Source: GPIOs Inputs and Outputs

Overview

The Raspberry Pi (and reTerminal) expose 40 GPIO pins that can be configured as input or output in software.

2× 5 V pins, 2× 3.3 V pins, multiple GND pins (not configurable)
All remaining GPIO pins: 3.3 V logic (outputs set to 3.3 V, inputs are 3.3 V-tolerant)

Run pinout in terminal to see the GPIO reference map (provided by GPIO Zero).

Outputs

Set high (3.3 V) or low (0 V)

Inputs

Read as high (3.3 V) or low (0 V)

No Native Analog (ADC)

The Raspberry Pi does NOT have a built-in ADC.

To read analog signals, use an external ADC — in this course: Grove Base Hat for Raspberry Pi.

Grove Base Hat

4 analog (ADC) connectors — each with 12-bit resolution (0–4095)
Also exposes: 6 digital, 3 I2C, 1 PWM, 1 UART connectors
Adds-on (HAT) to the Raspberry Pi 40-pin header

Digital Communication Protocols on GPIO

Available on GPIO pins (some on all pins, some on specific pins):

Protocol	Type	Notes
PWM	Digital (simulated analog)	Pulse-width modulation
SPI	Synchronous serial	Controller/peripheral, separate clock
I2C	Synchronous serial	2 wires, multiple devices
Serial (UART)	Asynchronous serial	TX/RX, point-to-point
PCM	Pulse-code modulation	Audio

Permissions

User must be in the gpio group to use GPIO:

sudo usermod -a -G gpio <username>

(default user is already in the group)

GPIO Zero Python Library

from gpiozero import LED, Button, PWMLED, Servo
from time import sleep

LED (GPIO 17)

led = LED(17)
led.on()
led.off()
led.toggle()
led.blink()   # blinks indefinitely

Button (GPIO 2)

button = Button(2)
if button.is_pressed:
    print("Pressed")
 
# Callbacks
button.when_pressed = led.on
button.when_released = led.off
 
# Blocking
button.wait_for_press()
button.wait_for_release()

Button + LED combined

from gpiozero import LED, Button
led = LED(17)
button = Button(2)
while True:
    if button.is_pressed:
        led.on()
    else:
        led.off()

co-test

Explorer

gpios-inputs-and-outputs