The PCF8574 is an 8 bits I/O port expander that uses the I2C protocol. Using this IC, you can use only the SDA and SCL pins of your Arduino board to control up to 8 digital I/O ports. A0,A1,A2 are address pins P0,P1,P2,P3,P4,P5,P6,P7 are digital...
PCF8574