I’m beginning to work on Panel 101, which will be one of the first completed control panels to be installed in the CM. Although the switches will be non-functional, the one gauge will be backlit. Using the same patterns for the round gauges described in an earlier article, I 3D-printed another set. I printed a needle on one transparency and a hub on a second transparency, and printed a scale on some plain paper. I cut these out and sandwiched them between some acrylic circles to create the gauge.
To make the backlight, I soldered two amber LEDs and their current-limiting resistors in parallel onto a small protoboard. I installed a pair of screws to act as terminals for attaching power, then soldered some leads between them and the LED circuit. I drilled a pair of mounting holes, and the circuit was complete. Similar backlighting would be needed for all of the other gauges, so I made sure to keep this simple since I would be making more of them.
I installed the gauge into the panel and aligned it in place with two screws. To provide additional depth for the LEDs, I added a second insert flipped so that its plate matched up with the other insert. I added a piece of tracing paper sandwiched between the two plates to serve as a diffuser for the light.
I fastened two of the screws with nuts, then started to install the backlight circuit. I slightly miscalculated the distance between the screws, and found that I needed to cut a little of the circuit board away to make room for the first two screws. Once this was done, the circuit mounted easily, and I secured it in place with some nylon locknuts. Yes, I know the circuit board is at a funny angle. It’s necessary so that the mounting holes won’t be right on the edge of the board. I probably should have bought the next larger size of protoboards, but these will still work fine like this. Nobody will see them on the completed CM anyway.
Before actually installing the panel in the CM, I wanted to test and see how the backlighting looked. I had breadboarded a dimmer circuit (see the article on the dimmers), so I connected the backlight board to it and applied power. The lighted gauge looked very authentic!