Raspberry PI Multiple I2C Devices

4 years ago

source link: https://www.instructables.com/Raspberry-PI-Multiple-I2c-Devices/
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Step 2: Case One: I2c Devices Have the Same Address

This was always the problematic case. An i2c bus can handle multiple devices, but they should have different i2c addresses. Some i2c devices have jumpers to set other i2c addresses, but many don't. In this case you may use a i2c multiplexer (hardware) to rotate the i2c SDA (Data) and SCL (Clock) or you can create an additional i2c bus or more.

I will create two aditional busses, nl bus 3 and 4

Open the cli and run

cd /boot

sudo nano config.txt

Add the following line of code, preferable in the section where spi and i2c is enabled.

dtoverlay=i2c-gpio,bus=4,i2c_gpio_delay_us=1,i2c_gpio_sda=23,i2c_gpio_scl=24

This line will create an aditional i2c bus (bus 4) on GPIO 23 as SDA and GPIO 24 as SCL (GPIO 23 and 24 is defaults)

Also add the following line to create i2c bus 3

dtoverlay=i2c-gpio,bus=3,i2c_gpio_delay_us=1,i2c_gpio_sda=17,i2c_gpio_scl=27

GPIO 17 will be the SDA and GPIO 27 will be the SCL for i2c bus 4.

Tipe control X to exit.

Note on the Bus Numbering and order:

Never use bus 0 and 2, it is use for other things in the board like eprom on hats etc

For the April 2019 raspbian release:

You should always start with the highest bus (Bus 4 in this case) in your config.txt and work through to the lowest bus (bus 3).

The lowest bus must always be bus 3

If you need 5 extra busses, the busses must bi in the order of 7,6, 5, 4, 3

This issue on bus order was not there when this Instructable was originally written. It seems like changes was made to the kernel.

Shut down your PI, switch it of. Connect your i2c devices to bus 4 (SDA to GPIO 23 and SCL to GPIO 24) and the other to i2c bus 3 (SDA to GPIO 17 and SCL to GPIO 27).

Switch on the pi.

sudo i2cdetect -l (Lower Case L)

You will now see that i2c bus 3 and 4 is also listed. Also run:

sudo i2cdetect -y 3

sudo i2cdetect -y 4

Now you can use your sensor in your programming language. Remember to specify the correct i2c busses.

Attach is an example for the popular BMP280 Temperature and Pressure sensor. No multiplexer can read 2 BMP280s this fast.

An example of 2 Sensirion SDP 810 sensors is also attach. Again working much faster than the multiplexer I used in the past

I created python code to read two new BMP388s from adafruit.

I may also add other sensors in future to https://github.com/JJSlabbert/Raspberry_PI_i2C_conficts

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