Retrofit a LED Ring to a Stereo Microscope

Build a LED tube to revive an old stereo microscope.

Stereo microscopes are awesome tools, to observe and inspect all kinds of small objects.

If you are lucky you can find some on ebay, in pretty in good shape and for decent prices. We are the happy owners of an old (but very good) one.

It is mandatory to have a good illumination of the observed objects. Ambient light is not enough, that's why they always include a lamp.

Our one had a tungsten bulb of another era, for which it's hard to find replacements, and which is not very bright, bulky, and produces an insane amount of heat.

So it was time to retrofit it with a commodity of this century: LEDs !

On the picture, you can see the old lamp, producing a quite poor spot on the object, and lot of lost energy. That's what we'll remove first.

These stereo microscope have their objectives enclosed in a large cone.

My one was more or less fitting inside a piece of PVC tube that I had on hand. So here's how I shaped the tube:

1. Find a coarsely corresponding chunk of PVC tube

2. Mark one end with masking tape, to delimit a straight border. On your oven's hot plate, use cookies wax paper, and melt the marked end to get it flat. You may need to do several attempts until you have the right temperature and exert the right pressure. If it fails, saw the end off, and retry. Repeat on the other end of the tube.

3. You may want to remove the excess, using a cutter/file and sandpaper.

4. With a jigsaw, make three slits, on one of the ends of the tube.

5. Drill a hole at the end of each slit. This will ensure the the slit will not propagate.

6. Fit the tube on the objective's housing, carefully using a hot air gun. If it is too tight, heat to release the pressure a bit; you may have to extend the slits. If it is too loose, bend inwards to create more pressure.

Add a LED stripe on the inner side, flush with the end without slits. Make sure that the connectors are on that same end of the tube.

I found a cute little Mentos tin, ideal for a switch box.

Also, I scavenged a jack socket and a nice angled jack plug, from some electronic scrap. I also got a nice little toggle switch.

With some putty I filled the side opposite to the lid, let it cure, then made a hole for the socket and a hole for the switch.

Time for the paint job.

To protect the inner side of the tube (esp. the LEDs) I used some masking tape.

It was necessary to make the PVC tube rough, using sandpaper, so that the paint would adhere on the plastic.

Then I spray painted the tube and the tin.

Time to solder and place the toggle switch and socket inside the tin.

I marked the place on the tube, and scratched off the paint.

Not to be forgotten: a hole in the tube and an aligned hole in the box, for the cables.

Then using some Sugru, I glued the box to the tube.

Through the hole in the tube and the hole in the box, I connected the LED stripe to the switch circuit.

I found an old 12V (acc. to the LED requirements) adapter, to which I soldered the jack plug, and protected the solder place by some heat shrink tubing.

After checking for no shorts with an ohmmeter: connect, switch on, and let there be light!

Now the tube can be fitted onto the microscope housing, and voilà, we're ready for optimal observation conditions!

Note: as one can see on the photo, I added a potentiometer below the toggle switch, in order to tune the brightness.