I want to perform the same operation on 20 Pis exactly at the same time. What I am currently doing for 3 Pis (and a master) is
I have a master Pi that says when to perform the operation
And three slave Pis that perform the operation
There's a wire from a GPIO output pin in the master that sends a signal
The same wire goes to an input GPIO pin in all three slaves
When they receive the signal (or the signal disappears), they perform the operation
Everything is working flawlessly, but is this scalable? If I put together 20 Pis instead of 3 (40 cm far each one from the next one), will this still work? Or will there be voltage or other electric problems?