I2C Adapter Board, fits right on the back of most LC display modules with 1 x Hitachi HD44780 or compatible display controller. The on board PCF8574 or PCF8574A 8-bit I/O expander encodes the signals for the 4 data bits, the read/write select, register select, the enable signal, and the backlight on signal. The supported I2C addresses depend on the version of the expander IC – please refer to the manufacturer PDF or find plenty of information online (for example Arduino forum). When connected to an Arduino, for example, the function of every pin can be easily modified by changing the parameters in your Arduino sketch. Additional features: – on board transistor to drive a LED backlight – 3 solder jumpers for address selection – jumper to turn on backlight continuously – generator for contrast voltage – contrast control potentiometer The pinout on the board is as follows: 1 – VSS (ground) 2 – VDD (+5V) 3 – contrast voltage 4 – RS (register select) 5 – R/W (read/write) 6 – Enable 11 – Data 4 12 – Data 5 13 – Data 6 14 – Data 7 15 – LED[+] 16 – LED [-] Pins 7, 8, 9 and 10 are not connected because not used in 4-bit data mode. Additional circuit design information: The I2C bus on development boards like the Arduino series of boards doesn’t have the necessary pull-up resistors already installed. To make a I2C connection happen, you will need pull-up resistors from VDD to SDA and SCL. The value of these resistors is not critical, as long the wires are not too long, the data rate high, or many devices connected to the same bus. For just 1 or 2 displays on 5V logic level is a value of 1.8k to 12k a good choice.