:tldr; Could problems occur if one connects a HIGH Output of one arduino to a PULLUP_INPUT of another while using differed power sources?
Hi I'm building some devices for a LARP Dungeon (think Escape room).
For that we have interfaces, riddles and switches(triggers). Interfaces provide access to sound/light/DMX sytems for riddles. Riddles check conditions and send state information to the interfaces.
To keep things simple, states are boolean (like riddle is solved, a critical mistake has been made,..)
I would like to use PULLUP_INPUTs on the receiving end so I can use simple switches to GND as controls. In some cases a switch might be connected directly to an interface. Mostly there is a riddle in-between. In those cases an OUTPUT of the riddle's Arduino will be connected to the PULLUP_INPUT of the Interface's Arduino. There will be multiple riddle Arduinos connected to one or even multiple Interfaces. Due to cable length, differed power sources etc. the potential to GND of the involved Arduinos might be differed. So I assume this difference will flow over the pullup resistor of the interfaces into their 5V. The internal PULLUP is ~20kOhms so current should not be a problem but can the voltage, which might be a little higher than the one of the input, cause problems?
Or would it be better to set the Output of a riddle Arduino to INPUT while the signal line should be HIGH so it gets a high impedance? Switching between: OUTPUT:LOW while active and INPUT while inactive.