Stacking the Pi's or Ribbon GPIO to GPIO

I saw a picture of two pi’s attached via ribbon cable GPIO to GPIO, Is this a possible way to connect them? Or was that a very bad idea that makes the magic blue smoke ?

It wouldn’t be an immediate magic-blue-smoke situation, but I probably wouldn’t connect all pins because:

  • UART would be connected TX->TX and RX->RX which isn’t useful
  • The i2c pins would end up with two masters, which may or may not work depending on how skilfully you implement bus arbitration
  • Bad things might happen if you set a pin on a Pi to output and the same pin on the other Pi to an input. The only thing limiting the current flow between those pins would be their impedance so it could brown out both Pi’s at best.

Connecting a select few pins is a much more sensible approach, then you can design a communications bus that fits your needs and experiment with it safely. And unless you plan to do this anyway, there’s really no benefit to connecting them directly since it would just complicate matters and lead to contention over the pins.

What would you be aiming to achieve?

I have a Pi Zero with a burnt out USB port so it seems to be useless for anything except to insert into a project with a pre-written SD card set to function at start-up. Since without a USB I cannot hook much to it for input. I saw a picture of two Model B’s hooked up via Ribbon and after much googling I thought I would just ask.
Most my Pi Zero’s are soldered with a Extension type header so they have a female 2x20 header on the bottom as well as 2x20 male on the top. As you can guess, if they were stackable it would seem the easiest way to connect say a 4 node Pi zero compound computer. That would leave all the otg USBs open for use and no extra hardware would be needed. It was more a thought of curiosity. Plus I don’t know what to do with this Pi Zero that has connectivity to the USB but doesn’t work. It boots and everything, just USB does not recognize a single thing. My last thought is to Assign keys via GPIO much like the Astro-pi buttons in order to get a keyboard on it for use, but I really have alot more interesting ideas for other Pis first.