from machine import Pin
from time import sleep  
 
KEY_UP   = const(0)
KEY_DOWN = const(1)
 
keys = [['1', '2', '3', 'A'], 
        ['4', '5', '6', 'B'], 
        ['7', '8', '9', 'C'], 
        ['*', '0', '#', 'D']]
 
cols = [19,13,12,23]
rows = [2,4,5,18]
 
row_pins = [Pin(pin_name, mode=Pin.OUT) for pin_name in rows]
 
col_pins = [Pin(pin_name, mode=Pin.IN, pull=Pin.PULL_DOWN) for pin_name in cols]
 
def init():
    for row in range(0,4):
        for col in range(0,4):
            row_pins[row].value(0)
 
def scan(row, col):
    row_pins[row].value(1)
    key = None
 
    if col_pins[col].value() == KEY_DOWN:
        key = KEY_DOWN
    if col_pins[col].value() == KEY_UP:
        key = KEY_UP
    row_pins[row].value(0)
 
    return key
 
init()
 
while True:
    for row in range(4):
        for col in range(4):
            key = scan(row, col)
            if key == KEY_DOWN:
                print("You pressed :", keys[row][col])
                sleep(0.3)