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The Great Vistium Video Hack

I came into possession of a Vistium XC75B/495 video camera, and I decided to hack up a cable arrangement and power feed that would let me drive the sound and video signals into a VCR. I didn't figure it would be too difficult - after all, I had hacked a personal computer videoconferencing setup into working with a VCR some time before. I figured it would be a fairly simple matter of figuring out the connector diagram and just hooking up the wires!

Alas, it was not nearly that simple.

The camera is a little toy about the size of a lemon that includes a nice color camera and microphone, and its only I/O is a single cable that terminates in a male 8-pin round plug. Here's a diagram of the plug - remember, you've got the wire in your hand and you're looking at the open end of the plug and seeing where the pins stick up:

     _    _
    |1|  |2|
  _     _   _
 |3|   |4| |5|
   _   _   _
  |6| |7| |8|

Pardon the really bad ASCII art; just visualize a circular plug with those eight pins poking out at you. The little gap in the middle row is just that - a gap, not a keyway or anything.

The camera came with a little leaflet that describes how to operate the features, and I was excited to see a pinout diagram for this cable on page 4! Here's what the booklet says about the pins:

The pin configuration of the connector is as follows:
Pin 1 = +5V (+-5%) power input Pin 5 = video out (CVBS)
Pin 2 = power ground input Pin 6 = no connection
Pin 3 = signal ground Pin 7 = no connection
Pin 4 = audio signal Pin 8 = signal ground

So, off we go! I cobbled up the cables, hooked up 5VDC, turned it on, and... NOTHING!

The power LED would not come on, no signals of any kind, nothing.

I checked and rechecked my wiring, the diagram, my connections, and everything else I could think of - I could find no mistakes, but the little camera just sat there like a stone. I finally abandoned the effort and pitched the whole mess back into the corner of the workbench, figuring the camera might be bad or something.

Ages later, I dug the whole mess out again and decided to try and find out where my earlier efforts had gone wrong. I checked and rechecked everything two or three more times, then hooked it up for a test - you guessed it, it failed again.

At this point, I figured the whole thing was a bust anyway, so I might as well resort to some more invasive procedures to try and figure out the problem. After a great deal of screwing around with the no-tamper screws holding the silly thing together, I had the camera completely taken apart on the bench. I was quite impressed with the circuitry; lots of surface-mount stuff and what looks like quite a bit of processing power on board.

On a whim, I unplugged the cable from the main circuit board and then used a continuity tester to chase the wiring from the round male connector to the circuit board connector. Imagine my surprise when I found that only four of the round male connector pins actually went anywhere, and on top of that, pins 1 and 2 were not connected to anything! (Remember, the diagram in the booklet indicated that pins 1 and 2 were the power feed!)

At this point, I realized that the diagram in the booklet was a bum steer. I went back through the booklet to verify that there was only one 8-pin mini-DIN plug diagram (there was) and that the model number associated with that diagram was the one most closely matching the model number of my camera (it was), thinking I might have just pulled some colossal bonehead move like wiring to the wrong diagram. No, no mistake on my part - the information in the booklet was just plain wrong.

OK, so now I'm really on my own. Four pins to work with: must be +5V, ground, audio, and video. All right, now which is which? I learned that pin 3 traced to three different actual wires in the cable, so I figured that pin 3 was a common ground for power, audio, and video. One down, three to go.

Crossing my fingers (remember, I all but wrote the stupid thing off when I opened it up), I hooked up the 5VDC ground to pin 3 and then fished around among pins 6, 7, and 8 with a live +5VDC lead until the power LED on the camera lit up. Not the safest or most elegant way to figure out the power hookup, but it worked. Now, I knew the purpose of two out of four pins. 3 was ground, and 7 was +5VDC.

I hooked up a hacked-off RCA cable to ground, plugged the connector into an old stereo on an input line, and then fished with the center conductor of the cable among pins 6 and 8 until I could tap on the camera microphone and hear the sound on the old stereo. Pin 8 was the winner - a line-level audio signal from the camera microphone. That left pin 6 as the obvious choice for the video signal, completing the circuit map!

I quickly made up the cable, incorporating two chopped-off RCA cables (audio and video), a power supply from the junk box that gave 5VDC, and a truly horrendous rat's nest of scrap wire soldered to a female mini-DIN jack that mated with the camera cable. My first test failed, and I threatened to fling the whole mess out into the street until I recalled that I had not hooked up the ground between the power supply/output cables junction and the camera connector. After feeling like an idiot for a moment, I made the last connection and brought the camera online with the VCR.

The camera works like a charm, doing all its fancy color balance, white level compensation, etc. and feeding a beautiful, clean, crisp line-level audio signal from its microphone. I'm thoroughly pleased with the result.

For your reference, here's the connector pinout table I came up with by reverse-engineering the cable myself:

The REAL pin configuration of the connector:
Pin 1 = no connectionPin 5 = no connection
Pin 2 = no connectionPin 6 = video out
Pin 3 = common groundPin 7 = +5VDC
Pin 4 = no connectionPin 8 = audio out

How could the booklet diagram have been that far off?

Why on Earth would two cameras in the same family (XC75B) have radically different, incompatible pin layouts (assuming of course that the diagram in the book is correct for the XC75B/460 and XC75B/465, the model numbers printed on the page)?

Who cares?

I got the little toy running with no investment other than some scrap cable and a junk power supply from my parts box, and now I can play around making 'home movies' in the basement with my VCR. If I really decide to get complicated with this thing, I'll see if I can dig up a panel-mount socket for the camera plug and make up a little project box that hides all the wires. For now, I run the thing through a nest of wires and a ball of electrical tape.

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