GPIO Pins

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.

The GPIO pins allow the Raspberry Pi to control and monitor the outside world by being connected to electronic circuits. The Pi is able to control LEDs, turning them on or off, run motors, and many other things. It’s also able to detect whether a switch has been pressed, the temperature, and the light. We refer to this as physical computing.

There are 40 pins on the Raspberry Pi (26 pins on early models), and they provide various different functions.

Raspberry Pi 1 Models A+ and B+, Pi 2 Model B, Pi 3 Models  A+, B and B+, Pi 4, and Pi Zero, Zero W, and Zero WH GPIO J8 have a 40-pin pinout. Raspberry Pi 1 Models A and B have only the first 26 pins.

In the Pi Zero and Zero W, the 40 GPIO pins are unpopulated, having the through-holes exposed for soldering instead. The Zero WH (Wireless + Header) has the header pins preinstalled.

GPIO 

A GPIO is a signal pin on an integrated circuit or board that can be used to perform digital input or output functions. By design, it has no predefined purpose and can be used by the hardware or software developer to perform the functions they choose. Typical applications include controlling LEDs, reading switches, and controlling various types of sensors. Most models of Raspberry Pi, for example, have a 40-pin GPIO connector that provides access to about 25 GPIO lines.

Voltages

Two 5V pins and two 3V3 pins are present on the board, as well as a number of ground pins (0V), which are unconfigurable. The remaining pins are all general-purpose 3V3 pins, meaning outputs are set to 3V3 and inputs are 3V3-tolerant.

The most common functions of GPIO pins include:

  • Being configurable in software to be input or output
  • Being enabled or disabled
  • Setting the value of a digital output
  • Reading the value of a digital output
  • Generating an interrupt when the input changes the value

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)

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