Thursday, April 21, 2011

Limit switches, part 1

The CNC3040 machine doesn't come with limit switches and having already crashed the machine once I thought it was high time to add ones. The problem is that the driver box doesn't have inputs for the switches. My first idea was to build a passthrough box to break out the input pins, but peeking inside the case I found a nicer solution.

Here's a closer look at the breakout board:

The unpopulated header on the left looks promising. Little work with a continuity tester revealed that the pins are connected via the bus buffer to parallel port input pins 13, 12, 11 and 10. (I don't know what the fifth pin is connected to.) Pin 10 is used for ESTOP, but pins 11-13 are unused. Each pin has a 4.5K pull-up resistor.

Pin header soldered in and mono jacks for connecting the switches

Almost done!

I tested the inputs by shorting the connectors and checking the pin statuses in HAL meter. Next step is adding the actual limit switches.


  1. Calle, thanks very much for documenting this stuff. I've just purchased the same machine and now I can add the limit switches too. Thanks again, keep up the good work.