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Step 18: Motor Control #4 - Zero Cross Detection

Picture of Motor Control #4 - Zero Cross Detection
Zero cross Detect circuit.png

Mains AC is a sinusoidal waveform and the the Arduino needs to know the point at which the AC voltage crosses through 0V - the 'zero crossing'. The Arduino needs to know this to properly time when to trigger the triac’s firing action.

This document describes a simple zero cross circuit and why we want one:

In the circuit I made we use a cheap little PC816 optocoupler to isolate the arduino from the mains voltage, which is a somewhat safer method than that used above.