How would you do this?

[ERMEGM]

Hi Guys,

I am trying to trigger an input on a PIC16F687 using an external 12 volt source. The circuit will be using this same supply. Would you have the 12 volt source control a transistor which the transistor will be connected to the input of the pin (either pull up or down, haven't decided yet) or have the 12 volt source go to the input pin via resistors?

I thought about doing it via directly to the pin using resistors, such as in a voltage divider setup, but wasn't sure if that was the best way. Your thoughts?

Thanks,
Tony

[Charles Linquis]

A voltage divider on the input will work fine. How about 5K from the input pin to GND and 7.5K from the input pin to your 12V source. If you need a little noise
immunity, you can add a .1uF cap across the 5K resistor.

[aratti]

I would suggest optocoupler as TLP504 or similar.

Al.

[ERMEGM]

I would suggest optocoupler as TLP504 or similar.

Al.

Hi Al,

Just out of curiosity, why would you use the optocoupler?

Tony

[aratti]

With optocoupler you will obtain Total isolation from the 5 volts rail and total immunity to noise.

Cheers

Al.

[MikeWinston]

Actually the picbasic pro manual shows under the serin command, you
can input 12 volts directly through a current limiting resistor. (22k in example)

But if you truly need a reliable trigger, without false triggers, I agree with aratti
and use optocoupler and caps.