Step 2: Wire voltage regulator
As mentioned earlier, here is the formula for determining what resistors you need for a an LM317 regulator:
(Voltage out) = 1.25 * (1 + (R2/R1))
Since we want apprx. 3v out I decided to use R2 = 150ohm and R1 = 100ohm which results in:
(Vout) = 1.25 * (1 + (150/100)) = 1.25 * 2.5 = 3.125v
3.125v is a little more than needed, but not enough to matter.
I'll leave the math to you if you need a different output (system of two equations anyone?)
Pick two wires that run through the cable to the phone and hi-jack them for your own uses : )
I picked the red and black wires, just because that makes sense for power and ground. Solder your chosen power wire to the output of your voltage regulator (see closeup image), and your chosen ground wire to the ground/outer pole you already connected to the voltage regulator. Make sure you cover any metal surfaces that may contact others with electrical tape.
Now, on the other end of the charge cable, snip off the old charger cable end and strip the wires you chose for your power and ground.