Speed Controller questions

Is there any way to modify one of these so I can control it with an Arduino? It is controlling a fan motor speed and working well, but I'd like to be able to control the speed remotely.

I know I could add a servo to turn the knob but am wondering if there is some way to do it directly with Digital or Analog pins. I am OK with soldering parts.


An AC motor speed controller works like a [u]light dimmer[/u] (with some special consideration for the inductive motor load). You have to "sync" to the AC line frequency.

You could use the TRAIC from that circuit, an that's about it. You also need optical isolators between the Arduino and TRIAC and between the AC and the Arduino's phase-detection circuit. (Or you can use a transformer to isolate the phase-detection side).


A servo attached to the potentiometer knob may be the easiest and safest method.

You could replace the potentiometer with a few resistors in parallel and have a relay on each resistor. By controlling the relays you can adjust the resistance in steps. It won't be as smooth and continuous as the pot, but it should work. Do you know how to calculate parallel resistance?

Note that the resistors are going to see AC line voltage so you want the arduino and anything that you can touch isolated from the relays.