I'm working on a little project in my physics lab.
We would like to create a photon coincidence counter. We were thinking to use the Pi GPIO pin to monitor a couple of photo diode which produce a 15ns 5V TTL signal (I know the Pi can handle 3.3V maximum).
I asked on the RaspberryPi stack exchange (here) if the board could detect such short pulse and they suggested to use "GPIO Asynchronous Edge Detect" (they also suggested to ask here because it seemed a more specialised question).
I think this could work but I would like to know if the pin has some kind of "down-time" after being triggered where the pin doesn't register anything and if it doesn't at wich rate can it count?
I also would like to know if the board can read multiple signal of this type in short delay one with another (or even better simultaneously).
To make it more clear we are not trying to measure the duration of such pulse but only if two pulses from two different photo diode arrive on the Pi simultaneously.
I'm pretty new with the Pi and I hope i explained clearly the problem. This is more a proof of concept to see if it can be done, even if we need to go "bare metal".
Thanks
Best Answer
It would be better to use an external counter for this task rather than trying to manage all the complexity inside the Pi to make it work and guarantee that it works. You can read the output from the counter on the GPIO pins of the Pi.