from machine import Pin
import time

rows = [Pin(7, Pin.OUT),
        Pin(6, Pin.OUT),
        Pin(5, Pin.OUT),
        Pin(4, Pin.OUT)]

cols = [Pin(3, Pin.IN, Pin.PULL_UP),
        Pin(2, Pin.IN, Pin.PULL_UP),
        Pin(1, Pin.IN, Pin.PULL_UP),
        Pin(0, Pin.IN, Pin.PULL_UP)]

keypad_layout = [
    ['1', '2', '3', 'A'],
    ['4', '5', '6', 'B'],
    ['7', '8', '9', 'C'],
    ['*', '0', '#', 'D']
]

def scan_keypad():
    for i in range(4):
        for j in range(4):
            if i == j: rows[j].value(0)
            else: rows[j].value(1) 
        for col_num, col in enumerate(cols):
            if col.value() == 0: return keypad_layout[i][col_num]
    return None

while True:
    key = scan_keypad()
    if key: print("Key pressed:", key)
    time.sleep(0.01)