A chopper circuit
In our last Project we mentioned that transformers can be used in DC circuits if the current is "interrupted." This is a circuit that does just that - only we say it ltchops" DC instead of interrupting it.
When you finish wiring this Project, press the Key, You'll hear a "beeping" sound and the Meter pointer will swing. Can you tell what's happening just by looking at the schematic?
Here's the scoop: when you press the Key, electricity flows through the Transformer and Relay. But when current flows through the Relay, it turns the circuit off. When this happens, the spring action of the Relay closes the contacts again, completing the circuit once more (and it repeats all over again).
The DC is "chopped" by the Relay, when you press the Key again, you repeat this action. As the DC is chopped, it sets up a moving magnetic field in one coil of the Transformer.
This moving magnetic field in turn causes electricity to flow in the Transformer coil connected to the Meter. This type of circuit can be used with DC circuits where transformers are used. It's not likely we would want to use it with AC circuits - do you know why? (No fair peeking at the answer,)