Signals and controls
Indicator LED
A small indicator that makes program state visible.
What it does
An LED conducts mainly in one direction and emits light when forward current flows. A resistor limits that current.
Connections and compatibility
For the Uno exercises, connect the output through a 1 kΩ resistor to the anode, and the cathode to ground. Check package markings if the leads have been trimmed.
Choosing one
Any ordinary low-current indicator LED is suitable. Use the board’s built-in LED when no external indication is needed.
Common mistakes
An LED is not a resistor. Connecting it directly across a supply can damage it or the output pin.
Use it in a tutorial
- Analog and PWM signals — Use a potentiometer to control an indicator, and learn how analog measurements differ from PWM outputs.
- Blinking an LED — Wire a low-current status indicator and blink it without blocking the rest of your program.
- Shift registers — Use a 74HC595 to drive eight low-current indicators with three controller pins.
- Transistors — Build a low-side transistor switch, then learn what changes when the load becomes a motor or relay.