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I have 2 raspberry PIs 1x PI3 and 1x PIZero with camera attached. I want to set up a system to have a output GPIO pin on the PI3 and a input pin on the pizero connect so that when I set the PI3 pin to HIGH, I can read it with the PIZero pin via interrupt and know when to take a picture.

Has anyone tried something similar or know if this would work well? I am testing at the moment and might be getting some false reading (need to do more testing). Using RPi.GPIO Library.

Most examples I've seen connected input GPIO to GND or 3.3v instead of another GPIO pin.

Edit: Would this also work for 1x pi3 to 4x pizero i.e. would 1 output pin on pi3 supply enough power that all 4 pizero can read it as input.

               <------> zero1 input pin
pi3 output pin <------> zero2 input pin
               <------> zero3 input pin
               <------> zero4 input pin
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  • Ah let me see. I would suggest to test looping mode first, interrupt mode later. (1) Config = Rpi A GPIO pin 1 output mode connected to Rpi B GPIO pin 2 input mode. (2) Toggle Rpi A GPIO pin 1 10 times, (3) Loop RpiB GPIO pin 2 to read 10 High and 10 Lows, and print results. (4) If looping test OK, then set Rpi GPIO 2 interrupt mode and test 10 interrupt prints. Counter suggestions welcome.
    – tlfong01
    Sep 18, 2019 at 5:41
  • Or you can skip the stupid looping mode test and start with interrupt mode test, and you can just use one Rpi to test out things. (1) Config = Rpi pin 1 set to output mode, same Rpi pin 2 set to interrupt mode, (2) Connect pin 1 to pin 2, (3) Toggle pin 1 a couple of times and see if pin 2 gets interrupt the same number of times.
    – tlfong01
    Sep 18, 2019 at 5:48
  • Actually I always prefer to use USB/UART serial. Two Rpis talk through serial, this way you can data log the messages with times etc. With parity checking etc, you can avoid false shuttering.
    – tlfong01
    Sep 18, 2019 at 5:55
  • Or you can consider the following "One Rpi + Serial Bluetooh Module + Selfie Bluetooth Shutter Module" configuration: (1) amazon.com/HiLetgo-Wireless-Bluetooth-Transceiver-Arduino/dp/…, (2) amazon.com/Premium-Bluetooth-Selfie-Control-Shutter/dp/….
    – tlfong01
    Sep 18, 2019 at 6:33

2 Answers 2

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No problem.

It is safest to introduce a resistor.

Connect any Pi ground pin to any of the other Pi's ground pins.

Connect any Pi GPIO pin to any of the other Pi's GPIO pins via a resistor (if you have one, anything between 300 ohms to 100 thousand ohms will do).

Set the transmitting GPIO as an output and the receiving GPIO as an input.

The resistor is only there to guard against setting both GPIOs as outputs to different levels.

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  • Just a single wire connection between input and output with resistor in the middle of the wire?
    – Lightsout
    Sep 18, 2019 at 20:30
  • @bakalolo That's correct. You also need the ground connection to complete the circuit.
    – joan
    Sep 18, 2019 at 20:33
  • I would like to use 4x pi zero input would this also work? Have 4 resistor 1 for each pi zero? I want to split 1 cable coming out of pi3 into 4 cables going into zeros?
    – Lightsout
    Sep 19, 2019 at 2:40
  • Yes, that should be fine. In a noisy environment like a drone I'd use a low value resistor if I used any at all. The resistor is simply there to mitigate against a short circuit.
    – joan
    Sep 19, 2019 at 6:35
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To comment on your new question the GPIO inputs are high impedance CMOS circuits and consume negligible power.

You could (in principle) connect a 100 GPIO inputs to 1 output - although this would be poor practice because of capacitive loading.

In fact, I would not use GPIO to connect multiple devices unless they are in close proximity and share a common Ground connection (with no ground loops). Even then you need to be mindful of interference.

I²C interconnection - which are effectively GPIO type connections do this and can be used to control ~70 devices, but use a low impedance termination (1.8kΩ) to minimise noise, but are only usable over relatively short distances.

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  • They are very close, im putting them all on a drone to take some nice pictures...
    – Lightsout
    Sep 19, 2019 at 6:15

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