import machine
import time
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)

## Pin interrupt handler
#
# A function to handle pin interrupts
# Expects a machine.Pin type parameter
def interrupt_callback(pin):
    pass

def main():
    # a tiny sleep to allow the first print to be displayed
    sleep(0.01)
    print('Program starting')
    prev_binary_code = 0
    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)
    # code below here

if __name__ == "__main__":
    main()