If the jack is one third of the way in, the tip is touching the 0V contact and the ring and maybe the shield are also in contact with 0V. No problem there.If the jack is two thirds of the way in, the tip is touching the 5V contact. The ring and shield might be touching the 0V contact. I'm not sure if that is a problem or not. In theory, the PWM pin of the Arduino is high impedance, but on the other hand, it is at a higher voltage than the VCC pin, so current could follow back to the VCC pin, which is connected to 0V, or to the GND pin, which is also connected to 0V. But there is also a resistor between the jack tip and the PWM pin, so it won't be a short.But I think what you are saying is that just before that "two thirds" position, the tip of the jack can sort the 5V and 0V contacts in the socket? If so, there's nothing the Arduino circuit can do to prevent that, it would happen just the same with the potentiometer. Any protection will have to be done behind the socket in the mystery device, I think
This three-conductor jack has two isolated SPDT switches. They are activated by a plug going into the jack, which disconnects one throw and connects the other. The white arrowheads indicate a mechanical connection, while the black arrowheads indicate an electrical connection. This would be useful for a device that turns on when a plug is inserted, and off otherwise, with the power routed through the switches.
back on this again. Going around in circles.How can this be done.I have 5 volts coming out of an enclosure and entering another enclosure through a patch cable. The voltage needs to be current limited so that a user does not inadvertently short the supply as the patch cable and the various devices that can attach to it are designed to be plug and play and so it is quite possible that a user might plug something unexpected in, or do something to short the supply. At times the 5v is simply across a potentiometer, with the wiper feeding back to the other enclosure, and for that application the limiting resistor is not a problem. However, the five volts is sometimes used to power an op-amp and uC circuit (about 40mA total) that doesn't like working through the series resistor. What actually happens is that the output of the op-amp circuit , which is configured with some gain and a 2.5v swing around zero, starts to pulsate. The uC circuit seems to work ok, though I guess it is unstable.What about a charge pump, would that make any difference, or what else can be done.