The latest addition to our collection of beginner projects, some useful, some instructive and some amusing, which can be made for around the ten UK pounds mark.

When you switch on a newly built project and it fails to work, the reason is often an "open circuit" (where a desired connection has not been made), a "short circuit" (where an unwanted connection has been made), or maybe a few of both.

There are a number of devices available for checking circuits. Often a multimeter includes the facility for testing short-circuits (sometimes referred to as "continuity testing").

The Circuit Tester in this project is a simplified version of the very precise resistance-measuring circuit known as a "Wheatstone Bridge".