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AC Dimmer Circuit


Simple AC Dimmer circuit for incandescent bulbs. 128 levels of brightness. Parts are relatively cheap!

How it Works


  • Digital Signals. The four signals on the left. They are labelled on the board.
    • Yellow: light dimming signal, comes from Arduino digital pin 11.
    • White: zero-cross signal, goes to Arduino digital pin 2 in.
    • Red: arduino +5V supply.
    • Black: arduino GND.
    • The LED on board should dim or fade along with the AC light source. Fading will not work until AC power is connected, it depends on the zero-cross info from the H11AA1 chip.
  • AC Signals. The four white cords on the right. The bottom two cables on the right are the AC plug. The top two are the Bulb. These are labelled on the board, but are partially covered by the large screw terminals.
    • Bottom is AC Power - Neutral.
    • Bottom Middle is AC Power - Hot.
    • Top Middle is Bulb - Hot.
    • Top is Bulb - Neutral.
    • NOTE: For help identifying Hot and Neutral on lamp cord, look here.



Board Layout


PCB Files

Building the Circuit


 From a PCB

If you had some of these manufactured, then you'll want to build the PCB. See our tutorial on Populating a Fabricated PCB.

On a Breadboard




  • Make sure your Triac (T1, BTA12-600) is rated at high enough current for the device you are controlling. The product linked above is rated at 12Amps RMS. That's a lot of current!
  • Alternative TRIACs with different power ratings:

Alternative Design

Alternative SSR instead of MOC/Triac combination:
AC Phase Control (that's what we are doing):