Building a Status Indicator Circuit

Two LEDs, wired to show mutually exclusive states — a simple, readable way to display 'on/off,' 'charging/full,' or any two-state status.

You'll need: two LEDs of different colors (red and green work well), two current-limiting resistors, and a way to toggle between two states (a switch, or later, a transistor driven by another part of your circuit).

Rather than one LED that's either lit or dark, a two-color status indicator makes the current state unambiguous at a glance: red clearly means one thing, green clearly means another, with no dark/off state to misread as "broken" versus "off."

The simplest version wires each LED (with its own resistor, following Lesson cb-04's parallel-branch rule) to opposite positions of a single-pole double-throw switch, so exactly one LED is ever lit at a time — switch one way for red, the other for green, never both, never neither.

A more automatic version replaces the manual switch with a transistor (Lesson cb-10): the transistor's "on" state lights one LED directly from the supply, while its "off" state — using a second resistor path — keeps the other LED lit instead, so the pair automatically shows whichever state your control signal represents, no manual flipping required.