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I am trying to communicate between 2 raspberry pi's (3B and 3B+), through Gpio's (not uart, just as input output).

So I am making a gpio on one Pi as Input and on the other Pi as output. So can I connect them directly via jumper and will it not affect or damage my Pi in anyway?

I'm too scared to even touch the Pi pins after I fried out an earlier Pi.

I am scared to proceed with the above way and I am stuck in my project.

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    Yes. To be safe you might want to connect their grounds (Pin 06) together too with a jumper. But that shouldn't be necessary. I've connected two pis by jumping the GPIO several times. Commented Apr 24, 2020 at 23:17

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The FIRST thing you MUST do in interconnecting 2 devices is ensure they have a common reference (incorrectly called Gnd - as the Pi will float wrt Ground).
It is also recommended to join Gnd FIRST - before making any other connection.

It is acceptable to directly connect 2 GPIO, but it is prudent to use a series resistor (~1kΩ) to protect the GPIO in the event both are configured as Output.

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  • What's worrying me is so much is, during boot up some gpio's will be high ! So what if both the gpio's on each pi that are connected go high, will go not lead to an exceeding voltage and damage the pi !?
    – Prajwal
    Commented Apr 25, 2020 at 10:09
  • @Prajwal As long as the grounds are connected you are extremely unlikely to cause damage by connecting GPIO from one Pi to GPIO on another Pi. To mitigate any possibility of damage have a resistor in-line between the GPIO.
    – joan
    Commented Apr 25, 2020 at 10:16
  • @Prajwal on boot all GPIO are Inputs. It is only prudent to use a series resistor to protect against both being configured as Output and set to different values.
    – Milliways
    Commented Apr 25, 2020 at 10:43
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You can increase the safety of the connection and mitigate grounding issues by inserting an opto-coupler (e.g. 817) between the output pin of one pi and the input pin of the other. Note that opto-couplers work in only one direction, so if you have an opto-coupler between them you can't reverse the communication by reconfiguring the pins.

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  • Perhaps you user297954 could add a example/schematic?
    – MatsK
    Commented Apr 25, 2020 at 12:18

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