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I2Cwrapper is a firmware framework which helps you implement Arduino based I2C target (slave) devices for control of non-I2C hardware. Supports plain Arduinos, ESP8266, ESP32, SAMD, STM32, and ATtiny ...

A while ago I received a couple of I/O port expander modules that use the I 2 C protocol. Using that Chinese module, you can use only the SDA and SCL pins of your Arduino, or any microcontroller ...