PCF8591 - 8 Bit I2C ADC & DAC Module
Have you ever wanted more analog input pins on your Arduino project, but not wanted to fork out for a Mega? Or would you like to generate analogue signals? It solves both these problems as it has a single DAC (digital to analogue) converter as well as four ADCs (analogue to digital converters), all accessible via the I2C bus. If the I2C bus is new to you, please familiarise yourself with the readings here before moving forward.