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Would it be possible to connect one gpio directly to another gpio, and use one as input and the other as output on the pins?

Then I could just supply power to one of them and run them both headless. Wondering if this can be used in some way to cluster them together without the need to use ethernet.

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    Yes, but you will not get it to perform usefully at the same speed (100 000 000 bits/second). – goldilocks Jan 12 '16 at 19:47
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Sure, there's no reason that you couldn't connect one RPi to another via the GPIO pins. You'll have to work out some kind of protocol to pass messages, but that shouldn't be too difficult.

I would be careful about powering multiple RPi's through a daisy chained GPIO setup. If you have three RPis hooked up in a line, the first RPi has to deal with 3x the current it needs so that 1x the current reaches the final RPi. If you're not careful, you could wind up with a string of dead RPis.

  • awesome, the thought crossed my mind because I have 2 pi zeros, one with the standard pins soldered in, and the other with an angled header, so I can plug one directly into the other. I can't think of a practical use case, other than resource sharing or load balancing, but if I ever do.. – DWils Jan 12 '16 at 23:17
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    Wait a sec - if you plug one RPi Zero into another RPi Zero by just joining the pins of one into an angled header on the other, you are basically connecting every pin with the pin opposite to it (so pin 1 with 2, pin 3 with 4 etc.). I doubt this is what you want - it would connect 3V3 to 5V, P2 to 5V etc. In other words - Fried Pi. – Phil B. Jan 13 '16 at 3:58
  • @PhilB. uh... interesting... I didn't realize that's what he meant until his comment... – Jacobm001 Jan 13 '16 at 4:01
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    And even if you somehow manage to connect each pin to the same pin on the other RPi this way, you would still get output pins talking to output pins and 3V3 supplying power to the other RPi's 3V3 output .... I believe that you can power the RPi via the 5V pin (without overvoltage protection) but not sure the same works for 3V3. – Phil B. Jan 13 '16 at 4:02
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    @DWils: Better make sure you've got all pins correctly configured. Wouldn't want to connect two clocks, they're unlikely to be identical. And obviously you'd need to match input pins to output pins and vice versa. – MSalters Jan 14 '16 at 21:50

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