The most significant part of your question is "voltage I do not know"! I'd suggest you never plug anything directly into any Arduino pin, unless you are absolutely sure you know exactly what it is.I have been working on reading and generating PPM signals for the last two weeks using the Uno -- my Due is on order. But even with the Uno I have been protecting the pin by having the PPM signal going through a voltage comparator (LM339). This has allowed me to read the PPM signal from my Spektrum DX6i's trainer port. I plan to use the same setup with the Due when it arrives as the LM339 can be powered by 3.3V.You could use a simple transistor circuit to protect the Due's input pin, but definitely use something to protect it.
Can a sign ppm 5v damage the arduino due pin?
anyway i use something to protect it. thanks.
A 5v pwm signal with a period of 20ms and 50% duty cycle behaves as an analog signal 2.5 v ... from there my doubt whether a PPM or PWM 5v signal ... really would harm pin or not.
Quote from: gorgonas on Jun 02, 2013, 11:09 pmA 5v pwm signal with a period of 20ms and 50% duty cycle behaves as an analog signal 2.5 v ... from there my doubt whether a PPM or PWM 5v signal ... really would harm pin or not.The concept you are describing, the DC equivalent voltage of an AC signal, applies to driving DC motors. I have used this myself both in class and at home. But, I would not apply it to anything else. Consider any voltage, AC or DC, over 3.3V applied to a Due pin as bad! It just isn't worth the (expensive) gamble. Edit: BTW, I'm happy to share code and schematics for the PPM generator and decoder sketches...well, once I get them ported to the Due from the Uno. If this will help you?