If you’re like me, you probably like to save and collect those LED lights from your old electronic equipment before you toss it out. But how do you know what type of LED it is? How do you know what color the LED is? How do you know if it works? You can create a small unit to test LED’s with some parts that are probably lying around in your house. Here’s what you need…

  • 1 battery case that holds two AAA Batteries (Radio Shack No. 270-414)
  • 1 resistor (Suggested: 39 Ohms – Orange, White, Black, Gold)
  • 1 two pin female connector plug (a plug from a computer fan works well)
  • Heat shrink tubing

You will also need wire strippers and electrical tape. You probably might want to use a soldering iron to solder the wires onto the resistor. I just twisted the wires on the resistor as the heat shrink tubing will help hold the wires in place.

The battery case will hold two AAA batteries totaling to 3 volts. Because fresh batteries may contain a little extra voltage, you will need to use a resistor to protect the LED’s from damage and failure. I recommend a 39 ohm resistor with an orange, white, black, and gold stripe in that order. This will step the voltage down to roughly 2.8 volts and will help maintain the brightness. You may use a resistor of a different ohm value, but the LED brightness may be dim.

The connector on the other end makes it easy to insert and remove a LED. The connector will hold the LED in place and will not fall out.

  1. Slide some heat shrink over the wires on the battery case, enough to cover the resistor when you are done making connections.
  2. Connect the positive lead from the battery case to one end of the resistor.
  3. Connect one of the two wires of the connector plug to the other end of the resistor.
  4. Connect the other wire of the connector plug to the negative wire on the battery case. Use some electrical tape to cover the bare negative wires.
  5. Slide the heat shrink over the resistor and the joined negative wires. Before heating the heat shrink, install the batteries and make sure the circuit works. If the LED doesn’t light, remove the LED and turn it around. Because a LED is a diode, it will only work one way. If the circuit works, remove the LED and batteries and heat the heat shrink.

There you have it! A portable LED tester that’s small and convenient.