Unresponsive Limit Switches

[rfry11]

On Sunday we hooked up our limit switches, which are essentially Vex limit switches set up to output to the Digital Sidecar's Digital I/O ports. I have them plugged into Digital I/O 1 and 3, and the colored wires are set up in this position, from left to right: White, Red, Black. We're using them to restrain the turret to a smaller degree of freedom. I have set up a very simple program that will tell me if the limit switches are pushed or not, I've attached a picture of the program. The problem that's arising is that the switches appear to be unresponsive, because they send no signal whatsoever. So, help?

By the way, sorry for the bad picture quality. Our Toshiba Satellite with a 2.5MB Trident Video Card is good at running Labview, but not so good at encoding pictures in 32-bit color

[nathanww]

Did you check the switches with a multimeter, and if so are they actually changing values when you press them?

[Kahn!]

We blew out the DIO channels on our sidecar last night, though the rest of the sidecar still worked. Try hooking up your second digital sidecar; you may have a similar problem.

[daltore]

This may seem like a stupid suggestion, but are you 100% sure that the limit switches are being pressed? Sometimes they can look pressed but not be contacting, especially if you're using the turret itself to activate them.

The VEX limit switches are SPDT type (single pole, double throw) meaning that there is a common line that is switched between the two other lines. I believe the common line is the signal (white) and it switches between ground and +5v, but don't quote me on that. I know that the closed state of the switch connects ground to signal. Just make sure all the wires are going to the right places for the digital sidecar, as these switches were designed for the VEX microcontroller, which has all of the DIO pins pulled high, so the configuration may be different.

Edit: The SPDT function is unused, signal is attached to the NO (normally open) pin and ground is attached to C (common). This means the circuit is closed between signal and ground when the switch is pressed.