usb Shooter release cable: is a simple knob, which connects ground of usb cable with white one. if green one shortened to the ground, the pre-focus activated (the same logic as a main release button on the boby). There are No digital signals involved...
But, for some reason, i can not duplicate release cable via hand made one. That makes me creasy...)))
You can buy nx1 usb release cable on ebay for 10 dollars, and it is a fantastic little tool. I wish i could marry this cable with charging option...