Can a sign ppm 5v damage the arduino due pin?
The safest option is to ALWAYS assume the answer is yes!
I would never attach 5V to an 3.3V Due, just as I would never attach 7.6V to an Uno. My understanding is that Uno's internally have 1mA clamp diodes on their pins tied to the power rail and ground pins which will offer some protection, but not much. I don't know if this is true for all Atmel microcontrollers including the Due -- does any else reading this know if this is true?
[Edit: Even the Arduino site says it is a bad idea http://arduino.cc/en/Main/ArduinoBoardDue
with the line "Warning: Unlike other Arduino boards, the Arduino Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board."
anyway i use something to protect it. thanks.
I applaud your decision...it is the wisest choice.