I am working on a test automation project and currently have my main code on the Mega 2560 (with a 5'' display) and jam detection code on the Nano.
I had them communicating via SPI (nRF24L01+) before, but recently it was decided that the detection is an optional, not essential feature, and if needed the detector module (Nano with light barriers) could be connected directly to the main PCB with the Mega. So the wireless modules are scrapped.
I could completely remove the Nano and connect the light barriers directly to the Mega analog pins, but then I have a problem of them floating when no light barriers are connected.
Is it safe to connect two digital output pins on the Nano to two digital input pins (defaulted to LOW) on the Mega, with the Nano using the same 9V power as the Mega?
9V is coming from a buck converter (12V input, 1A max). I have a few more buck converters, so I could power the Nano from a separate one if 1A is not enough for Mega + Nano.