See What's Going On with Your CNC Using a Parallel LEDinator Diagnostic Tool

The parallel port is something of a relic of days past in the PC world, however, it still has its uses, even if it's probably not what's driving your printer. One place it's used is in some types of CNC cutting equipment, and after my CNC router mysteriously stopped working, I decided to do the "logical" thing and design a "Parallel LEDinator" diagnostic PCB.

The circuit here is in fact quite simple, with the PCB connecting a male DB25 input to another male DB25 as an output, effectively creating a gender changer that is needed for my particular setup anyway. In addition to this pass-through, 10K resistors are attached to each connection to allow a small amount of current through LEDs and to ground. This thus lights up the LEDs when signals are passed through, enabling one to visualize what lines are active at any one time.

Red LEDs are positioned to display input signals, while blue lights are set up to show outputs and bi-directional lines — though whether or not this works exactly as intended is something of an open question. In the end, extra blinkenlights are always fun, but one could also argue that it gives my process another avenue of failure.

I do think that this could be an excellent diagnostic tool in some specialty applications, and if there's interest, I may sell these PCBs in the future. KiCAD design files for the LEDinator are available on GitHub.

As for the router problem itself, it turned out I had a software issue with my controller on the computer side that was pretty easy to resolve. While largely unnecessary, it was a fun adventure in PCB design, and a great learning experience.