It should take about 10 minutes to build with parts most any hobbyist probably has lying around. This thing has saved me countless headaches from removing and replacing faulty LEDs in large arrays!
Step 1: Proof of Necessity
I buy cheap LEDs. It's no secret, and I'm not ashamed of it. The 10¢ difference between a 10¢ and 20¢ LED from two different distributors can really add up when you buy a few hundred at a time. Even if 10% of the cheaper LEDs are faulty, there is still a savings of 45%. The caveat is that each LED needs to be tested before it is used to ensure it actually works. Otherwise, you may be spending a lot of time disassembling something just to replace a couple of LEDs that don't work - this is no easy task in a large array of LEDs that have been soldered together and sealed in some enclosure. It is much less time consuming and frustrating to just test them all first.
Step 2: Gathering Materials
Battery - The best option here is a single 9V battery - alkaline or rechargeable, but anything (or any string) producing at least 4V should work OK for most LEDs.
Battery Holder / Connector - Whatever will work to connect your battery to the circuit.
2 x Resistors - I use 1000 ohm through hole resistors for this project. For an LED forward voltage of 3V with a 9V battery, there should be 6V left - 3V across each resistor. That means 3mA [ 3V / 1000ohms ] should flow through the LED - plenty enough to see if it is working. If you want more current for a brighter LED or you are using a lower voltage battery, use smaller resistors.
Cardboard - This forms the body of the device. I used a 1" x 8" strip.
Scissors - To cut the cardboard.
Electric Tape - To hold the cardboard together.
Hot Glue with gun - To secure the resistors in place.
Soldering Iron and Solder - To resistors to the battery cable.
Heat Shrink and Heat Gun - Not entirely necessary, but protects the solder joints.
Step 3: The Build
- Cut the cardboard into a long strip and fold in half. The ends can be folded up again for more support at the base.
- Wrap the cardboard with electric tape to hold it together.
- Solder one end of one resistor to the positive battery cable.
- Solder one end of the other resistor to the negative battery cable.
- (Optional) Shrink heat tubing over the solder joints.
- Fold the unsoldered lead of one resistor into a 'U" and glue it down with a section of exposed lead running along the top of the cardboard.
- Repeat step 6 with the other resistor on the other side of the cardboard.
- Connect the battery, and test an LED by inserting the top of the tester in between the LED leads, minding the polarity of the battery and LEDs.