I have an AC PWM dimmer board from eBay that uses a potentiometer to control the dimming level. I want to replace it with a digital potentiometer that would serve the same function. However, it needs to be able to handle at least 120VAC and 0.5mA. It also has to be able to be controlled by 5VDC from an Arduino, Raspberry Pi, etc. Does anyone know of any such part?

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    \$\begingroup\$ Be very, very aware that... did I say very?: Very! ... this isn't actually an AC PWM modulator, but just a plain old AC-phase dimmer. I see two capacitors, a fixed resistor, a diac and a cooled triac as well as a trimmer and nothing more. Nothing to make a chopped PWM signal. Still not expensive, but just, be aware. Also check that the 0.5mA is in all positions during all points of the sine wave. Could very well be, depending on the fixed resistor value. Too low contrast to make out for me, even on my spiffy high contrast designer monitor. \$\endgroup\$
    – Asmyldof
    May 28, 2015 at 2:53
  • \$\begingroup\$ A digital pot won't work. The voltages involved are too high, and the pot itself is not grounded. \$\endgroup\$ May 28, 2015 at 2:57

1 Answer 1


There are at least a couple of different options but neither is going to be very good.

1) Use a LED / CdS cell combination. The amount of LED current will change the CdS cell resistance - typically from a few hundred Ohms all the way up to several Megohms.

The downsides are: a) Poor Linearity; b) downright awful device-to-device matching.

2) Convert the dimmer design to a standard phase-control circuit using an appropriate opto-coupler (MOC3011). The downside is that you need to sample the incoming AC zero-cross points and have your controller delay the signal into the opto by the correct amount for the particular dimming level desired.

Or: you could simply build or purchase a dimmer designed for remote control. There are many existing designs available, ranging from analog control (0-10 Vdc) or a digital bit-stream or digital PWM control.

  • \$\begingroup\$ It took me a while to get it working but I got the photoresistor and LED combo to work. The downside is the non linearity which you mentioned. \$\endgroup\$
    – tysweat
    Jun 13, 2015 at 20:16

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