Light Dimming Circuit

Forum 2005-2010 (read only) Hardware Interfacing
1

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:
BT136: http://www.nxp.com/documents/data_sh...136_SERIES.pdf
MOC3023M: Intelligent Power and Sensing Technologies | onsemi
H11AA1M: http://datasheet.octopart.com/H11A1-...sheet-1835.pdf

Thanks!

2

triacs leak current even when the photo side is off. Enough to fool a high impedance meter. Or its output is shorted.. Attach the bulb and find out.

What wattage are R1/R2?

And of course...Use caution when working with line voltages...

3

and why no bridge rectifier for the ZC opto input?

4

I measured pins 6 and 4 on the MOC3023M with a multimeter against AC neutral, both showed 120V so I knew the gate on the MOC3023M was either open or they were connected in some other way. Turns out it was due to the way the BT136 was wired. Switching the wiring on MT1 and MT2 on the TRIAC fixed the issue I was having with it, and pins 6 and 4 were no longer connected on the MOC3023M. Who knew it mattered which way you wired MT1 and MT2 on the TRIAC up, I thought it conducted both ways? Now it looks like the LED in the MOC3023M is busted, can't trigger it no matter what size resistor I use, and a resistance measurement with multimeter shows infinity when measuring the LED in the optocoupler both ways.

I'm going to buy some more MOC3023M's and see if a new one will fix the problem.