I'm trying to understand how to calculate the right value for resistors R1 and R2 in this circuit using the 4N25 optocoupler, and with 12Vac.
With 12Vac, Vp is 16.27v.
In this case, the optocoupler has a photo-transistor, does that mean that the voltage for the LED diode is 0.7v and the VCE for the transistor is 0.2v in saturation as a normal transistor?.
If that's right, then when V2 > 0.7v then the LED diode will be active with 0.7v, and the photo-transistor will be in saturation, with 0.2v in VCE, leaving 9.8v for R2.
But how to calculate the values for R1 and R2??