Button code lock

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import AngularServo, Button, LED
from time import sleep

CODE = ["A", "B", "B", "C"]                    # the secret code
keys = {"A": Button(5), "B": Button(6), "C": Button(13)}
bolt = AngularServo(17, min_angle=-90, max_angle=90)   # 0 = locked, 90 = open
red = LED(23)
green = LED(22)

def wait_key():
    while True:
        for name, button in keys.items():
            if button.is_pressed:
                while button.is_pressed:
                    sleep(0.02)
                return name
        sleep(0.02)

bolt.angle = 0
fails = 0
while True:
    entered = []
    while len(entered) < len(CODE):
        entered.append(wait_key())
        print("Keys so far:", len(entered))
    if entered == CODE:
        print("Correct code: UNLOCKED")
        fails = 0
        bolt.angle = 90
        green.on()
        sleep(5)
        bolt.angle = 0
        green.off()
        print("Locked again")
    else:
        fails += 1
        print("Wrong code. Failed tries:", fails)
        for _ in range(3):
            red.on()
            sleep(0.2)
            red.off()
            sleep(0.2)
        if fails >= 3:
            print("Too many tries: locked for 10 seconds")
            sleep(10)
            fails = 0

How the code works

• A dictionary keeps the three buttons by letter. wait_key() gives back the letter of the button that was pressed and released.
• The inner while loop collects four keys, then entered == CODE compares the two lists.
• After three wrong codes the lock stops answering for 10 seconds.

Parts to buy

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