If you just don't have enough digital I/O pins on your Arduino to interface with all your sensors and controls, you might want to look at using the I2C bus to connect a few port expander chip PCA8574AD have 8 digital I/O bits and can be set to addresses 0x38-0x3F respectively.The I2C bus on the Arduino uses SCL, SDA, a couple of pull up resistors and the Wire library.You can connect more expander module. More 8 modules. Just change adress of each module.On back side of board have instruction.If you need more connecting modules, pls cut off the connection of pull-up resistor on back side of board. Only 1 board need pull-up resistor.
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