Arduino 328 series panel IO port is only 20, plus some sensor, SD card Han, relay modules and more, IO port is not enough, 
the original 2004 screen requires 7 IO port can drive up, we have developed This module can help you save five IO ports, we send arduino library

Product parameters: 
1. supply voltage: +5 V 
2. supports the I2C protocol 
3. with backlight and contrast adjustment potentiometer 
4. 4 line out easier.