Step 1: Materials & tools
(1) Hands-free cell phone kit
IMPORTANT: The DSLRs take a 3/32" stereo plug. See the picture for details.
(2) Momentary buttons (two colors)
(1) Mini micro switch
(1) Enclosure, for me a wonderfully ironic 35mm film canister
Drill & bits
Soldering iron and solder
Wire stripping tools
Mad Skillz (which you have, because you're cool enough to find this)
Step 2: Break open the mic
You may not get the same model kit, so some experimentation is required.
Inside the microphone box was a tiny circuit board hooked to 4 wires. I plugged in the kit to my camera for testing. Don't worry, there' s no current in these wires. I took my knife and shorted various combinations and observed the results. I found that two are ground wires, and the other two have functions:
By connecting the Red to a ground, the camera focused. Wonderful news.
We will now make button to do this work for us.