Here is a very simple experimental setup for those who are learning electricity or electronics or as a subject for science education. The circuit can test small, medium and large cells. It is a simple electromagnetic indicator made entirely of alternative material: a nail, a piece of wood and a piece of preserved can.
The coil, wrapped around the nail, is formed by 200 to 500 turns of very fine enameled wire that can be harnessed from old transformers or coils.
The nail is 2 to 3 cm long is fixed on a tablet with a can that will be spaced about 2 mm as shown. When we clamp the terminals of a stack, the circulating current magnetizes the nail which then attracts the canister producing an audible click.
Failure to do so is because the battery is exhausted or very weak. If the movement of the can is small, it is because the battery is weakened. Remember to scrape the enameled wire in the place that makes contact for the probe.
