Crackling sound when connecting camera to Raspberry Pi circuit
As far as I could find, the Prontor-Compur Flash Sync port seems to be a open drain or open collector setup (Or SCR Thyristor). It simply pulls the Positive line low when the shutter is triggered. I cannot link to any reliable source of this! But based on a few arduino projects online which work with a slave flash, this seems to be the case. It's essentially the same exact circuit that the hot-shoe uses.

Below is an optocouple based setup. If you really want the latch, then just place it at the node GPIO instead. I suggest powering it from the RPI's 3.3V supply, to make it easier. If it needs 5V, then the output needs a voltage divider as the RPi GPIO are NOT 5V compatible.







simulate this circuit &ndash; Schematic created using CircuitLab

Logic here is REVERSED. The Camera will trigger the node RPi GPIO to go low when the picture is taken.

I Highly suggest you measure the PC Port voltage and behavior first before connecting this as you may damage the Camera, or another RPi if I am wrong. Double check everything.