Why a USB switch interface?
My wife is an itinerant teacher who works with kids with special needs and she had asked me to try to find a way to create one of these interfaces. I originally declined, as I had never done any soldering before, but after she was persistent, I decided to give it a try. Apparently it works great.
How much does it cost?
Excluding equipment costs (all set with my new soldering iron now), I put this together for between $10-15.
Step 1: Materials
USB mouse (Picked up one from Walmart for $5. Brand was "Onn" or something like that)
3.5 mm audio jack (These come in a pack of 2)
Solder (Mine came with a kit I bought. It not sure the exact size but it was approximately 3/4 of a mm in diameter.)
6-10" of braided copper wire (Mine was salvaged from an old Dell power brick)
Philips-head Screwdriver (Or a multi-bit)
1/4" drill bit (Use with screwdriver, or in a drill)
Step 2: Take Apart the Mouse
NOTE: Be very careful removing the housing as with this brand the front it held down with small fragile plastic clips. I broke these clips and had to later glue the housing down with crazy glue. This problem is solved by using more expensive usb mouses which are held together with more screws rather than plastic clips. When I say more expensive, that is relative...I have since completed this project again with a $12 mouse and it was held together with screws...much easier to deal with...