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Detecting and Timing the Zero Crossing and Power Frequency

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Miguel Gonzalez

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With a PIC17C43 I can perform the following:
Zero Crossing Detected?

set timer on how long the zero crossing is

Calculate Input Power Frequency

50Hz or 60Hz

Set pointer to 50 Hz table Set pointer to 60 Hz table

If I can make the above with a PIC12C508 any software samples or any other help from a good samaritan? Thanks... :(


New Member
If you use an AC opto isolator with a transistor output (found H11AA3 on Digikey which should work) with a pull up resistor on the transistor output (~10k for a guess) you should be able to connect it directly to a digital Capture compare input to time the length between crossings. This circuit should output a short negative pulse every zero crossing.

I think your pic has a capture compare module that is perfect for this kind of timing.



New Member
zero-crossing detector

Do you have access to the secondary of your power supply transformer (DC wall bricks won't work) ?. If so, a resistive divider or resistor/zener combination & a schmitt trigger can provide the 60Hz timing pulses. For timing, it's not necessary to have a true zero-crossing detector, you just need a circuit that gives you a consistent pulse on every cycle (duty cycle doesn't matter).
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