Soldering Through a Medical Stereo Microscope with NTSC Camera Assist

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Tuesday is my project night to work on Arduino and other electronic things with my old friend Bob V. He’s always had a great home workshop and occasionally he runs across interesting equipment to put in it. One recent item is a Brazilian-made Zeiss knock-off wall-mount stereo microscope. With a 250mm focal length, I believe this model was favored by dermatologists for its reach and coverage of different areas on the patient. As I understand it, they are no longer favored for their size and weight and are being replaced with something newer and much smaller.

Bob came into one of these a few months back and mounted it on his workshop wall, but if you try to imagine how far your arms have to stretch to look down the eye pieces through a rather tall instrument where the lens on the bottom is still 250mm (10 in.) further away, you can see how difficult it is to solder something while keeping it in focus. Tonight, Bob showed me the video camera and camera adapter tube that was recently found in a dusty drawer where it’s been since someone tried to tear off the 12-pin Hirose connector. We figured it was a standard connector, and a few minutes of digging on the Internet proved it was so. Unfortunately, the cheapest ready-to-use 12V PSU with that connector we found was $75, too expensive to risk purchasing for a camera that might have been broken by an old impact with a wall.

Undaunted, I opened the case (4 screws in back and 4 in front, and no funny business with “special” fasteners) and from the weight of the PCB traces coming from the connector, figured out that most of the pins carried signal not power, but the power pins wouldn’t be difficult to nail down. A few more minutes on Google revealed a camera datasheet for a different camera with a pinout on the second page. Moments with a continuity tester matched the camera well enough to the diagram that we felt we could feed +12V in on pins 1 and 2 (how simple!). Bob pulled out a 12VDC 500mA power supply and I tacked red and black wires to the appropriate places on the connector and ran them out an access port on the top.

We plugged it all together and ran an S-Video cable to an early 15″ LCD television he uses for testing video cameras and got some stunning results.

Microscope view on medium power Microscope view on high power Microscope view on max power

There’s one more setting for the internal lens carousel – it’s a rather wide view that’s good for looking for surface defects but not particularly useful for soldering or inspecting SMT solder joints.

I have a stereo microscope of my own that I made portable by replacing the back rest on an old broken office chair with a wooden adapter mount that could take the weight of the scope. Unfortunately, I still have the “long-arm” problem of trying to look through the eyepieces and while trying to reach the board under the lens with my tools. Perhaps I can find a replacement lens with a slightly shorter focal length. For now, though, I’m happy to use the wall-mounted microscope at Bob’s for a little “SMT TV”.

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