I want to use one of the Raspberry Pi's GPIO pins as a shutdown signal to an Arduino. The idea is, that when the Raspberry starts up, it holds this pin high and when it completely shuts down, it leaves it floating (as is my understanding). I want to use this as a signal to detect the shutdown.
The circuit required should be fairly simple - I was thinking about only one diode to protect the Raspberry Pi from 5V accidentaly appearing on its pin and one resistor in series to limit the current and therefore lower the diode's voltage drop to keep the signal at a high enough level for the Arduino to be still reliably recognized as high.
3.3V signal ---l>|---////--- 3.1V signal still recognizable by Arduino.
The diode is BAT60A and the resistor is 2K Ohm.
But when I tried this circuit and applied 5V on the Arduino side, 5V appeared on the other side as well... I have a suspition, that this voltage will be 3.3V when I plug it into the Raspberry Pi, but I don't want to damage it, so I wanted to ask first.
Will the Raspberry Pi take any damage with this setup, if I accidentaly set the Arduino pin to high? And will the Arduino be able to detect the Raspberry Pi shutdown?
Thanks in advance for your answers!