>Just endeavoring here and going off topic... >Assuming that the camera is digitally controlled, each >wire/pin may have a "0" or "1" value. The >shutter release has 3 states: no press, half press and full >press. Two (2) wires/pins will then do the trick, as this >gives 2^2 = 4 possibilities. >Like I said, just endeavoring as I have no inside Nikon >engineering knowledge... >
You still need a 3rd wire to act as a ground reference for those states
Also keep in mind that the 3 wire system was designed to be implemented with only mechanical switches, not some sort of digital circuit. It is not a "digital state", per se, but a bog simple electrical short or open - to that 3rd ground wire. In other words, the remote itself has no voltage source to impress a "digital voltage state" across the circuit. If it did, it would require either a battery or yet another (4th) wire to power the digital circuit
You could build a fully functional remote with two single pole single throw (SPST) push button switches, probably available at Radio Shack, 3 wires and a donor 10 pin plug. It would not be as slick as a mechanical single push button remote because a half press would be done on one switch, and a full press on another. But that's the principle. It might even be possible to source a generic single push button switch with two throw contacts but I don't recall ever running across one.
Technically, a remote is basically a single pole double throw (SPDT) momentary contact switch, where two wires connect to the two throws and the 3rd ground wire connects to the common pole. The switch is of the ON-OFF-ON variety, where "OFF" opens both wires.
You can actually buy those SPDT momentary contact switches off the shelf for about a buck a piece. The cost problem is the 10 pin plug unless you have a suitable donor. But I doubt you would find that switch at Rat Shack or a local electronics house (?).
A more easily made and more readily available DIY switch would be a standard SPDT toggle switch, better if it always returned to the central OFF position. It would still be cumbersome for a lot of situations.
As far as a "spare (4th) state", my recollection of diagnosing a problem in a Phottix remote was that on a full press, the half press pole remained shorted. This was "an accident" of the mechanical design of the switch, where the half press pole remains closed when the full press pole is closed. I assume the camera ignores the half press condition when it senses full press, allowing my hypothetical SPDT or a dual SPST switch to function correctly.
So while it is possible to have a 4th state condition with 3 wires, in practice it would require a mechanically more complex and expensive switch. Thus that 4th state is ignored.
Just continuing your "endeavoring"
But whatever the logic, mechanical or digital, you need a ground as a reference to the state of the two other wires.