ZCD TESTER

Notes: the voltage divider between R10 & R11 needs to set a midpoint voltage well below the transition voltage of the inverter ... otherwise it'll never switch don't forget fancy saturation calcs for the opto BJT either! size cap for delay. 1) size R10 + R11 for bjt 2) size R11 / (R10+ R11) to target transition voltage of inverter 3) size cap for delay