I have been trying to reverse engineer a ceiling fan remote control receiver to work with a Raspberry Pi Zero W. The light portion of the fan was easy enough to control, but I can't figure out how to control the motor. From what I've been able to figure out, the motor has 3 speeds and runs on 120v AC at 60hz. Here is a picture of the motor controller that I've extracted from the motor:

motor controller

Here is the cover in higher resolution:

cover zoomed

Here is my current schematic:


What should I use to control the motor that can be controlled by a Pi? It could either be pre-built (as long as it's not too expensive) or hand-built.

  • \$\begingroup\$ Your fan motor will not have a three-phase motor - I suspect that it is a three speed motor. \$\endgroup\$ May 5, 2020 at 19:44
  • \$\begingroup\$ The diagram for controlling the relay will cause the RPI to get burned up, also, instead of trying to make a new motor controller, you can instead modify the controller to take a signal from the RPI. Can you provide a picture of the remote controller and a general overview of the system layout. Maybe also some high resolution images of the controller board front and back. \$\endgroup\$ May 5, 2020 at 22:59

2 Answers 2


The remote control receiver is marked "Capacitor Fan speed Control." I expect that it has provisions for selecting a low, medium or high fan speed. I expect that is done by connecting the yellow wire to the black wire through a low-value capacitor, a medium-value capacitor or both capacitors in parallel. If that is the way it works, you need to find those two capacitors or two capacitors in one 3-lead package. Remove them or it from the controller and get two relays to connect them with your system. You will need a third relay to turn the fan on and off.

See also my answers to these two questions:

Varying run capacitor for speed control of single phase motor

Calculating the capacitor values to control ceiling fan speed

  • \$\begingroup\$ Looking at the board, there are 3 big capacitors. Two of them are 5uF 250v as well as one 1.8uF 250v under the transistor heat sink. This leaves an extra capacitor that may be used for the circuits or the lamp, but I'll look into getting one of each for the fan. \$\endgroup\$
    – ImTheSquid
    May 5, 2020 at 20:13
  • \$\begingroup\$ Capacitors for the fan will be non-polarized and likely less than 5uF. If they are not in the controller, there may be just one in the fan and the controller is providing variable voltage. You need to be sure what you have before putting something together. \$\endgroup\$
    – user80875
    May 5, 2020 at 22:00
  • \$\begingroup\$ The capacitors aren't polarized, but the fan does have a pull string, which may be controlling the voltage. The fan only goes as fast as the pull string's highest position. However, the problem is that the controller is stuck on the highest setting and I don't know what voltages I need. \$\endgroup\$
    – ImTheSquid
    May 6, 2020 at 1:02
  • \$\begingroup\$ The pull string is probably switching capacitors inside the fan. That means that the yellow wire and the white wire are connected to the fan. The controller is reducing the 120 VAC voltage with a traic. That means you either must build or buy a triac AC voltage controller or use relays to duplicate the pull-chain switch function. \$\endgroup\$
    – user80875
    May 6, 2020 at 1:32

Well, I can tell you what the wires are doing. Black and white (lower) are AC supply (phase) and neutral (which is NOT ground) from the supply/switch.

The upper wires are

  • White: neutral shared by both lamp and fan (certainly both tapped and passed thru).
  • Blue: switched power to lamp

  • Yellow: switched power to fan. Clearly they are modulating that power line in some way to control fan speed.

Safety ground is also wired, but bypasses this module entirely, so no wire for it. ETL approved this and gave it the equivalent of a "UL Listed" stamp, based on the guidance in the UL White Book.

Honestly, given the "playing with mains power" aspect of this, and the fact that 1000 different smart fan+light controllers already exist so you're reinventing the wheel, I don't feel like this is a good thing to do except as a "prove you can do it" experiment. But this is not a starter project.

As an experiment, feel free to use ЯU-Recognized relays. As a "I plan to use this indefinitely" thing, you must use UL-Listed relays, i.e. they have a UL in circle mark with a C or US sidemark, which will be weirdly more expensive and provide appropriate wiring methods for integrating into mains wiring.

There is nothing wrong with improvising low voltage control of mains appliances, as long as you use UL-Listed (not ЯU) relays, and install the mains side using NEC wiring methods. Mains is a whole different world that must be respected. We talk a lot about it over on diy.se.


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