GPIO Basics

Learn how to control the Raspberry Pi Pico’s GPIO pins using C to turn digital outputs on and off.

Now that you’ve written a program and sent it to your Raspberry Pi Pico, it’s time to interact with the real world using the Pico’s GPIO pins.

GPIO stands for General Purpose Input/Output — these are the physical pins on your Pico that can send or receive digital signals.

What You’ll Learn

• What GPIO pins are and how they work
• How to set up a pin for output
• How to turn an LED on and off using C

What You’ll Need

• Raspberry Pi Pico (or Pico W)
• Breadboard (optional)
• 1x LED
• 1x 330Ω resistor
• Jumper wires

⚠️ Be sure to connect the long leg (anode) of the LED to the GPIO pin, and the short leg (cathode) to GND through the resistor.

You can use the mnemonic - ‘long is live’ to remember that the long leg is positive (anode) and connects to the GPIO pin.

GPIO Pin Overview

The Raspberry Pi Pico has 26 usable GPIO pins (0–28, skipping 23–24).

Each pin can be configured as:

• Output: send a HIGH or LOW signal (3.3V or 0V)
• Input: read whether the pin is HIGH or LOW

Blinking a Pin (Without Delay for Now)

Here’s the simplest GPIO example — we’ll just turn a pin HIGH, wait a bit, then turn it LOW.

#include "pico/stdlib.h"

int main() {
    const uint LED_PIN = 15;
    gpio_init(LED_PIN);
    gpio_set_dir(LED_PIN, GPIO_OUT);

    while (true) {
        gpio_put(LED_PIN, 1);  // HIGH
        sleep_ms(1000);
        gpio_put(LED_PIN, 0);  // LOW
        sleep_ms(1000);
    }
}

Replace 15 with the GPIO pin number you connected your LED to.

What the Code Does

• gpio_init(pin) sets up the pin for use
• gpio_set_dir(pin, GPIO_OUT) makes the pin an output
• gpio_put(pin, value) sends a HIGH (1) or LOW (0) signal
• sleep_ms(ms) pauses the program for the given milliseconds

Try This

• Change the pin number and wire up a different GPIO
• Change the blink speed with shorter or longer sleep_ms() values
• Try using true and false instead of 1 and 0

Summary

You now know how to:

• Set up a GPIO pin as an output
• Control voltage levels from C
• Blink an LED using code!

In the next lesson, you’ll combine all of this into the classic blinking LED project using your own circuit.

Next up: Blinking an LED

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