Problem with AC light dimmer circuit

Thread Starter


Joined May 7, 2010
I am making a wake up light alarm clock, but I am running into some issues with the light dimmer circuit. Here's the schematic (sorry, I didn't have a light bulb symbol):

The zero cross detector works perfectly, and I can detect it using my Arduino. I wrote a quick program to fade the light from 0 to full brightness and back and verified the correct output on my oscilloscope, synchronized to the zero crossing of the AC sine wave.

Here is a picture of the oscilloscope view, with the MOC3023 trigger on top, and the zero cross detector on the bottom:

Interestingly on the MOC3023M pins 6 and 4 are connected even when I ground the input pin 1, even though the gate should be disabled when there is no input on the other side (I forgot count of how many times I checked the wiring, and these 2 pins are definitely not connected). This results in the TRIAC's pins 1 and 3 constantly having 120v applied to them, which should trigger the gate and connect terminals 1 and 2 together, delivering 120v to the lamp. Surprisingly this never happens, resulting in a sad, unlit light bulb.

What's going on? Am I using the wrong resistor values? Is my MOC3023 and BT136 busted? Or both?

Here are the datasheets for the parts: