Custom I²C Device


Custom components are deprecated, not recommended for new configurations and will be removed from ESPHome in a future release. Please look at creating a real ESPHome component and “importing” it into your configuration with External Components.

You can find some basic documentation on creating your own components at Contributing to ESPHome.


While we try to keep the ESPHome YAML configuration options as stable as possible, the ESPHome API is less stable. If something in the APIs needs to be changed in order for something else to work, we will do so.

Lots of devices communicate using the I²C protocol. If you want to integrate a device into ESPHome that uses this protocol you can pretty much use almost all Arduino-based code because the Wire library is also available in ESPHome.

See the other custom component guides for how to register components and make them publish values.

#include "esphome.h"

class MyCustomComponent : public Component {
  void setup() override {
    // Initialize the device here. Usually Wire.begin() will be called in here,
    // though that call is unnecessary if you have an 'i2c:' entry in your config

  void loop() override {
    // Example: write the value 0x42 to register 0x78 of device with address 0x21

I²C Write

It may be useful to write to a register via I²C using a numerical input. For example, the following yaml code snippet captures a user-supplied numerical input in the range 1–255 from the dashboard:

    - platform: template
    name: "Input 1"
    optimistic: true
    min_value: 1
    max_value: 255
    initial_value: 20
    step: 1
    mode: box
    id: input_1
    icon: "mdi:counter"

We want to write this number to a REGISTER_ADDRESS on the slave device via I²C. The Arduino-based looping code shown above is modified following the guidance in Custom Sensor Component.

#include "esphome.h"

const uint16_t I2C_ADDRESS = 0x21;
const uint16_t REGISTER_ADDRESS = 0x78;
const uint16_t POLLING_PERIOD = 15000; //milliseconds
char temp = 20; //Initial value of the register

class MyCustomComponent : public PollingComponent {
  MyCustomComponent() : PollingComponent(POLLING_PERIOD) {}
  float get_setup_priority() const override { return esphome::setup_priority::BUS; } //Access I2C bus

  void setup() override {
    //Add code here as needed

  void update() override {
  char register_value = id(input_1).state; //Read the number set on the dashboard
  //Did the user change the input?
  if(register_value != temp){
        temp = register_value; //Swap in the new value

The Component class has been replaced with PollingComponent and the free-running loop() is changed to the update() method with period set by POLLING_PERIOD. The numerical value from the dashboard is accessed with its id tag and its state is set to the byte variable that we call register_value. To prevent an I²C write on every iteration, the contents of the register are stored in temp and checked for a change. Configuring the hardware with get_setup_priority() is explained in Step 1.

See Also