Reading Multiple Gates on One I/O Pin

I am trying to read when the state of one of 8 photogates goes low by checking one I/O pin, the timing requirement of the system does not allow me to poll 8 pins sequentially. I would like to be able to set up an interrupt on one pin that would be trigger on a falling edge when any of the 8 gates goes low.

This may be a trivial question and an easy Google if I knew what the name of a device like was, but alas I do not. Can someone give me digital hand?



I'm not entirely sure what you are trying to do, I'm guessing use a latching parallel to serial shift register.

You may not need to do that, it is possible to read 8 IO pins on the Arduino simultaneously (well nearly), as long as they are on the same port.

An 8-input NAND.

erm, yes - I see what you mean, I completely missed the point.


The NAND gate was exactly what I was looking for thanks.


Why use a gate at all.

Use a 'wired or'.

Yes a diode wired to each device can be wired-ORed to create a single signal.