I needed a way to switch the audio inputs to the speakers in my living room between the TV, phone, etc. After seeing 3.5mm (stereo miniplug) A/B switches online that cost between $25 and $40 — not kidding, look it up — the sensible thing to do was to make my own for about $8 (with 2x the capability).
All this takes is a 3P4T rotary switch and a few 3.5mm jack sockets. The first thing to do was to measure all the pins for connectivity, and diagram what went where.
The next step was pre-bending and pre-tinning the wires to fit on all the rotary switch terminals.
After connecting all the switch terminals (not shown), I bent the wires down, stripped them, and cut them to length against the audio jacks. The group of 4 together are the input jacks, and the solitary one is the output. I tried to line up the jacks to correspond to the positions of the indicator on the switch.
After testing all the connections, the next step was to cover it all in plastic. I heated ShapeLock (InstaMorph) to get the first few “tack weld” pieces of plastic to form a basic frame, then a much larger piece that I heated in the toaster oven (about 180F, on a piece of waxed paper) for the final touches.
When it came out, I pressed a USB key into the top in several places to make some places for labels to stick.
The final product looks ridiculous and works great!