GPIO

Pick up a Raspberry Pi Pico or an ESP32 and you will find a row of little numbered pins around the edge. Those are GPIO pins — and they are the reason your code can make things happen in the physical world.

What is GPIO?

GPIO stands for General-Purpose Input/Output. Each pin on a microcontroller or single-board computer can be set up, in software, to either read a signal coming in (input) or send a signal going out (output).

In output mode a pin can switch an LED on and off, drive a buzzer, or tell a motor driver to spin a wheel. In input mode the same pin can detect a button press, read a switch, or receive a signal from a sensor.

Pins are digital by default — they deal in two states: HIGH (usually 3.3 V) and LOW (0 V). Many boards also have pins that can read analogue voltages using an analogue-to-digital converter (ADC), which turns a smoothly varying voltage into a number your code can work with.

Input and output

The same pin can do two opposite jobs depending on how your code configures it. As an output it pushes voltage out to drive something; as an input it reads voltage coming in. Here are the two everyday wiring patterns — an LED on an output and a button on an input:

   OUTPUT — drive an LED            INPUT — read a button

   GPIO ──[220Ω]──▶|── GND          3.3V ──[10kΩ]──┬── GPIO
                   LED                              │
                                                  [BTN]
   pin HIGH → LED on                                │
   pin LOW  → LED off                              GND

                                    not pressed → reads HIGH
                                    pressed     → reads LOW

The 10 kΩ resistor on the button is a pull-up: it holds the pin at a known HIGH until the button connects it to ground. Without it the pin “floats” and reads random noise — a classic beginner gotcha.

Why robot builders care

GPIO is the connection point between your software and everything physical. Without it, a robot is just a piece of code sitting idle.

• Sensors — ultrasonic rangefinders, infrared sensors, and temperature modules all talk to your microcontroller through GPIO pins.
• Actuators — motor drivers, servos, and LEDs all take their orders from GPIO signals.
• Feedback loops — reading a sensor on an input pin and reacting on an output pin is the foundation of every autonomous behaviour.
• Protocols built on GPIO — I2C, SPI, and UART are all implemented on top of dedicated GPIO lines. Understanding plain GPIO first makes those protocols far less mysterious.

Get started

The classic first GPIO project is a blinking LED — an output pin switches an LED on and off in a loop. From there, add a button on an input pin and you have got user interaction. It sounds simple, but this two-pin circuit is the kernel of a robot’s control loop.

The Raspberry Pi Pico with MicroPython — GPIO Mastery course covers everything from pin modes and pull-up resistors to reading analogue sensors and driving outputs. It is the most direct path from “what is a GPIO pin?” to confidently wiring up real hardware.

When you are ready for a practical project, the Hacky Temperature and Humidity Sensor is a great low-cost build that reads a DHT22 sensor through a single GPIO pin on a Pico. It proves the point quickly — a few lines of MicroPython, one pin, and you are logging real environmental data.

If you want to explore more input types, the Reed Switches post shows how magnetic switches wire into GPIO input pins.

One practical tip: always check your microcontroller’s pin voltage. Most GPIO pins operate at 3.3 V. Connecting a 5 V sensor directly can damage the pin permanently — use a voltage divider or a level shifter.