Can't get home!

fgauder wrote:

The servo drives have a built in feature that inhibits travel in the direction of the tripped limit.

Aha! Why didn't we think of that?

Definitely one to add to the "weird causes to remember" list.

alexr wrote:

My B.O.B. comes with a 1k pull up circuit for inputs such as limit switchs and e stop.
Im no electronics engineer so i am not sure why they need to increase resistance/impedance

Just for clarification, a pull-up doesn't increase the input impedence, if anything it reduces it.

The computer senses the voltage of the pin, but your external circuit typically works by changing the flow of current rather than applying a voltage.

The pull-up goes between the +5V and the pin, and then the limit switch goes between the pin and 0V / ground / earth.

Think of the resulting circuit as a potential divider. With the switch open there is 1k to 5V and infinity to 0V, so the pin sits at a nice, solid, 5V.
With the switch closed there is still 1k on the 5V side, but 0 ohms on the 0V side, so the pin is pulled hard down to 0V. (and there will be a steady 5mA running from the +v to 0v through the switch.

Without the pull-up and with the switch open the input pin is not connected to anything at all except the wire to the switch. This will tend to act like an antenna, and the PC will detect all sorts of random voltages on it.