I am looking for something like a multiway "relay dimmer". Which lets me dim a light using an Arduino and a manual dimmer. Schematic

(The manual dimmer should work without any computer!)

  • The big black 'dimmer' symbol - are you intending to build this too? If so, what load is it driving - AC? DC? Mains (230V/110V)? Sep 9, 2015 at 12:50
  • @CharlieHanson yes. It's a 230V
    – cocoseis
    Sep 9, 2015 at 13:06
  • Then first look at how AC dimmers work. Using a triac as the dimming device (the simplest form) requires the controller (Arduino, rotary potentiometer, cycle-of-the-moon detector, etc.) to send a pulse at a specific time to the triac to make it conduct. Typically the power for each controller is drawn from the AC itself, so you'll have to consider this for your 'manual' controller, assuming the Arduino is powered via USB. Sep 9, 2015 at 13:15

2 Answers 2


You could use a rotary encoder for that purpose!

Basically the rotary encoder is a knob that, for every "tick" you give it, it returns a different value to your Arduino. With a bit of programming you can sense the direction of the turn, if it is positive then you lighten up the LED, and vice versa.

I used that to control a RGB led, it works very well! here some more information on the rotary encoder and the code needed to use it.

  • But then the manual device would have to be connected to the Arduino and wouldn't work without it.. Right?
    – cocoseis
    Aug 31, 2015 at 13:07
  • Yes, I was thinking that Arduino itself can act as your dimmer. Maybe I got your question wrong though, so you need the whole system to be able to work without an Arduino?
    – Luca
    Aug 31, 2015 at 13:47
  • Correct - the Arduino is just a needed feature.. That's why I called it "multiway"
    – cocoseis
    Aug 31, 2015 at 15:16
  • 1
    I don't quite understand this. You may or may not have the Arduino there? Why not? Will someone open up the wall plate and remove it? Is the general idea that you turn a knob if you want to manually change the lighting, but under Arduino control (eg. at night) the Arduino will dim the lights on its own?
    – Nick Gammon
    Aug 31, 2015 at 22:20
  • 1
    Yes ... but it shouldn't fail. I mean it might, but I've had light dimmers fail before, and they didn't have Arduinos in them.
    – Nick Gammon
    Sep 3, 2015 at 20:43

I add another answer because I think I found something. After a few days searching on various sites that sell arduino stuff I found this http://www.dx.com/p/8-channel-5v-relay-module-extension-board-for-arduino-avr-arm-51-140703 that might be what you're looking for. One of the customers in the review states it can be used even without Arduino.

I know it's a relay, not a dimmer, but maybe you could add something to your circuit...

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