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Basically I will have 3 Pi's running the same script to take synchronised photos. They will be physically very near each other, and I am looking into my options to trigger them at the same time.

My thoughts are:

  • run a simple flask server - this relies on network connectivity or to have one of the Pis acting as an AP and acting the initiator as well.

  • a single button or switch which can connect to GPIO input on all 3 devices - I'm not sure how if this kind of thing can be bought out of the box

Are there any other better options to do this kind of thing you guys could recommend?

  • Who/what decides when they take a picture? A person? A timer? Some external event? – Mark Smith Oct 18 '17 at 8:38
  • manual, person physically with the setup – chris Oct 18 '17 at 8:39
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I don't think you'll find anything much simpler than a switch connected to all three Pis. It doesn't need to be any special kind of switch, just a standard single-pole button. Set the appropriate GPIO on each Pi to input, pull-up. Connect together the appropriate GPIO on each Pi, and one side of the switch. Connect the other side of the switch to 0v. Make sure all three Pis are grounded together.

When you press the switch, all three inputs will go low.

Do whatever you would normally do to deal with switch bounce.

If the wires are very long, you could conceivably get noise problems causing false triggers. We can worry about that if it happens.

  • how would you recommend connecting the GPIOs? – chris Oct 18 '17 at 9:32
  • In what sense? Just a piece of wire. I'm not sure what you mean. – Mark Smith Oct 18 '17 at 11:28

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