Hacking Nikon cameras
Two-pin cable release connector
The first thing to figure out is the electrical interface for the simple, two-pin cable relase connector found on such cameras as the N2020, N70, and N8008.
This turns out to be very simple, indeed. Connect three diodes across the pins (in the correct direction, of course) in series to present a three-diode voltage drop, and the camera will spring to life. The exposure meter will come on, and the camera will attempt to focus if it’s set to do so.
If you then short across those diodes, causing the voltage drop across the two pins to drop to zero, the shutter will fire. If the camera is set to "bulb," the shutter will remain open as long as the pins are connected.
In fact, the MC-12B remote cable release does exactly what was just described, and I have drawn up a schematic of it to illustrate my findings:
The pin farthest from the plastic key/notch appears to be the chassis ground of the camera. The other pin is the signal pin and appears to be pulled up to the battery voltage. I’ve measured voltages at that pin between 4.40V to 6.12V, depending on battery freshness. Interestingly, the voltage on that pin is not switched by the camera’s main power switch; it’s always at battery voltage.
I have received a lot of email asking questions about the diodes in this circuit. The most common question is what kind of diodes they are. Naturally, the selection of diodes for this circuit will affect the voltage drop when just switch 1 is closed (the button is half-pressed). Perhaps the best way to determine this is to figure out what kind of diodes Nikon uses.
There are two likely possibilities. The diodes could be silicon, in which case the voltage drop across each diode would be around .7V, for a total near 2.1V. Alternatively, they could be germanium, in which case the drop would be around .4 each, for a total of 1.2V.
I suspect a circuit designed with either choice would work. In fact, there are people on the net who suggest using a resistor, instead, citing the complexity (?!) of the diode circuit. I don’t know what the voltage range is that will cause the camera to wake up, but not to fire the shutter, but ensuring that voltage drop of your device is similar to that of existing Nikon devices would seem prudent.
So, let’s measure an existing Nikon device. I have the Nikon MC-26, which adapts a 10-pin electronic control, such as the MC-20, to allow it to plug in to a two-pin camera, such as an N70. To measure this setup, I just connected it to a 2.6-ish V power source with a series resistor. When I push the button halfway and measure the voltage drop across the two pins, it reads 1.676 V. Right between the two postulated voltages!
If you happen to have a Nikon cable release and the ability to measure its voltage drop in the half-pressed state, please send me the measurements. Another useful thing to do would be to apply varying voltages to the camera interface and measure the points at which the camera wakes up and at which the shutter releases.
Ten-pin data interface
The next step, of course, is to investigate the rather more complex ten-pin datalink/cable-release interface present on the body of the N90, N90s, and F5.
I believe that two of the pins (the two at the bottom right, as you look at the camera) are identical in function to the two pin-interface described above. However, I am currently unable to investigate further (all my test equipment was stolen in a recent burglary), so I’ll have to refer you to a page which describes someone else’s discoveries. (That link has gone dead. Here is a copy I mirrored in Jan 2000.)
Well, more when I get more time to investigate. I will figure the thing out. :)