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Available library: PCF8575
_ I2C address: 0x20 (default), can be modified by installing A1 and A2.
_ Working voltage: 2.5 - 5.5V DC
_ Working current: 100mA (MAX)
_ The PCF8575 is controlled through an I2C interface and features 16-bits of quasi-bidirectional input/output pins.
_ Open-drain interrupt output pin for input change interrupt.
_ The PCF8575 IO expander board is great for R3 and other MCU to control simple relay, buzzer, button, led.