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 ...

The PCF8574_LH library provides a simple interface for controlling the PCF8574 I/O expander using the I2C communication protocol. It allows you to read and write values to the PCF8574's registers, ...