Originally Posted by midelic
How much is your original PPM input voltage(before reducing it)?It was one thread here around saying if PPM voltage is more than 3.3V it will fry the module.
im surprised to hear thierry cooked his pic with 10k resistor. i was certain there was not a ppm interface problem that cant be fixed with simple series and/or pullup resistor until hearing that. the avr guys have been discussing this for years and consensus is 200ohm resistor will protect modern mega and tiny devices from latchup or clamp diode damage even up to 12v. ive pretty much verified this myself shipping hundreds of chips with nothing more than 1k resistor in series for 12v rs232. no zener or other components needed.
i do know the old 90sxxxx avrs would latch and cook if you powered down and up again with 12v inputs even with 2k series resistor. so atmel fixed that long ago and im surprised to hear microchip hasnt. guess i should stop making fun of the guys who build those complicated level shifters and protection circuits.