Got a project all together, really pretty (PCB, LCD, acrylic plate coming). Just one problem.
I have photo interrupters connected to the PCB with 3.5mm stereo cables and jacks on both sides. When I connect or disconnect the plug on the PCB side (rear is ground, middle is signal - high for unblocked interrupter, tip is supplying 5V to the interrupter), I get short circuits. Arduino powers off for a moment and windows makes the USB unplugged sound effect. The LCD resets to a row of black blocks. If I try to carefully remove the plug while forcing it on the side, sometimes I don't get shorting. I wonder if stereo plugs can get shorting just by themselves. But forcing it to lean on top or bottom sides will get shorting. Maybe I was doing something silly.
Parts I used: photo interrupter: http://www.sparkfun.com/commerce/product_info.php?products_id=9299
interrupter PCB: http://www.sparkfun.com/commerce/product_info.php?products_id=9322
The jack on the interrupter side is mounted on the side of a chocolate box never unplugged.
Just a side note. When I misconnected this interrupter (swapped 5V and GND), I did release some of the precious smokes residing in the interrupter but after the problem was corrected it still works fine (enough smoke left inside to function).
Thanks for replying!