Digital Sidecar problem

Near the end of the day today, when we had stuff finally working like it was supposed to, we discovered a rather odd problem with one of our DSC’s. We have a limit switch that was hooked into the digital I/O 6 port, while most of our motors were being driven from the PWM ports on the same DSC. Well, whenever the limit switch was closed (linking signal to +5V), all the motors would stop, with blinking orange lights on the victors/jaguars. After finally tracking down the problem, we pulled out the PWM cable for that port and stuck in a new one, hooked up to a new limit switch (in order to determine if there was a short somewhere in the existing wiring) and saw the same problem. After looking into it a while, we noticed the +5V LED went off whenever that limit switch was pressed.

We moved the switch to a different Digital I/O port, and everything works just fine now, but i was wondering if anyone else has seen a similar problem with the DSC?

We had kind of a similar experience, my students couldn’t figure out why the code wouldn’t work, after looking at it long and hard, noticed that the 5V light on the dsc wasn’t on (all other lights were on) and the speed controllers only blinked. turned out that a piece of metal shaving had gotten into the dsc and somehow managed to short the 5v circuit.

If you’ve got your switch wired between 5V and GND instead of SIG and GND, whenever the switch closes, the 5V supply is directly shorted out and will essentially disable your Digital Sidecar. The 5V supply has short circuit protection for this very reason.

Switches need to be wired between SIG and GND (the two pins on the outer rows of the Digital I/O header). There is an internal (to the DSC) 10kOhm pull-up that will set the digital input to logic 1 when the switch is open.


We triple checked the wiring on the switch with the multimeter - we definitely are NOT shorting gnd and +5V - otherwise it wouldn’t start to magically work when we plugged it into a different port.

As mentioned above, if there is a metal shaving shorting the SIG and GND pins on that one port then when you close the switch it would short 5v and GND.