Converting Welch Allyn Otoscope & Opthalmoscope to “C” Batteries

Like many small New England towns we don’t have curbside pickup for our trash, instead we bundle everything up and take it to the town dump on Saturdays. This would seem like an inconvenience but, also like many small New England towns, our town dump includes a “Swap Shop.” The Swap Shop is simply a 20′ shipping container with some shelves in it where one can place “good” things for other citizens to take. To be honest, the vast majority of what is left in this Swap Shop is crap like broken plastic toys, VCRs, Printer/Copier/Fax machines (where the toner cost more than a new printer), and boxes of old cookbooks from the 70s. Though to be fair, my wife collects these cultural touchstones and intends to begin a blog on the topic soon. Stay tuned for The Cookbook Rescue League coming soon!

A couple of weeks ago I found a box of doctor’s office equipment including a set of jars labelled “Tongue Depressors”,”Applicators”,”and “Cotton.” These have been pressed into service on my workbench and the one labelled “Tongue Depressors” is actually holding it’s namesake.  Also in this box was a physician’s otoscope and an opthalmoscope. I played with then for a little bit and it was immediately obvious that they would be very useful in the workshop. The otoscope had a ring of fiber optic lighting that  turned out to be ideal for peering down the barrel of a 3D printer extruder. And the Opthalmoscope had magnifying lenses up to 40X and a light that projected indexed cross-hairs for comparing the sizes of things.

Both instruments were beautifully made of chrome plated brass with nickel-cadmium batteries in a handle that was meant to be plugged directly into a wall socket. Alas, the required batteries appeared to be peculiar to this particular instrument and the were rather overpriced.

Originally I was planning to replace the incandescent light bulbs with LEDs and build a “joule thief” boost circuit to power the scopes, but when I experimented with powering the otoscope from a couple of “C” batteries to see how bright it was I realized there was an easier way. One handle came apart into three pieces and it was a simple manner to cut a length of aluminum tube, in this case an old Electrolux vacuum clear wand, to extend the body enough to fit two “C” batteries.

The other handle was only two pieces, so I cut it in half with a hack saw. Once I figured out the length of aluminum tube, I wrapped aluminum duct tape around the handle to make a tight fit.

I was sure to fold a bit of the aluminum tape back on itself to make contact with the handle, the adhesive insulates. If the only tube you have is plastic or some other non-conductive material, just run a length of aluminum duct tape down the inside of the tube to complete the circuit.

If your are careful applying the tape you can make the fit tight enough so that the whole unit stays together on it’s own. In my case I added a little epoxy.

The result is a really useful tool that I utilize almost daily now!

Both devices were pretty easy to figure out, but the opthalmoscope includes a set of numbered settings in red that I have yet to understand. I believe that they are for use with a hand held lens, or perhaps they are for looking at structures with in the eyeball? I shall have to find a volunteer to find out!