The messy middle: PCB and Backlight Troubleshooting.

A project log for Kerbal Spaceship Potato

This is an input focused control panel for Kerbal Space Program.

Matthew PeverillMatthew Peverill 06/08/2020 at 22:020 Comments

So my makerspace is open again! Yay! That means I can get back to work. Unfortunately, lots of mis-steps. One problem is my PCB, which continues to be shorted out. I have fixed a lot of problems with it but at this point there are no visible manufacturing issues which makes me think there is something wrong with the design: not sure how to fix that. Maybe I will make a Kicad forum post later. In the mean time, let me talk a little bit about something I do know something about, which is how to make a back-lit panel (what I know about it is that it is a PITA). I've tried two approaches, with comparable results. The big lesson is: you need to test new materials with every size of engraving you're doing. Just because a setting works on your smallest text doesn't mean it will work on your larger engraved areas.

Attempt #1: Painting

Ok so for this approach, I took a sheet of 1/8" thick 40% transmissible acrylic sheeting, roughed it up with sandpaper, primed it, and then painted it with several layers of matte black spray-paint. Then I put it in the laser cutter and carefully tuned the settings to take off just the paint (see last post). The result is just ok:

Without backlighting, the text is hard to read because the contrast between the acrylic and the paint is not that high. Partly it's because the acrylic is gray-er than I thought, and partly it's because particles of paint become embedded in the rough surface where the laser engraves. You can see at the bottom where I tried to clean this out with alcohol: this dissolves the paint and makes it look worse. Also I'm not good at painting, so the surface is marred to begin with. With backlighting it looks better, but there is still some visible mess in the engraved areas, which is too bad (and also I'd like it to look good to the eye):

If I had used an adhesive to protect the surface, it may have helped. I also think I might have seen less powdery paint nonsense if I used a non-matte paint, but I have no evidence for this.

Attempt #2

Attempt #2 was a combo. First I used a 1/16" thick layer of 30% transmissable acrylic without engraving to serve as a diffuser (incidentally, doing this also means we can cut things like the anti-rotation for the rotary switches in to just this layer, which makes the whole thing neater):

Then a layer on top is reverse-engravable black and clear acrylic:

This stuff is really cool. You engrave on the back side, and then the top remains totally smooth because the engraving is on the bottom and seen through the clear layer. My tests looked amazing and I was really excited about it. Unfortunately, you can see that the settings didn't quite work. The small text is still hard to read (maybe a bit better than the last), despite extensive tuning. The larger engraved areas are actually totally burned away. I probably needed a bolded and/or larger font size and a lower power setting. Also, you can see some surface marring (I believe because the tape I used to protect the surface during cutting had air bubbles and may have caught on fire a bit). 

The backlighting does look a bit better, but still not quite spick and span:

Were I doing this again, I'd probably use the materials from attempt 2, make the text bigger, and reduce engraving power. I'm not sure I'm willing to shell out another $35 to do it though: we'll