I luckily don't have to imagine it. During an electric course in school for half a year where we learned all kinds of stuff like high voltage circuitry, we also

I luckily don't have to imagine it. During an electric course in school for half a year where we learned all kinds of stuff like high voltage circuitry, we also learned pneumatic logic. Almost all electric components can be replicated in pneumatics; capacitors, resistors, transistors, diodes (including Zener diodes)... And from that you can form simple logics. One design we had to generate was to build a pneumatic gate which would open and close by pressing four buttons (two for each side of the gate) and light up a red, yellow or green light depending on whether or not the gate is moving (of course the lights use a pressure sensor). Of course nobody builds that because such a system would be expensive compared to a Attiny with a shift register and a few relays capable of doing the same.