STM32: RGB LED Color Cycle is a runnable microcontroller simulation example on SensBench — open the wired circuit, inspect the code, and compile real firmware in your browser, no install needed. Last updated Aug 14, 2026.

FREE SIMULATOR EXAMPLE · BEGINNER

STM32: RGB LED Color Cycle

This example cycles an RGB LED through six colors — red, green, blue, yellow, cyan, magenta — using three GPIO pins (PA0=R, PA1=G, PA2=B) on the STM32 Blue Pill. Each color is a pure digital combination, printed to the Serial Monitor as it shows.

▶ Open in the Simulator Get the parts

Board	STM32 Blue Pill (STM32F103C8, Cortex-M3, 72 MHz)
Difficulty	beginner
Category	basics
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

STM32 Blue Pill cycling an RGB LED through red, green and blue on PA0-PA2 in the Sensbench simulator

The exact circuit you get when you open this example — already wired, ready to run.

The sketch

// STM32 Blue Pill (F103) — RGB LED color cycle
// R=PA0, G=PA1, B=PA2, common cathode (COM -> GND).
const int PIN_R = PA0, PIN_G = PA1, PIN_B = PA2;

void setup() {
  Serial.begin(115200);
  pinMode(PIN_R, OUTPUT); pinMode(PIN_G, OUTPUT); pinMode(PIN_B, OUTPUT);
}

void show(bool r, bool g, bool b, const char* name) {
  digitalWrite(PIN_R, r); digitalWrite(PIN_G, g); digitalWrite(PIN_B, b);
  Serial.println(name);
  delay(700);
}

void loop() {
  show(true,  false, false, "RED");
  show(false, true,  false, "GREEN");
  show(false, false, true,  "BLUE");
  show(true,  true,  false, "YELLOW");
  show(false, true,  true,  "CYAN");
  show(true,  false, true,  "MAGENTA");
}

How it works

Three pins — PA0 for red, PA1 for green, PA2 for blue — are set as outputs, and a show() helper takes three booleans and a name. Each call writes all three pins, prints the color name to Serial, and holds for 700 ms. The loop walks through red, green, blue, yellow, cyan, magenta — every combination except all-off.

The show() helper keeps the main loop declarative: one line per color instead of six digitalWrite() calls repeated per step. The serial print doubles as a debugging aid — the monitor tells you which color should be on the canvas, so a wiring error is easy to spot.

Before you build it for real

The simulator places the LED with no current-limiting resistors, which a real build absolutely needs: each channel wants its own series resistor (typically 220 Ohm for red, 150 Ohm for green and blue) or the F103’s pins will exceed their current limits and eventually fail. The LED’s forward voltage also differs per color — red is about 2 V, green and blue about 3 V — so at 3.3 V logic, green and blue will look dimmer unless you pick resistor values per channel. A common-cathode LED needs COM to GND; wiring COM to 3.3 V shorts all three channels.

Get the parts

Solderless Breadboard 830-Point In the simulator it is free — this is for your real bench.Jumper Wires M-M 40pcs In the simulator it is free — this is for your real bench.

Related examples

STM32 Blue Pill BlinkRun in simulator →STM32 Blue Pill 7-SegmentRun in simulator →Arduino Uno RGB CycleRun in simulator →

FAQ

Why only six colors instead of a full rainbow?

Each pin is a digital output — fully on or off — so the three channels give 2^3 = 8 combinations, one of which is all-off. For smooth gradients and mixed hues you need PWM on the pins, which the F103’s timers support; this example is deliberately pure digital to teach the GPIO basics first.

What does common-cathode mean and why does it matter?

Common-cathode means all three LED cathodes share one pin (COM), which goes to GND, and the anodes are driven HIGH to light. If you buy a common-anode RGB LED instead, the logic inverts and driving a pin HIGH turns the color OFF — you would need to flip every true to false.