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What is an I²C Bus on an ESP32 and ESP8266?

The I²C (Inter-Integrated Circuit) is a communication protocol used to connect different electronic components, like sensors and microcontrollers, on the same circuit board. It was invented by Philips Semiconductor (now NXP Semiconductors) and is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers. It's pronounced I-squared-C or I-two-C. Essentially, it enables easy and efficient communication between different parts of an electronic device.

How can you configure an I²C Bus on an ESP32 or ESP8266?

You can configure the I²C Bus quite easily using ESPHome for use with sensors. I'll spare you the technical details about this process, but you're more than welcome to have a look yourself at The I²C Bus in ESPHome.

Here's an example configuration you can use for your I²C Bus on a ESP32 device:

i2c:
  sda: 21
  scl: 22
  scan: true
  id: bus_a

And If you've got an ESP8266 device instead, you can use this configuration:

i2c:
  sda: 4
  scl: 5
  scan: true

You might notice the missing id in the configuration for the ESP8266. This field is optional because this device only supports 1 I²C Bus. The ESP32 supports 2 buses, so by using the id, you can differentiate between the two configured buses.

If you're not looking to change any of the default values in your configuration, you can also specify just specify the i2c block without any additional information:

i2c:

The default values will now be used. You can find the default values here: Default configuration values.

How do you use the I²C Bus with a sensor?

We've found out that the ESP32 supports 2 buses, so its configuration will look a little different than the ESP8266. Let's have a look:

i2c:
  - id: bus_a
    sda: 13
    scl: 16
    scan: true
  - id: bus_b
    sda: 14
    scl: 15
    scan: true

sensor:
- platform: bme680
  i2c_id: bus_b
  address: 0x76

This configuration shows 2 buses being configured for an ESP32, each sensor has its own unique id, so we can easily reference it in the sensor configuration. As you can see in the sensor configuration for the "bme680" platform, we can add a reference to the I²C Bus we'd like to use for this sensor using the "i2c_id" property.

So what does this look like for an ESP8266 device that only supports a single I²C Bus? Let's have a look:

 i2c:
- sda: 4
    scl: 5
    scan: true

sensor:
- platform: bme680
  address: 0x76

Since the ESP8266 only supports 1 I²C Bus, you don't have to specify an id, as it'll be the only one and that's why you also won't have to specify it in the configuration of the sensor. It'll just pick the one configured bus.

Posted on: Aug 3, 2023 Last updated at: Aug 3, 2023

Frequently asked questions

What is an I²C bus?
The I²C bus is a communication protocol that allows multiple devices to communicate with each other using a two-wire interface.
How does the I²C bus work on ESP32 and ESP8266?
On ESP32 and ESP8266, the I²C bus uses the SDA (data line) and SCL (clock line) pins to transmit and receive data between devices.
Why is the I²C bus important for ESP32 and ESP8266?
The I²C bus is important for ESP32 and ESP8266 because it allows the microcontroller to communicate with multiple peripheral devices, such as sensors and displays, using just two wires.
Can I connect multiple devices to the I²C bus?
Yes, you can connect multiple devices to the I²C bus by assigning unique addresses to each device. This allows for efficient communication between the microcontroller and multiple peripherals.
How do I configure the I²C bus on ESP32 and ESP8266?
To configure the I²C bus on ESP32 and ESP8266, you need to first initialize the I²C interface and set the desired clock frequency. Then, you can start communicating with the connected devices using the appropriate library and functions.
What is the maximum distance for the I²C bus?
The maximum distance for the I²C bus depends on factors like the quality of the wiring and the capacitance of the connected devices. However, generally, the I²C bus can reliably operate within a few meters.
What are some common uses of the I²C bus on ESP32 and ESP8266?
Some common uses of the I²C bus on ESP32 and ESP8266 include connecting sensors, displays, EEPROMs, real-time clocks, and other peripheral devices that use the I²C communication protocol.
Can I use the I²C bus with other microcontrollers?
Yes, the I²C bus is a widely used communication protocol, and you can use it with other microcontrollers as long as they support the I²C interface.
Is the I²C bus faster than other communication protocols?
The I²C bus is not the fastest communication protocol available, but it offers simplicity and ease of use. Its speed is typically around a few hundred kilobits per second, which is sufficient for many applications.
Where can I learn more about the I²C bus on ESP32 and ESP8266?
To learn more about the I²C bus on ESP32 and ESP8266, you can refer to the manufacturer's documentation, explore online tutorials and resources, or participate in community forums and discussions.