First, let me state clearly that I am almost completely electronic-electrically illiterate. I made this not knowing anything whatsoever about electronics, electricity, or the theory of either. I read a great deal of information on the Internet, asked a couple of friends who knew more than I do. I reasoned that if the main component was designed from the beginning to convert 120v AC to 12v DC, then it ought to do the job. You agree that I am not responsible for any damages arising from building, use, or misuse of this LED tester.

This is Instructable is for a completely free LED light tester. After several searches, inquiries, and general poking around the net, I was unable to find something that might help test some LED lights I had. It was suggested by many that I buy something, but the frugal nerd in me scoffed at that idea, and that little tiny voice in my head said "you can make something that won't cost you anything!"

And so I did.

Step 1: Here Are All the Parts

If you are anything like me, somewhere in your garage or attic you have a box full of these power supply adapters. They all look like the ones in the picture, more or less, and they all have that barrel plug on the end. Mine was from a set of speakers that I had for an old computer, and I dug it out and untangled it from a box that had about 30 of those things in it. Now, given that I am not an electronics guy, know nothing about it, and wouldn't know a volt from an amp from a watt if any of them bit me on the behind, I can't advise you which specific one to use if you choose to build this. I can only tell you what I used, and that's that.

The power supply/adapter I used had this stuff cast into the side of the case.

HON - KWANG
PLUG IN CLASS 2 TRANSFORMER
MODEL O: D12 - 10 - 1000
P/N: 66-000-118-01
INPUT: 120V 60Hz 25W
OUTPUT: 12VDC 1000mA

I also used:

1 regular mini Alligator Clip

1 - 8" length of Copper Wire

1 - 6" length of 2"x4" wood

2 - Copper Nails I had lying around

And that's pretty much it. Everything I had was lying around in my garage, and I bought absolutely nothing. And if you're anything like me, you won't have to buy anything either. Hence, "Free LED Tester". Free if you have all this stuff lying around. Which I did. If you have to buy all this, well, it's going to cost you a little bit of money, but not much.

Step 2: Setup

First, cut the barrel plug off the end of the wire. Separate the wires about 6" or so, and strip about 1/4" of the insulation so you can test the wires to find out which is Pos and which is Neg.

I had no idea what to do with the Multimeter I had, so I decided to research the net and found several good articles on how to use one. It's a nifty device.

First, plug the power converter-adapter into a wall outlet, making sure that the two bare wires aren't touching each other.

As far as the multimeter goes, I plugged the black plug in the "COM" port, and the red one in the "V/mA" port, set the dial to 20v, touched the other ends of the probes to the wires, and presto! I got a reading of -16.14 when I touched the probes to the wires the first time. I switched the probes and got a reading of 16.14 again, this time with no (-) sign!

From the research I've read, this told me that the wire the red probe was touching was positive when the reading was positive, so that's how I figured it out! This tells me that the power converter is actually putting out 16.14 volts. Good so far.

Step 3: Assembly

Now that I know which wire is Pos and which is Neg, I marked my piece of wood accordingly, with a dab of red paint and the symbols "+ POS" and "- NEG" I set one of the copper nails about halfway into the wood, and went on to the next step. I stripped off about 1.5" of insulation from the positive wire.

I then took my copper wire, wound it around a nail, and made a coil. That will serve as a bushing to put the head of the other copper nail about 1/4" above the surface of the wood, and give me a good contact point.

As for the negative wire, I soldered it to one of the Alligator Clips I had lying around, and slid the little black plastic cover back over the connection.

Just a note here, I had no idea how to solder, and so I read up on the net as well. Found a few good videos on YT, and watched them. I practiced a bit on spare pieces of wire, and I think I'm not bad for a rank amateur.

After attaching the clip to the Neg wire, I tacked that wire into the wood to keep it in place. On second inspection, I would have moved it back about an inch or so, but it's fine right where it is in the picture.

Notice in the other picture where I'm soldering the Pos wire to the copper nail? See that little copper coil off to the right? That's the "spacer bushing" I made from the copper wire.

This step is very important. I slid the copper coil spacer onto the Neg wire, and let it slide down a few inches. Then, I looped the stripped end of the wire around the copper nail, tight up against the head of the nail, and soldered it down. Once it was in place. I took it out of my home-made "helping hand" device. I put the wire from the power supply right next to the nail, and slid the coil up onto it, covering the wire, and the nail, over the soldered section. It fit right up against the head, and the tail of the wire came out from under the coil.

I tapped the nail into the wood until the coil just barely made contact with the wood, tested it again with the Multimeter (note, I got a little bit less current flowing, as the reading on the meter is 16.07 now. But at least it works. Nice.)

Presto! It's finished!

Step 4: Testing and Operation

This is what the finished product looks like.

To use it, simply plug the other end into a standard wall outlet, and you're ready to go.

Clip the black Alligator Clip to the Negative wire of whatever LED thing you're going to test, and then touch the Positive wire to the bare nail head, and it should light up. If it doesn't, you've mixed something up.

Be sure to not leave the light on for more than a few seconds. After all, this is simply a tester to make sure the lights light up. Just touch the Positive to the bare nail or to the coil, and you should get light.

Here are three of the types of LED lights I tested with my new tester.

The first one is a little bitty 2" long section of that strip light, with Amber LEDs that I got from a company called "Prestige Illumination" Scott is a nice guy, and if you want any custom strips made up, he's the guy to do it. Great prices and excellent service.

The second one is a red strip I got from Pep Boys Auto Parts, and wow, that thing is bright. Lights right up.

The third one is an Amber 2" round trailer marker light from Ebay.

As you can see, they all light up nicely.

If you do decide to build this, please note that I cannot be held responsible for any damaged goods, persons, workshops, or anything else stemming from the use or misuse of this tester. If you start a fire, you started it, not me.

Thanks, and I look forward to your comments! [If they're nice ones. Nasty ones I'm going to delete.]