Electrical Continuity Tester

As electrical circuits incorporate more components and become more complex, problems can become difficult to diagnose through visual inspection alone. A continuity tester provides a useful tool for identifying faults in a circuit.

When Edison constructed the Pearl Street power station in lower Manhattan in 1880 and developed the world’s first electrical network connecting homes and businesses, there were no electricians or electrical engineers. Edison soon discovered the need for electrical tools for his workers to prevent damage to the equipment. A continuity tester is a basic electrical tool.

Build Instructions

A commercial continuity tester can be purchased for about ten dollars.


Figure 15. A commercial continuity tester


The circuit that you created in the preceding project (LED, resistor, and battery) can be adapted for use as a continuity tester.  Test a circuit or an element of a circuit such as a test lead (consisting of a length of wire with an alligator clip on each end, as shown in the illustration below). Place one end of a probe connected to the LED onto one end of the test lead. Then place the other end of the LED circuit onto the other end of the test lead. If the test lead is in good working condition, the LED will light up when the circuit is completed.


Figure 16. Using a battery and a LED as a continuity tester


The point at which test leads are attached to the alligator clips can sometimes corrode or become detached. If this occurs, the circuit will not be completed and the circuit will not light up.


To convert the LED circuit for use as a continuity tester, the components must be housed in case of some kind. There are many ways to do this, limited only by your ingenuity. One of the simplest methods is to tape the components to a popsicle stick.


Figure 17. A “popsicle stick” continuity tester


Another approach is to roll cardstock into a cylinder to create a tube and mount the components in the tube created in this manner. Another method sometimes used is to remove the parts from the casing of a pen or marker that has a large plastic barrel and mount the components inside the barrel of the pen casing.


Figure 18. Using the casing of a pen to house the components of a continuity tester


Another, more advanced method is to create a 3D printed design that is custom-made to house the components of the pen.


Figure 19. CAD design (top) and 3D printed case bottom for a continuity tester

The design for a 3D printed housing for a continuity tester is available on the Make to Learn site.