Building a Switch-Controlled Circuit

Adding a simple mechanical switch to break and complete a circuit's current path on demand.

You'll need: your LED circuit from Lesson cb-02, plus a single-pole switch or push-button, and a multimeter set to continuity mode (Lesson 16) to test it first.

A switch is nothing more than a controllable break in the wire: open, no current can flow anywhere in that loop, so nothing downstream works no matter how correctly it's wired; closed, it behaves exactly like a plain wire, and current flows as if the switch weren't there at all.

Before wiring a switch into a live circuit, test it in isolation: set your multimeter to continuity mode, touch a probe to each terminal, and confirm you hear the beep only when the switch is closed (or, for a push-button, only while pressed). This catches a wired-wrong or faulty switch before it becomes a confusing "my circuit doesn't work" mystery.

Placement matters only a little: a switch works the same wired on the positive side or the ground side of the loop, as long as it sits somewhere in that single series path. Add it between your battery and the resistor from Lesson cb-02, and you have a circuit you can turn on and off on demand.