Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2473089.
V3a Update 1/20/2018 Noticed the ribs in the top were a smidge off-center. Just tweaked it a bit, it should be center, or at least close enough
V3 Update 1/15/2018 Redesigned to support printing without supports. Top cover pieces combined and minor tweaks to shape. New printed "spring" secures with just a spot of glue. .stl files oriented to print without supports. Only 3 parts to print with V3.
All V3 parts were printed in PETG, .6 mm layer height (.8 mm nozzle) for prototyping. I'm not sure if the spring would work in PLA. The prototype works well, so I'm probably not going to try in .3mm, but I'm guessing it would work just fine in .3mm.
The top cover needed some reheating with a heat gun, to take out some warps in the sides. 5 mm holes in the top cover I needed to ream out for smooth operation.
I'll leave the old files in case anyone wants to use them still. The old version works like a champ!
I had a USB foot pedal, but it broke. So, I ordered another one. That broke too. I designed this one off the PCSensor FS1-P. The FS1-P uses an optical switch. Both of the ones failed, so I'm assuming some sort of reliability issue, at least under my use.
I used an SV-166-1C25 microswitch and springs from 4 clothespins. I used M3 bolts and nuts for securing the microswitch, and M5 bolts to secure the top to the bottom. The springs were krazy-glued into place, and the spring cover was hot-glued into place. The top cover plate was glued into place with modeling glue, and is optional.
I designed it with room for a keyboard USB interface module from a scavenged HP keyboard for use in voice chat in a video game (caps lock), but I suppose it should fit a teensy microcontroller or equivalent for something a bit more powerful. If you need just a simple footswitch, I think this could fit the bill as well.