Candle

Real candles never sit perfectly still. Their flame breathes, dances and flickers unpredictably. That is exactly what makes them feel alive — and what we can approximate with a single LED and a little randomness in software.

In this project we turn one LED into a candle flame by rapidly varying its brightness with software-controlled PWM. It is a lovely small effect and a perfect excuse to combine GPIO output with a pinch of chaos.

Source code: projects/candle/Candle.java

What You Will Learn

How to simulate PWM in software to control LED brightness
How to introduce randomness into an embedded program
How small timing changes affect the visual feel of a light
How to think about "organic" instead of "digital" effects

Components

Raspberry Pi
1 warm-white or yellow LED (orange also works well)
1 × 220Ω resistor
Breadboard
Jumper wires
Optional: a translucent cover (paper cup, tissue paper, wax paper) to diffuse the light

Wiring

Connect the anode (longer leg) of the LED to a GPIO pin through a 220Ω resistor.
Connect the cathode (shorter leg) to any GND pin.
Optionally place a small paper cup or a piece of tissue over the LED to diffuse it and get a more candle-like glow.

How It Works

Instead of turning the LED fully on or fully off, the program does software PWM: within every short cycle, it turns the LED on for a fraction of the time proportional to the desired brightness. By quickly changing that fraction with a random component, the LED looks like it is flickering.

The recipe is:

Pick a target brightness between "dim ember" and "bright flame".
For a short interval, PWM the LED at that brightness.
Randomly nudge the target brightness a little bit.
Repeat forever (or until you power off).

Possible Enhancements

Combine several LEDs of slightly different colors for a richer flame
Add a microphone and let the "candle" react to sound (blow it out)
Add a physical button to "light" and "extinguish" the candle
Use a proper hardware PWM pin for smoother control
Group many candles together for a virtual altar or tea light set

Why It Matters

Digital electronics are, by default, very square: on or off, high or low. Making things feel natural — like a flickering flame, a breathing heartbeat or a gentle wave — requires layering timing, brightness and randomness. This tiny candle is a great first step in that art.