I'm trying to control a universal motor run from a 240V power supply using a micro-controller. There is a existing PCB that uses a potentiometer to vary the speed that I am trying to replace. I've identified the triac but the rest of the parts are covered, I've assumed it is something like this:
I've been looking into IC solutions, BJTs, MOSFETs, etc to replace the potentiometer but am struggling to find a solution that I can fully understand and that will simulate. The micro controller will be an Arduino. The motor power is up to around 750 W.
Any help pointing me in the right direction would be much appreciated as I've spent so much time reading around the subject but am not confident with any of the solutions.
Best Answer
This is not a particularly easy circuit to control through a safe galvanically-isolated connection. Normally the approach used in a production design would be to couple the microcontroller to the mains via an optocoupled zero-crossing detector and then trigger the triac through an opto-triac. The power would be a function of the delay between the zero crossing and the triac trigger.
If you really want to use that "light dimmer" circuit, it's possible with a light-dependent resistor (LDR) and a variable light source. LDRs may be hard to buy in some countries because they contain cadmium which is not RoHS compliant.
By the way, I'm not sure what you intend by that voltage source but it has a rather uncommon RMS voltage of 170V. If you intend to have 240VAC RMS @ 50Hz, you should use about 340V for the peak voltage (240\$\times\sqrt 2\$).