We recently came into possession of an old overhead projector - a Dukane Sunsplash 2123 Overhead Transparency Projector, to be precise. We're not in need of an overhead projector but the Fresnel lens caught my eye and there were a lot of other shiny things on it, too.
Step 1: Tools Needed
Needed tools will probably vary with your overhead projector model. But you'll need at minimum:
- wire clippers
- needle nose pliers
- glass cleaner for the mirror, magnifier and Fresnel lens
and keep the hammer nearby just in case a little gentle persuasion is needed.
Step 2: How It Works & What's Salvageable
Overhead projectors use a Fresnel lens and mirrors to project a magnified image from a transparent film placed on a clear platform onto a wall or screen. Overhead projectors are pretty straightforward devices, consisting of a set of mirrors, lenses and magnifier, a bulb in a reflective setting (with a spare bulb, in this case) , a fan to keep the whole thing cool and usually a pivoting or extending arm to adjust the mirror and magnifier, plus the electronics for the whole thing.
Recoverable Parts include:
- Lamp and Reflector- A pair of high intensity bulbs sit inside the big plastic base unit of the overhead projector, situated inside a reflector to direct the light forward toward a mirror. There are two bulbs because they burn our quickly, usually within 100 hours, and the second bulb is intended to act as a spare, moved into place with a simple twist of a knob.
- Fresnel Lens - This lens focuses the light into a cone shape, projecting the image on the transparency onto the magnifier and mirror above it and then to the screen clearly.The Fresnel lens on which the transparency is placed is used to redirect most of the light striking the image into a cone shape towards the focusing lens
- Fan – The lamp gets really hot, so a small fan keeps the who thing cool.
- Heat sinks - a couple of them in this case, in addition to the fan
- Magnifier – above the Fresnel lens base, on pivoting, adjustable arm, is big round magnifying lens through which the projected transparency image passes to the screen or wall.
- Lens - Between the lamp and the mirror in the base of the unit is a light condenser –an internal lens through which the lamp projects light to the transparency plate above.
- Mirror – Hinged for adjustment, there's an inside m and an external mirror reverses the projected image so it appears properly to viewers on the wall or screen.
- Fasteners - lots of nice little screws and washers
- Electronics components - capacitors, resistors, etc.
- Post Assembly - a nice pivoting, adjustable plastic arm
- Base unit - a nice big plastic base unit
Step 3: Free the Fresnel
A Fresnel lens is a thin lens that can be made of plastic or glass, and is unique in that it can capture and focus oblique light efficiently. You probably know them from lighthouses, but they also have applications as simple, cheap magnifiers to lay over books or other text.
Flat Fresnel lens like the ones in overhead projectors consist of an array of prismatic lenes arranged in concentric circles with steeper prisms on the edges, and a flat or slightly convex center.
In the Dukane projector, the lens is super easy to remove.
The lid of the projector simply unsnaps from the base. Flip it over and you'll see some little plastic tabs on the corners that you can just twist out of the way. After you free each corner, you can lift the lens right out of its frame.
Step 4: Clean & Use
Step 5: Mirror and Magnifier Salvage
The magnifier and mirror assembly simply unscrew from the base unit. And then you can further disassemble those. You can actually take the magnifier completely out its frame, but it's probably safer and just as useful left in it.
Step 6: Remove Post Assembly - Part 1
This ended up being the most ridiculously complicated part of the overhead projector salvage. While the top screw removed easily, the 2nd screw holding the pivoting arm to the base plate absolutely refused to budge. I sized up the inside nut and tried approaching the problem that way, but it seemed to be jamming up on a tiny ridge of plastic inside the unit.
Step 7: Post Assembly Removal - Part 2
I wiggled and wrenched, resorted to trying to tap a scraper between the arm and the base unit with a hammer, and finally took a file to the inside of the unit, to try to file off the offending plastic, which finally did the trick and I was able to remove the metal plate that turned out to be holding the whole post assembly in place.
Step 8: Freeing Lamp and Lens Assembly
This was pretty straightforward. The electronic innards of an overhead projector are simple and clean. Removing the lamp assembly amounted to removing the wire guards covering the wires, taking wire snips to the plastic ties holding everything together.
Step 9: Remove Cooling Fan
Removing the fan was mostly a matter of just unfastening small screws and some wires.
Step 10: Unplug Electronics and Unscrew From Base
Unplug from the power switch and adjusting knobs. Then the lamp and lens assembly need to be unscrewed from the base - a couple of screws underneath the base hold it in place,
Step 11: Salvage Remaining Electronics
What remains is a little collection of capacitors, resistors, wires, and small fasteners. Salvage at will!
Step 12: Treasure!
There you have it! Out of Dukane Sunsplash overhead projector worth about $40 on eBay you've got:
- Fresnel lens
- Small hand lens
- Magnifier lens
- lamp bulbs in a reflector unit
- a plastic pivoting post with an adjustable rachet arm
- a collection of fasteners
- a handful of electronics components and wires and
- a big plastic box
Value? Probably about $40!
However, from that collection of now individual parts, you now have a half dozen other usable tools like the lenses and lamps, and parts for other projects, as a well a very nice big project box that comes complete with a power cord and switch that you can wire stuff right into.
For our purposes at Eureka Factory, these are also educational tools that we can use for hands on activities and staff development training.
And the whole collection stores conveniently back in the box!