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Raspberry Pi GPIO Pins

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Raspberry Pi GPIO Pins

A powerful feature of the Raspberry Pi is the row of GPIO (general- purpose input/output) pins along the top edge of the board. A 40-pin GPIO header is found on all current Raspberry Pi boards (unpopulated on Pi Zero and Pi Zero W). Prior to the Pi 1 Model B+ (2014), boards comprised a shorter 26-pin header.

For our purposes the pins on the Pi3 (which we are using) are the same as on the Pi2, but for advanced uses there are some differences from the pinout here.

GPIO pins

Any of the GPIO pins can be designated (in software) as an input or output pin and used for a wide range of purposes.

GPIO layout

Note: the numbering of the GPIO pins is not in numerical order; GPIO pins 0 and 1 are present on the board (physical pins 27 and 28) but are reserved for advanced use (see below).

Voltages

Two 5V pins and two 3V3 pins are present on the board, as well as a number of ground pins (0V), which are not configurable. The remaining pins are all general purpose 3V3 pins, meaning outputs are set to 3V3 and inputs are 3V3-tolerant.

Outputs

A GPIO pin designated as an output pin can be set to high (3V3) or low (0V).

Inputs

A GPIO pin designated as an input pin can be read as high (3V3) or low (0V). This is made easier with the use of internal pull-up or pull-down resistors. Pins GPIO2 and GPIO3 have fixed pull-up resistors, but for other pins this can be configured in software.

More

As well as simple input and output devices, the GPIO pins can be used with a variety of alternative functions, some are available on all pins, others on specific pins.

  • PWM (pulse-width modulation)
    • Software PWM available on all pins
    • Hardware PWM available on GPIO12, GPIO13, GPIO18, GPIO19
  • SPI
    • SPI0: MOSI (GPIO10); MISO (GPIO9); SCLK (GPIO11); CE0 (GPIO8), CE1 (GPIO7)
    • SPI1: MOSI (GPIO20); MISO (GPIO19); SCLK (GPIO21); CE0 (GPIO18); CE1 (GPIO17); CE2 (GPIO16)
  • I2C
    • Data: (GPIO2); Clock (GPIO3)
    • EEPROM Data: (GPIO0); EEPROM Clock (GPIO1)
  • Serial
    • TX (GPIO14); RX (GPIO15)

GPIO pinout

It’s important to be aware of which pin is which. Some people use pin labels (like the RasPiO Portsplus PCB, or the printable Raspberry Leaf).

A handy reference can be accessed on the Raspberry Pi by opening a terminal window and running the command pinout. This tool is provided by the GPIO Zero Python library, which it is installed by default on the Raspbian desktop image, but not on Raspbian Lite.

For more details on the advanced capabilities of the GPIO pins see gadgetoid’s interactive pinout diagram.

Warning: while connecting up simple components to the GPIO pins is perfectly safe, it’s important to be careful how you wire things up. LEDs should have resistors to limit the current passing through them. Do not use 5V for 3V3 components. Do not connect motors directly to the GPIO pins, instead use an H-bridge circuit or a motor controller board.