LED / Mini Lightbulb Tester





Introduction: LED / Mini Lightbulb Tester

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

  • Drill
  • Silicone
  • Fret or other saw
  • Sand paper and block
  • Files
  • Awl
  • Soldering iron and solder
  • Heavy-duty metal cutting scissors
  • Wrench
  • Scissors (or wire stripper)
  • Insulated wire
  • Screwdriver
  • Wood varnish
  • Paintbrush
  • Double-sided tape
  • Electrical tape, or heat shrink tubing
  • Two-part epoxy
  • Clamps
  • Multimeter
  • 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)!



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    28 Discussions

    Hey sjroth! If the wood you used was very soft, it is more than likely balsa wood. If it was harder, it could have been basswood. Those are some of the two most popular craft woods. Very nice project!

    1 reply

    Yeah, it's most probably basswood. I know that it isn't balsa because my first design (see intro) was made of balsa, and that was much too soft.

    What a great Project!!.
    Well done, love the wood idea (I believe we call it Balsa woo in Australia) and I hadn't thought of using it for a project like this, I love it.
    The only thing I would suggests and that's only because I am an Electrician by trade is it would be great to use a colour coding with your wires as you would find it easier to follow by looking at it and more Lables to identify + and _ and Low and High Current.
    But hey I think it's a great job and I love it.
    I will be starting to do one as soon as I have finished my first Instructable that I am working on.
    But Great work Keep them coming.

    4 replies

    Thanks, I'm glad you like it. The wood I used definitely isn't balsa, it's much harder than that. More like basswood. Anyways, thanks for the wiring tip. Now that I think back to it, I wonder why I didn't do that. It would have made things much easier to organize and troubleshoot. As for the labeling, I will do that soon, as I told theboffin below.

    Ok, that's why I stated I hadn't thought of using it before as it is a soft wood, I am sorry for the misdiagnosis of it. I am no conocer on woods by no means, it does look very similar.
    So this Basswood is a lot harder, a bit harder, I only ask because I am interested in doing the project and you seem to have been able to manipulate the wood the way you want with the bevels and such.
    Anyway, once again well done I think it's a great project and it's on my next to do list.
    Take Care

    Here, I got some pictures. I bought this board in a japanese store that sells everything for about two dollars. They call it "Wooden Material", but I'm assuming it's something like basswood. It's quite soft, but also quite a bit harder and heavier than balsa. For balsa I don't even use a saw (craft knife works too), but for this I had to. I used a fret saw, which worked really well. I hope that gives you an idea.


    Thanks I will look into it.
    Take Care and I will be waiting to see what you come out with next.

    In the scheme is not indicated the metal plates. How they are related and what is their function? I like the idea of ​​using wood finishing. Sorry for my English, I used Google translator.

    4 replies

    Yes, if you look at the schematic, there are four pairs of 100Ohm connection points. One of those is those two plates. The plates could be used for LEDs with fat, bent, or very short legs, or as theboffin suggested, surface-mount LEDs.

    Thanks if you said now, in the scheme was not written. Good idea the use of test plates for other types of LEDs. Congratulations again.

    Surface mounted LEDs are the same as ordinary LEDs but small rectangular block shape (like a tiny LEGO brick) with solder pads at each end. I think simply placing the LED over two adjacent pads as you have put on your tester will make contact - simples! If you've not already done so, mark the tester pads + and - so you know which way round the LED will go before soldering. Cheers.

    Yeah, I'm going to label the terminals by sticking on some tape and marking it + and - , or A and K. I was also thinking about sticking or etching an LED quick-reference thing to the bottom of the tin.

    I usually do this type of work away from my computer because of the soldering that's involved most of the time.

    You have put groups of LEDS in parallel off one resistor but if you plug a red LED along with other colours you may find the coloured ones might not work as the red LED only needs 1.8v to operate and other colours are higher voltage. It would be better if each LED socket/plate had its own resistor. The higher value resistor should also be wired back to the battery or switch not in series like your schematic. Otherwise a neat test solution - I was thinking your plates may also allow surface-mounted LEDs to be tested easily. Good instructable - keep them coming

    1 reply

    Thanks for your feedback, theboffin. Yes, I know that LEDs should have their own resistors. However I felt for my purposes this should work well enough, and I usually will only test one at a time.
    I put that resistor in series with the 100 Ohm resistor to add some more resistance, and also to minimize the wires going to the batteries. The resistance is still low enough even for 3V LEDs. At first I had used 10k Ohms, but in combination with 100 Ohms the glow from any LED was too dim (in the photos I was still using 10k Ohms -- I fixed it after I took them).
    I've never used surface-mounted LEDs before. Do they need 3V like the regular 5mm LEDs?

    Very well done! A very good use of the old Altoids tin as well! Perhaps in place of the 3.3k resistor, you could use a 2.5k potentiometer with a 1k resistor in series with it in order to adjust the current flowing through those contacts. This would also allow you to check the current flow through an LED at any desired brightness by increasing/decreasing the variable resistance. You could then use the resistance value in other LED projects and have your LED at the "perfect" brightness.

    1 reply

    I like that idea. It would be a much simpler and more professional way to do it. Before I made this I was actually thinking about making a tester with higher currents, maybe with 9 or 12V, and a potentiometer. But I didn't have any useful potentiometers around (only some 5 and 10k) so I've "shelved" that idea to consider later.

    hey I have one of these too, its called a 3V battery. jk jk! this is actually really groovy. Love the design of it.