I2C Example

This example will show you how to use I2C module by running two tasks on i2c bus:
- read external i2c sensor, here we use a BH1750 light sensor(GY-30 module) for instance.
- Use one I2C port(master mode) to read or write the other I2C port(slave mode) on one ESP32 chip.
Pin assignment:
- slave :
  - GPIO25 is assigned as the data signal of i2c slave port
  - GPIO26 is assigned as the clock signal of i2c slave port
- master:
  - GPIO18 is assigned as the data signal of i2c master port
  - GPIO19 is assigned as the clock signal of i2c master port
Connection:
- connect GPIO18 with GPIO25
- connect GPIO19 with GPIO26
- connect sda/scl of sensor with GPIO18/GPIO19
- no need to add external pull-up resistors, driver will enable internal pull-up resistors.
Test items:
- read the sensor data, if connected.
- i2c master(ESP32) will write data to i2c slave(ESP32).
- i2c master(ESP32) will read data from i2c slave(ESP32).