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I'm working on modifying my ICICLE boards to allow them to use dimming. I'm having trouble getting the circuit for the zero crossing detection to detect 120Hz. Instead I'm only getting a high enough pulse on the rising edge of the sine wave to detect 60Hz. The zero crossing circuit that I'm using is the same one described in the RENARD documentation and it is also on many other places on the web. One thing that I have noticed is that the output voltage varies highly (shifts up or down a volt) with a small VCC change (say 4.5V to 6V). A picture of my circuit is below. Also, I have attached a scope image showing the output signal (blue) and the input sine wave measured after the two 15K resistors (red). Does anybody have any tips or hints that could help me detect all 120 zeros in my wave?
The input voltage looks good; it should be around +/- 1 volt. The output is way too low and because you’re saying that the level is drastically changing with VCC, I would say that the H11AA1 is defective.
When you get this working, you may need to change the value of R1. It was chosen to match the input current of a PIC micro.
BTW, the first time that I tested this circuit, I only use 24VAC as the input voltage and it still functioned correctly. I’ve had enough first time circuits explode at 120 volts that I would prefer that they only smoke at 24.
____________________ No really... Just one more light and I'll be finished....
Disclaimer: If you take any of what I say as non-constructive, it's not how I intended it.
