GRR, my project to make a hot plate controller for SMD soldering is NOT cooperating. I put together a simple schematic based on the reference design and had a prototype board made, but when I plug a lamp into the "load" side, it's always on. To test if there was a problem with the MOC3043, I pulled that chip--and the lamp still came on. I disconnected the controller input... lamp still on. I pulled out the 39-ohm resistor and C1, no change.
Cutting out R2 (330 ohm between A2 and gate) prevents the lamp from coming on, but then it never comes on. I feel I'm missing something hideously obvious. Halp? Schematics and photo attached; code is totally irrelevant at this point!
Note that the heatsink as shown in the schematic is probably on the wrong side (pin 3 should be gate; I think I made the footprint backward).
It's not even clear to me the best way to test this. I do have an analog scope, but since the lamp comes on even without the MOC3043 socketed, I must be missing something much larger. The large box is a 5v power supply to feed the AVR, but I can't see how that would cause any problem like this.