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PCF8574 PCF8574AP digital input and output expander with i2c bus.

Changelog

• 18/04/2023: v0.0.2 Add static declaration for Px constants inside class.
• 14/04/2023: v0.0.1 Initial commit of stable version.

I try to simplify the use of this IC, with a minimal set of operations.

Tested with esp8266, esp32, Arduino, Arduino SAMD (Nano 33 IoT, MKR etc.), STM32 and rp2040 (Raspberry Pi Pico and similar)

PCF8574P address map 0x20-0x27 PCF8574AP address map 0x38-0x3f

Installation

To install the library execute the following command:

pip install pcf8574-library

Constructor: Pass the address of I2C

    from PCF8574 import PCF8574
    
    pcf = PCF8574(0x38, sda=21, scl=22)

To use interrupt you must pass the interrupt pin and the function to call when interrupt raised from PCF8574

    from PCF8574 import PCF8574
    
    def keyPressedOnPCF8574(pin):
        # Interrupt called (No Serial no read no wire in this function, and DEBUG disabled on PCF library)
        keyPressed = True
    
    pcf = PCF8574(0x38, sda=21, scl=22, interrupt_callback=keyPressedOnPCF8574, interrupt_pin=18)

You must set input/output mode:

    from machine import Pin
    from PCF8574 import PCF8574

    pcf.Pin(PCF8574.P0, Pin.IN)
    pcf.Pin(PCF8574.P1, Pin.IN, Pin.PULL_UP)
    pcf.Pin(PCF8574.P2, Pin.IN)
    pcf.Pin(PCF8574.P3, Pin.IN)
    
    pcf.Pin(PCF8574.P7, Pin.OUT)
    pcf.Pin(PCF8574.P6, Pin.OUT, 1)
    pcf.Pin(PCF8574.P5, Pin.OUT, 0)
    pcf.Pin(PCF8574.P4, Pin.OUT, 0)

then IC as you can see in the image has 8 digital input/output ports:

To read all analog input in one trasmission you can do (even if I use a 10millis debounce time to prevent too much read from i2c):

    digital_input = pcf.digital_read_all()
    
    print(digital_input.p0)
    print(digital_input.p1)
    print(digital_input.p2)
    print(digital_input.p3)
    print(digital_input.p4)
    print(digital_input.p5)
    print(digital_input.p6)
    print(digital_input.p7)
    
    array_input = pcf.digital_read_all_array()
    print(array_input)
    
    byte_input = pcf.digital_read_all_byte()
    print(bin(byte_input))

If you want to read a single input:

    digital_input = pcf.digital_read(PCF8574.P1)
    print(digital_input)

If you want to write a digital value:

    pcf.digital_write(PCF8574.P1, 1)

You can also use an interrupt pin: You must initialize the pin and the function to call when interrupt raised from PCF8574

    def callback(pin):
        now = utime.ticks_ms()
        global count
        count += 1
        print("Time: {} {}".format(now, count))
    
    
    pcf.attach_interrupt(18, callback)

For the examples I use this wire schema on breadboard: