I need to emulate a component that measures an input mechanically and varies resistance from 0 to infinity (a more detailed set of specs list it at 20-1,000ohms, though I'll have to actually check its true values myself once I have physical access to it).

My aim is to replace this troublesome mechanical component with a current (read as available and serviceable) component, and convert the signal from the new component into an emulated signal (varying resistance) from the old component.

I am not certain as to the resolution required (how big the steps can be), though it may be able to handle 50ohm 'leaps', just judging by the range of mechanical movement and my past experience with replacing similar mechanical systems with ready-made kits for conversions. I'd like to smooth the curve a whole lot more than 50ohm leaps though.

I have barely an idea where to begin on this. I thought maybe a resistor ladder and a set of transistors triggered by the arduino to connect into the different points in the line, though I suspect there has to be a better way to achieve a much better result (and I don't think I have enough outputs for that anyway).

Is there a digital component that can vary its resistance using a PWM signal or maybe an analog signal from an arduino?

FYI, I greatly appreciate your input.


The controller provides a constant voltage to the component, and the controller then looks at the ground (the voltage over a static resistor) I presume. It is an actual load.

I may be able to provide a variable voltage to the controller on its ground pin, though I have never seen that done on them before. I think that may be the trick, though the controller may(??) dislike it? I can try that.. The next best thing (only 2nd because it requires more components) would be the digital pot.

Anyone ever forged a return signal on a circuit thats supposed to supply its own constant voltage to a resistor type sensor?

  • The idea of using a servo to move a potentiometer came up, and that doesn't work because it cannot keep up (its too slow).
    – Eric
    Oct 11, 2014 at 6:34
  • 1
    How is the resistance being used? is it an actual load?
    – BrettAM
    Oct 11, 2014 at 6:50
  • Does your system really need a variable resistor, or is the variable resistor only used to generate a variable voltage. If the latter, you could just use a digital DAC.
    – Gerben
    Oct 11, 2014 at 12:02

2 Answers 2


What about a digital potentiometer Digital Pot

Many types available, generally controlled via a serial interface e.g SPI


A JFET can act as a voltage-controlled resistor. It will need additional components if you require precision (a shunt resistor and a couple of op amps come to mind), but it should do. JFETs are rarer than they used to be, but still should be available for a few decades.

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