Use the Raspberry Pi I2C Interface to Connect to a Device

This example shows how to create a connection to an I2C device, write data to the device, and read data from the device.

Warning

Excessive voltage and current can damage the Raspberry Pi™ hardware. Observe the manufacturer’s precautions for handling the Raspberry Pi hardware and connecting it to other devices. For more information, see https://www.raspberrypi.org/technical-help-and-resource-documents.

Create a connection to the Raspberry Pi hardware using raspi.

mypi = raspi
mypi = 

  raspi with properties:

           DeviceAddress: 'raspberrypi-computername'
                    Port: 18725
               BoardName: 'Raspberry
        Pi Model B Rev 2'
           AvailableLEDs: {'led0'}
    AvailableDigitalPins: [4 7 8 9 10 11 14 15 17 18 22 23 24 25 27 30 31]
    AvailableSPIChannels: {}
      AvailableI2CBuses: {'i2c-0'  'i2c-1'}
             I2CBusSpeed: 100000

  Supported peripherals

The default I2C bus speed is 100000 bits per second.

You can redisplay the AvailableI2CBuses and I2CBusSpeed properties.

mypi.AvailableI2CBuses
mypi.I2CBusSpeed      
ans = 

    'i2c-0'    'i2c-1'


ans =

      100000

Show the location of the I2C pins on the GPIO header.

showPins(mypi)

The pin map shows that, for this model and revision of the board, the i2c-1 bus is available on the GPIO header pins I2C1_SDA (GPIO 2) and I2C1_SCL (GPIO 3).

Raspberry Pi hardware uses +3.3V. Do not connect Raspberry Pi hardware directly to devices that deliver higher voltages.

Before continuing, research the manufacturer’s product information to determine which settings the I2C device supports. Then, connect the Raspberry Pi board to the I2C device.

For example, with the MCP4725 12-bit DAC, connect:

  • I2C1_SDA (GPIO2) pin on the Raspberry Pi board to the SDA pin on the DAC.

  • I2C1_SCL (GPIO3) pin on the Raspberry Pi board to the SCL pin on the DAC.

  • GND on the Raspberry Pi board to the GND pin on the DAC.

  • +3.3V on the Raspberry Pi board to the VDD pin on the DAC.

  • VOUT pin on the DAC to the positive lead on the voltmeter.

  • GND to the negative lead on the voltmeter.

Get the addresses of I2C devices that are attached to the I2C bus, 'i2c-1'.

scanI2CBus(mypi,'i2c-1')
ans = 

    '0x62'

Create a connection to the I2C DAC at '0x62' and assign that connection to a handle, i2cdac.

i2cdac = i2cdev(mypi,'i2c-1','0x62')
i2cdac = 

  i2cdev with properties:

        Bus: 'i2c-1'
    Address: '0x62'

Write a value to the I2C device.

write(i2cdac,4092)

To read a value from an I2C sensor, physically connect the sensor, use scanI2CBus to get the address, use i2cdev to create a connection to the device. Then, use read to get the value.

addr = scanI2CBus(mypi,'i2c-1')
i2csensor = i2cdev(mypi,'i2c-1',char(addr))
read(i2csensor,1)

If you are not using I2C, disable I2C to make additional GPIO pins available.

Note

Before disabling I2C, clear the i2cdev object, if created. For example, clear (i2csensor).

disableI2C(mypi)

When you use I2C again, enable I2C.

enableI2C(mypi)

To change the I2C bus speed, mypi.I2CBusSpeed, use enableI2C with the i2cBusSpeed argument.

disableI2C(mypi)
enableI2C(mypi,400000)
mypi.I2CBusSpeed
ans =

       40000