Maixium voltage on a input pin

[Acetronics2]

Merci Alain.

Ok:

- 2 parallel 5M resistors on the input pin (AN521 suggested a backup just in case).
- a pair of backup diodes on the input pin as well.

And now the noob question, the PIC will be powered by a 5V circuit, the signal from the sensor is powered on a 12V circuit, where do the backup diodes go to? The 12V cicuit or the 5V circuit?

The clamping diodes within the PIC go the the 5V circuit, I would assume the backup would go to the same place, just want to be sure.

This would greatly simplify my life 'cause it gets real complicated real quick trying to use op amps like the LM239, I got that idea from another tutorial.

Hi, Robert

No need for 5M if 12v signal ... just (say 45v ... automobile std. "power clamping" )

40v / 50µA .... 1M in series

diodes are - of course- between PIC input and power rails ( 5v and gnd )

IF using external clamp diodes, series resistor can be somewhat lowered :

using Schottky diodes ( Vf ~ .3v ) will easily allow 1 mA, (the internal clamping diodes won't have to conduct, then ... )

so, the resistor could be as low as 47k ... limiting input noise capture !!!

Alain