AC to PIC read hi or low

[Normnet]

A rectifier to change to DC and a voltage divider to bring it down to 5 volts should do the trick.

A problem can occur when power to PIC is off, the 5 volts from the divider can power the PIC.

Perhaps a simple transistor, 22vAC to 10k resistor to gate, collector pulls PIC input pin low?


Is this acceptable configuration?

Norm

[dhouston]

If the PIC you are using has clamping diodes on the inputs, all you need is a current limiting resistor in each circuit. There is a Microchip app note that covers this.

[Normnet]

If the PIC you are using has clamping diodes on the inputs, all you need is a current limiting resistor in each circuit. There is a Microchip app note that covers this.

This App? Interfacing to AC Power Lines

Norm

[dhouston]

This App? Interfacing to AC Power Lines

That's the one. It works with voltages from about 5.5VAC to ???VAC.

[mackrackit]

A problem can occur when power to PIC is off, the 5 volts from the divider can power the PIC.

You are correct. But you did not say that the PIC was going to be turned on and off. The voltage monitors that I have made are never shut off and equipped with backup power just incase.

Now that you know two ways to solve your first question and one way for the second. (this is a productive thread ) The most, I think, reliable way to isolate the PIC is an opto isolator. Nothing fancy, LED and a photo diode with a piece of heat shrink between them.