import machine
from utime import sleep

s0 = machine.Pin(27, machine.Pin.OUT)
s1 = machine.Pin(28, machine.Pin.OUT)
mux_in = machine.Pin(26, machine.Pin.IN, machine.Pin.PULL_DOWN)

prev_binary_code = 0
while True:
    binary_code = 0
    for selector_val in range(4):
        # | S1 | S0 |  D  |
        # |----|----|-----|
        # |  0 |  0 |  0  |
        # |  0 |  1 |  1  |
        # |  1 |  0 |  2  |
        # |  1 |  1 |  3  |
        #
        # from the mux truth table that shows 
        # which Data Input is selected based on the select values
        # we can deduce how to formulate S0 and S1

        # s0: 0 - 1 - 0 - 1, remainder of the select-count from /2
        # the modulo operation
        # 0 % 2 = 0
        # 1 % 2 = 1
        # 2 % 2 = 0
        # 3 % 2 = 1
        s0.value(selector_val % 2)

        # s1: 0 - 0 - 1 - 1, integer part of select-count /2
        # 0 // 2 = 0
        # 1 // 2 = 0
        # 2 // 2 = 1
        # 3 // 2 = 1
        s1.value(selector_val // 2)
        sleep(0.020)
        # (10^1 * digit_1) + (10^0 * digit_0)
        # example: 28 -> (10^1 * 2) + (10^0 * 8)
        # (2^n * input_n) + ... + (2^1 * input_1) + (2^0 * input_0)
        binary_code += (pow(2, selector_val) * mux_in.value())
    if binary_code != prev_binary_code:
        print(f'decimal representation: {binary_code}')
        prev_binary_code = binary_code
    sleep(0.100)