Extendable Project

i have the beginnings of a project, and whilst i await my parts to arrive I have a query, which on its basic level is easy, but i wonder if i can extend.

so i have a pcb1, [arduino / 8 leds / shift register / connector] and to this connector i add an exact carbon copy of pcb1

power lines flow through both pcbs through the connector

one of the lines in the connector of pcb1 is attached to an arduino pin that sends the output HIGH message, and on pcb2, it looks for this output (technically its looking for input HIGH, and if it finds it, it runs the pattern.

so if i have have 1 pcb connected, the pattern runs on 1 unit, if 2 units are connected, then pcb runs the pattern also.

so…

assuming that pcb1 is the master and all others are slaves… how can i work out how many slaves are connected to the master… is this even possible?

apart from the simple 1 line to show HIGH or LOW,
or to use a call/return or a detectable pulse
or multiple lines to send different patterns (obviously not “sending patterns” but triggering previously coded patterns

i haven’t started code and i haven’t started schematics… i’ve just ordered some tiny85’s, some mega328’s, some ir sensors and leds.

dammit, am i oversensing what i need to do?

should i just run a load of shift registers on the slave circuits...

kelvinmead:
should i just ...

You haven't said what you're trying to achieve, so it's hard to advise you how to do it.

Are you connecting all your slaves to board 1 (in parallel) or are you daisy-chaining (in series) them?