Something I love to do is to take apart old, broken electronic devices and salvage parts from them. From many of these devices I get LEDs, and testing these can be very annoying if I don't have any 3V button cells lying around. I also occasionally use miniature lightbulbs for some projects or experiments, and they take quite some effort to test, because you need a holder. So I decided to make an LED and mini lightbulb tester.
I had planned on making this much earlier than now, but as you can see from the photos above, the first attempt did not work out very well. The wood (balsa) I used for it was much too soft, so precision was difficult, I used old wires and back then my soldering skills were terrible, so there were definitely some loose connections, or it was being short-circuited (it was dead within two hours), and I didn't have a battery holder, so I tried to connect two AAA batteries with tape and tin foil (didn't work out very well).
However, in this version I fixed all of those problems and improved the overall design. My new design was inspired by Instructables author Brennn10 and diyworkbench's LED testers.
Rather than making only one set of testing terminals for one LED at a time, I made several terminals, so many different types and kinds of LEDs can be tested easily. Some might have very short legs, for example. For that the large plates would be useful. Or you might want to compare some different LEDs, to see which one has brighter colors, for instance. Then you could plug them all into the female sockets next to each other. I also added terminals with a lower current, as some LEDs will burn out with only 100 Ohms. A 3.3k Ohm resistor did the job well.
Step 1: Supplies
- Fret or other saw
- Sand paper and block
- Soldering iron and solder
- Heavy-duty metal cutting scissors
- Scissors (or wire stripper)
- Insulated wire
- Wood varnish
- Double-sided tape
- Electrical tape, or heat shrink tubing
- Two-part epoxy
- Third Hand
- Mints tin - e.g. Altoids
- Wood - I think what I used was basswood, but I'm not sure.
- 100Ohm resistor
- 3.3k Ohm resistor
- Mini lightbulb holder
- Metal sheet (I got this from magnet packaging, but some metal from a can should work just as well)
- Wire connectors
- Female pin connectors (salvaged from an old PC)
- 2 AAA battery holder
Step 2: Casing
The first step is to prepare the tin. Use metal cutting scissors to cut out the inside of the lid of the tin. This part will then be replaced by a tablet of wood, or you could use any other non-conductive material. You just don't want it to conduct electricity, because it will short circuit your tester.
After cutting out the lid, make sure that the surface is even by hammering or bending down the cut edges, so the wood cover will stick to it.
Then, punch a hole into the side of the tin for the flip switch. Make sure it is at the right level, low enough for the lid to still fit on when the switch is installed. I used an awl to punch the hole, and to enlarge it I used a rough round file.
Step 3: Wood Cover
For the wood cover I used some sort of soft wood (I have no idea what it was, to be honest). Cut a piece that fits nicely onto the lid of the tin. Make it a few milimeters wider, just in case.
File it down so the edges are rounded like the edges of the tin, and the sides are straight. Then, file it down so the sharp edges on the top are rounded and smooth. Use sandpaper to smoothen it all out.
Plan out the locations of the various testing parts and plates on the wood cover, and cut them out with a fret saw and fine drill. Try to cut the holes as accurately as possible, so the parts will fit in tightly.
When everything is sawed and drilled out, use wood varnish to give it a nice and shiny finish. If the wood seems to roughen up the first time you varnish, slightly sand it again, then varnish again.
Step 4: Testing Plates and Sockets
Here's where soldering skills come in handy. Mines are by no means proficient, but I try, as you can see.
Solder wires to all of the various testing plates and sockets, and cut out the testing plates (cut out after you solder -- otherwise you might end up with some parts that don't fit in your holes or on top of the case properly).
Step 5: Wiring
Before you start to wire up all the connections, glue down the testing parts and the wood cover. I used two-part epoxy for this, but any strong glue should work.
Then, for the wiring. I made a few mistakes, so don't rely on the photos. Use the schematic instead.
The 100 Ohms resistor is attached to everything but the lightbulb. The lightbulb wouldn't work with 100 Ohms. The 3.3k Ohm resistor is attached to one of the sockets, and the two terminal strips. Those terminals will be used for any low-current LEDs.
Also, heat-shrink tubing would probably be much cleaner and more effective than electrical tape.
Step 6: Finishing
After finishing all of the wiring and fixing all of my connections, I had to fill up the space in the bottom of the tin somehow. I ended up using silicone, filling up all gaps with it. It makes great insulation, and isn't too heavy. It doesn't look too neat though.
And to make the wiring more tidy, I stuck down the connectors with double-sided tape.
Step 7: Done!
That's it! You're done with your LED and mini lightbulb tester.
As you can see from the pictures above, regular 3V LEDs will still light up with the lower current, but only very dimly. Usually the 3mm leds work better with low currents. You can also attach several LEDs in parallel, which is very useful for comparing colors or brightnesses.
Make sure to comment any suggestions, improvements, or photos of your own LED/mini lightbulb tester (I have some Pro Memberships to give away)!