Have you run out of I/O pins? This great module allows the to expand up to 16 I/O using only two I/O for control The PCF8575 is controlled through an I2C interface and features 16-bits of quasi-bidirectional input/output pins. On board 3.3V level converter circuit, if you donot solder VCC- pad, the PCF8575 level is 3.3V. If you solder it, the level will be the same with VCC available library: PCF8575 Working voltage: 2.5 - 5.5V DC Working current: 100mA(MAX) I2C address: 0x20(default),can be modified by soldering A1 and A2 pads. 16 individually addressable pins. Each pin configurable for input or output Open-drain interrupt output pin for input change interrupt. Great for R3 and other MCU to control simple relay, buzzer, button, led. Size: 4 x 2.1cm/1.57 x 0.83inch Condition: New Type: Smart Electronics Model Number: PCF8575 Application: Electronic experiment Operating Temperature: -40 ~ +85 color:As shown :PC+Metal Package Contents: 5 x PCF8575 IO Expander Module Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.