from machine import Pin
import utime, time

keys = [[1,     2,   3,  'A'],
        [4,     5,   6,  'B'],
        [7,     8,   9,   'C'],
        ['*',   0,  '#', 'D']]
rows = [26, 22,21,20]     
columns = [19,18,17,16]   
col_pins = []
row_pins = []
for x in range(0,4):
    row_pins.append(Pin(rows[x], Pin.OUT))
    col_pins.append(Pin(columns[x], Pin.IN, Pin.PULL_DOWN))
print("Please enter a key from the keypad")
while True:
    for row in range(4):
        for col in range(4):
            row_pins[row].value(1)
            if col_pins[col].value():
                print("You have pressed:", keys[row][col])
                while col_pins[col].value():  # 계속 눌려져 있을 때 오류 방지
                    pass
                utime.sleep(0.3)
        row_pins[row].value(0)
    time.sleep(0.2)