Building a Continuity Tester

In the first make activity, students construct a simple continuity tester consisting of a battery, an LED, and two insulated wires. Students learn how to solder electrical components together and can use this device to investigate the conductivity of different materials.

Steps: 7


  • Battery
  • Battery Holder
  • Battery Clip
  • Soldering Iron
  • Solder
  • LED
  • Insulated Wire
  • Wire Strippers

See Invention Kit Inventory for materials and sourcing information

Step 1

Your first step is to identify how the batteries attach to the battery holder. Connect the batteries in the correct orientation. Attach the battery clip to the battery holder. Finally, strip away part of the insulation on the ends of the battery clip so that enough wire is exposed to attach an alligator clip to. 

Step 2

Take your LED and touch each leg to either end of the battery holder’s terminals. Does it light up? If not, flip the LED around and touch the legs to the battery terminal again. It should light up now.

This is orientation is very important. LED’s have a positive (+) and negative (-) leg, the positive is the longer of the two legs. The positive leg of the LED should attach to the red wire of the battery clip. The negative leg of the LED should attach to the black wire of the battery clip.        

Step 3

Wrap the red wire from the battery clip to the positive leg of the LED. This will make soldering the two parts together easier. 

Step 4

Soldering is an important skill for engineering. It allows us to make a strong electrical connection between two parts. You will use one hand to feed the solder and the other hand to melt the solder and flow it around the two parts. Soldering is an easy skill that anyone can pick up. You’ll be able to make all sorts of electronic projects once you learn this skill.

Turn on the soldering iron and wait while it heats up. In one hand, hold the solder (silver wire) and in the other hold the iron. Do not touch the tip or shaft of the iron. It is hot and will burn you. You will touch the tip of the iron to the metal terminal of the battery holder, wait several seconds while it heats up, and then slowly push the solder towards the metal terminal.

You should see the solder melt, and flow around the LED leg and metal terminal. Remove the solder iron, and place it back into the holder. The result should have a cone shape, almost like a Hersey Kiss. Trim the excess wire of the LED leg with the wire cutters.

Step 5

You should have a working continuity tester! To test it out, touch the black wire of the battery clip to the negative leg of the LED. It should light up when you touch them together. This indicates that the materials are conducting electricity. 

Step 6

Here is a photo of what the final continuity tester should look like.