quite reach its target position, or worse, it may not move at all. As usual, the only way to know is to try it. Get the pot first, and if it seems to rotate fairly freely, then you'll probably be fine.

Like $5 AD5290 digital potentiometer rated to 30V or$2 MCP45HV51 rated to 36V.