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Here's an update with better pictures. Although I can't come close to a professionally-made keyboard, the results seem good enough for concept validation prototypes.My best results so far are with placeholders just the size of the conductive pills. I also found out the hard way that it's quite important to let the silicone cure completely in the mold, otherwise the surface is slightly slippery, and the pills fall off. I have not used them for any significant amount of time yet, so I don't know if they'll fall off anyways.Semi-transparent silicone works out OK for light guides and sight-signal keys. I used upside-down SMT LEDs (1208 LEDs that shine though a hole in the PCB. Everlight has them in 2-color, which come handy.)
I made a more elaborate version, where I had the mold and enclosure professionnally printed.The hardest silicone I could find was apparently 30 Shore. It's squishy by any standards, but apparently still usable.Mold design is another pain point. I actually ended up with a half-keyboard, because half the silicone slowly dripped out. My attempts at plugging the leaks were futile. I'm in the process of re-designing a mold where the bottom cavity would at the same time contain the fluid. Also, I bought conductive pills for the contacts; but they fell off and ended all over the place. I'm making the placeholders slightly smaller than the pills in my next iteration.My current trial is 1.5mm thick, with 1.5mm thick webbing and 1mm key travel. These values seem about right for casting silicone.
Analog Pressure-sensitive P...View Instructable »