The IIC/I2C serial interface adapter module makes interfacing with the 1602 and 2004 LCD displays allot easier by minimizing the number of wires needed to connect a LCD to your controller (e.g. Arduino). This is done by translating serial input over just a few wires into parallel input that will then be sent to the LCD module. The pins are also designed to perfectly match HDHD44780-based LCD displays. This therefore makes it easy to simply solder them directly onto the back of the LCD.
The board makes use of a PCF8574 based controller chip, which is capable of taking inputs from SDA and SCL pins and translating it to parallel output over 8 quasi-bidirectional I/O Ports and 3 Address Inputs. And with just two data lines, in addition to the Vcc and Vss lines, you can operate entire displays and arrays of pixel from your controller while still having enough pins left to communicate to your other sensors.