Build your own I2C sensor

Since Raspberry Pi doesn’t have a built-in ADC (Analog to Digital converter) to read the voltage off from most of sensors, the best solution is to add I2C ADC chips and modules to your project. Pawel Spychalski faced this problem while building his own weather station that is based on Raspberry Pi. It collects various data and displays them on dedicated web page and Android app. Every few months he tries to add a new sensor to it. Last time it was a daylight sensor. He added this sensor to his system by using ATtiny85 and it was connected via I2C bus. ATtiny85 is a member of Atmel tinyAVR series which has 8-bit core and fewer features, fewer I/O pins, and less memory than other AVR series.”