Here is a little back story for this quick and very useful project. I am in the process of designing and building a small indoor green house, which will have LED based grow lights in it. I bought a couple of LED grow light boards from homegrownlights.com, so I needed to install 256 LEDs per board and having a total of 10 boards to populate with some 2,560 LEDs, I wanted a way of testing the LEDs before I went through the process of soldering them in. I had a couple requirements as I went into building my tester. First it had to be easy to use. Second it had to be simply and compact once built. Third it had to be cheap, but would last a while for other LED projects. So here is my design, it's quick, clean, and easy to use. I was able to test 2,000 LEDs in about an hour and 15 minutes.

Step 1: Parts + Tools

Parts:
- Small project box (3"x2"x1")
- A piece of 2-sided copper clad PC board (2"x2")
- CR2032 Button Battery holder
- CR2032 Button Battery
- Small peice of wire (not in picture)

Optional potentimeter to be able to turn voltage down for LEDs that require lower voltages. I built it to test 3-4VDC LEDs, so running just a 3VDC button battery worked for me, but I am going to add the adjustability later.

(I bought everything at Radio Shack. I'm lucky enough to live in a college town with a large engineering school, so the Radio Shack actually still carries components.)

Step 2: Cut PC Board to Size

Ok if you got your project box from Radio Shack then this step is going to be a piece of cake and it's no lie. If you did get the box from Radio Shack then you can use the picture below as a templet. If you didn't then you can use the templet as a guide as to what shape you will want it and use your own dimensions.
To cut the PCB I used a rotary tool and a utility knife. I used the utility knife the trace along the cut lines as to not have any chip out from the rotary tool. (Which I still had, but it's ok, function not form)

Step 3: Drill the Holes

Mark the PCB for the holes for the battery holder. The placement for the battery holder should be with the lower edge lining up with the lower edge of the PCB, this should be pretty much perfect for the battery holder to fit inside the box with the cover on. I installed the battery holder with the positive side on the right, so that will be where you will drill your third hole for the short piece of wire.
Choose a drill bit that is just big enough for the battery holders leads to fit through them. With this bit drill the three holes for the battery holder and short piece of wire.

Step 4: Grind the Circuit Into the Board

This step could be done with etching, but way go through all that trouble when two quick lines with the rotary tool can have it done just as well and quicker. You just need to get through the layer of copper cladding. Do need grind all the way throught the board just the layer of copper.
Grind the two lines into the copper cladding according to the pictures below. The two sides should look the same when it comes to the gaps that you will create by grinding the lines through the copper.

Step 5: Solder the Circuit

This is the easy part. Solder the battery holder onto the PCB on the positive side.

You will have to connect the two sides of the PCB using the short piece of wire through the third hole that you drilled next to the positice hole. This will get the positive onto the other side of the board.

Step 6: Cut the Slot in the Cover

Now you need to cut a slot in the cover for the testing end to stick through. To do this take the tester board and slide it into the box. Now you can take the cover and lean it against the tester with one side edge against the box and mark the cover with a pen or make a scratch with the knife. Now do the same thing but with the far end edge against the box. Now you should have a pretty good idea where the slot needs to go, just make sure that you make the slot wide enough.
I made the slot by drill a series of holes in a straight line where I determined the slot needed to be. Take the knife and smooth out the hole and test fit the cover over the tester.
Once you are happy with the fit, you can put the battery in and install the tester and screw the cover on.

Step 7: Test the Tester

Before I used it to test a LED, I tested the Tester with a multimeter, to make sure that I knew which side was which. It would be a good idea to mark the sides. I was getting 3.2VDC from the tester, so I was ready to test some LEDs.

Testing methods:
Small quantity method:
Take an LED and slide the leads on either side of the testing plate and pinch with tumb and index finger.

Large quantity method:
You will need three containers: One for the untested LEDs, one for the Good tested LEDs, and one for the Bad tested LEDs.
Once you have that all set up, you will need to sit down in a comfy chair (recliner if available), put in a movie or turn on some music.
And comence the testing frenzy. You fall right into a groove and breeze right through thousands of LEDs.

Results: LED lights up = Good LED
LED Doesn't light up = Bad LED or Reversed LED (Spin LED 180 degrees and test again if it still doesn't light = Bad LED)
LED Kinda lights up = Weak LED (Depending on what the LED is for this either good or bad, it's up to you)

Step 8: Final Thoughts and Future Revisions

This is a good little tester that will let you quickly test LEDs to weed out the dead ones or extremely weak. It also only works with through hole design LEDs with the current design, but I have ideas and plans on adding the ability to test surface mount LEDs and maybe even multicolor LEDs.

If you need to test LEDs that require less than 3VDC then I would recommend adding a resister into the circuit or do what I plan on doing for a future modification and add a potetimeter.

Make sure you don't just throw it into you tool box as there is no power switch and always has power going to the test plate. A cover for the Test plate would be a good idea.

I would love to hear about and see any ideas or improvements you have for this little
tester.

And don't forget to vote for this instructable.