Simple LED Tester




Introduction: Simple LED Tester

All too often circuits are built and dead LEDs are unwittingly soldered into them. Only when the circuit is tested does the creator realize that the LED doesn't work. It is then impossible to tell if it is the LED or circuit that is faulty. To combat this issue we have created a simple LED tester to be able to test the LED before using it.


  1. (4) 4''x5'' pieces and (2) 5''x5'' pieces of foam board to form the box
  2. (1) 3''x4'' piece of foam board to form the circuit board
  3. (1) double pole double throw switch
  4. aluminum foil
  5. (6) 5'' wires stripped at either side
  6. (1) 9 volt battery
  7. (1) 1 k resistor
  8. (1) 10 k resistor
  9. copper conductive tape
  10. super glue
  11. multimeter for testing conductivity

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Step 1:

Cut 6 total pieces of foam board, 4 5''x4'' and 2 5''x5''

In one of the 5''x5'' pieces, cut a whole with the same circumference as the switch top and smaller holes above it to insert the LED

Step 2:

Using superglue, glue the 4 smaller pieces together as the sides and the piece with holes to the top. Make sure to leave the bottom off for now so that the inside of the box is accessible.

Step 3:

Line the two smaller holes with aluminum foil.

To do this, wrap aluminum foil around the tip of a pencil.

Apply superglue around the outside of the aluminum foil and insert the pencil with aluminum foil and superglue into the hole.

Once the superglue dries, pull the pencil out of the hole. The aluminum foil should remain.

Trim the foil down to the hole.

Step 4: Circuit Board

Using the conductive tape, create a circuit board on the 3''x4'' piece of foam. If the tape must be bent (as seen in the red circles) make sure to bend it while keeping it attached. If it is cut and simply laid on top of another piece, the glue will inhibit conductivity.

Once the tape is laid out, drill the smallest holes possible directly at the end of each piece of tape (the green dots)

Place either end of each resistor into the holes next to the tape as pictured. Once placed, proceed to solder them, making sure to connect the wire to the tape.

Step 5:

Then attach the wires to their respective places as pictured. The video shows both sides to make the visual more understandable. Use a multimeter to find which prongs of the switch correlate to each other and attach as pictured. (note: the yellow wires go together and the green ones go together)

Step 6:

Bring the two wires not attached to the switch (the red and blue one in our picture) and put each one throught the small holes from the inside.

Step 7:

After everything is attached, insert the LED into the two aluminum slots.

Flick the switch in one direction and make sure the LED lights up. If it does not, switch which legs of the LED are in which hole. At this point, the LED should light up. After this, label the holes with positive and negative.

After, test to see which side of the switch is high resistance vs low resistance. Which ever side makes the LED dimmer is the higher resistance. Label these with a pencil.


When testing LEDs, make sure to start off with the higher resistance.

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    2 Discussions


    4 years ago

    Great instructable! Though for people who are newer to electronics may want a basic schematic.


    4 years ago

    Thanks for sharing this project! This will come in handy for so many!