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RPi
Model
Number
of GPIO
pins
Number of
inputs or
outputs
A
26
17
B
26
17
A+
40
28
B+
40
28
Pins 27-40 not available on older RPi models
Pin 1
Pin 40
Pin 2
Raspberry Pi Python GPIO Quick start guide
The GPIO pins on a Raspberry Pi allow you to connect your Pi up to all sorts of electronic devices. This guide talks you
through how to set up and control the inputs and outputs using python.
GPIO stands for General Purpose Input and Output.
GPIO pins are the metal spikes that stick out of a RPi.
Older RPis have 26 pins and newer ones have 40 pins.
Some of those pins are for power rather than inputs or
outputs
Pins:
Pins are either power points or I/O pins
Power pins are hard wired to 0v (ground), +3.3v or +5v. You can’t change them.
I/O pins can be set to either an input or an output
Inputs read a digital value into the RPi (e.g. has a switch been pressed?)
Output send a digital value out from the RPI (e.g. switch an LED on or off)
Pin numbering:
There are two numbering systems for GPIO pins.
Physical numbering is the easiest to understand: it tells you where to find the pin on the physical RPi board
(see below)
BCM numbers are only for I/O pins. They don’t match the physical numbers but come from the way that
they are connected to the processor on the RPi.
When writing your code you can choose to use either physical numbering or BCM numbering
Warning:
You might permanently break your RPi if you’re not careful when connecting anything to the GPIO pins.
Short circuits (connecting +3v or +5 either from a power pin or an output pin directly to ground) will
damage your RPi
Whilst your GPIO pins have power pins, there’s a limit to how much power they can provide. You may need
an external power supply if you’re controlling a circuit that needs anything more than a few LEDs &
switches.
Never connect a motor or speaker directly to a GPIO pin. The electrical feedback can cause damage.
Controlling the GPIO in python
You can simulate and test these commands without a RPi on create.withcode.uk
Import the GPIO module
You’ll need to do this once at the start of your code so
that you can use the GPIO module to access the inputs
and outputs.
Setup inputs and outputs
All I/O pins are set to be inputs unless you write code to make them outputs.
This example sets the RPi to use physical pin
numbering then sets physical pin 3 to be an output.
Change GPIO.BOARD to GPIO.BCM if you want BCM pin numbering instead of physical pin numbering
Change GPIO.OUT to GPIO.IN if you want to set a pin back to being an input
Reading inputs and setting outputs
The time module is useful for adding delays to
pause your program
We’ve set up physical pin 3 (BCM2) as an
output and physical pin 5 (BCM 3) as an input:
GPIO.output sends a value to an output pin
time.sleep(1) pauses the program for 1
second
GPIO.input reads a value from an input pin
You can run this code online with a simulated Raspberry Pi here;
https://create.withcode.uk/python/A3
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