I have a Pi 3b+ in a MIDI foot controller and part of the I/O is a pair of expression pedal sockets. After, ahem, getting the tip and sleeve round the wrong way, they are working correctly now.
But, during testing, I disconnected one while the system was powered up and it shorted out the Pi, which is now dead. The circuit feeds 3.3 V to the ring, which is connected to the pedal potentiometer, and measures the voltage off the tip (connected to the pot's wiper). When the pedal is disconnected, the plug temporarily shorts the ring (3.3 V) to ground. So I added a 150 Ω resistor on the 3.3 V supply wire. But I don't know if that's enough, and I'm not game enough to try it without being fairly certain I won't destroy another Pi.
Is a current limiting resistor enough? If so, what value is "enough"?
Or do I need something more complicated to protect the Pi?
I don't know exactly how long the short lasts for, but it's well less than a second in practice.
Note: The circuit has an switch in the socket, so I can add a little bit of extra resistance when the jack is plugged in. That way, I can detect the "unplugged" state (ADC reads full 3.3 V) and max plugged voltage 3.1 V as separate states.