In my current project, I need to trigger multiple Raspberry PIs using one single wire. Triggering is very simple: 3.3v or 5v line going up or down every 2 or 3 minutes is enough. Devices are separated by a 20 to 80cm. The important thing is that all devices see the change at the same time.
First thought is to chain all devices using same GPIO pin and "listen" for a change on that pin. I know I could use internal pull-ups but would that be enough, for say, 50 devices ? I have the feeling that this won't work. What did I forget ?
EDIT: Thank you for your comments. You are right my question is unclear.
- All RPi are identical and all would wait for an interrupt on the same GPIO pin.
- All devices should see the change at the same time means as close as it can be. Time between the signal change and the last RPi to react should be less than 5 ms.
- Distance between first and last RPi is approx 6m.
As of today, my 50 RPi are connected using the spread toolkit and I am happy with it; although the RPi are now synchronized, the problem I have is the latency between the (software) trigger and the reaction from the RPi. Again, they all react at the 'same' time, but it takes too long to react (approx. 350 ms)
My goal using a wired trigger is to get an "instant" reaction as opposed to the software trigger. So my question is: how can I link/connect 50 RPi together with a minimum of wiring so that they all get interrupted within 5 ms ?
Thanks for any help, Julien