Electronic – What’s the automatic equivalent of a variable resistor


I have a circuit which controls the volume on a speaker by a wheel which is attached to a variable resistor – I want to reproduce this but instead of using a manually operated variable resistor, I want to use …something else instead – Ideally something where you can apply a voltage to change the resistance from low to high.

I've done a little research but I think I'm being stumped by not knowing what I'm actually looking for.

Best Answer

You can use a transistor to do this. Although less common that the other types, a JFET works much like a voltage controlled variable resistance. You'd have to apply an analog voltage to the gate to get a specific resistance. You'd have to be careful about the range of this voltage. The Drain and Source would act as the effective two terminal resistor. Even a mosfet has a linear resistive region so this is not your only option. There are many other options as well which I'm sure will be mentioned.