Have you ever locked your door, only to turn back just to check if it’s really locked? I’ve done that dance a lot. Many would probably agree that the healthiest thing to do is to simply not double-check at all. After all, I’ve never actually forgotten to lock the door and my belongings are insured. Additionally, by repeatedly choosing not to check, I can rewire my brain over time and unlearn this habit.

But what if there’s a simpler fix, assuming you don’t mind something a little neurotic? In theory, I could create a small ritual to do right after locking the door, something that would help me remember I didn’t forget. Best of all, I’d only need a microcontroller and a few LEDs.

It works as follows: You lock the door and press the button. This triggers a yellow LED that stays lit for 15 seconds. That’s just enough time for me to reach the front door of the apartment building. A quick glance over my shoulder confirms I completed the habit before heading out. While I was at it, I added a red LED that blinks every few seconds. I figured if I’m already sticking a gadget to my door, I might as well make it look like a security device and maybe even deter intruders.

I’m still not great at C#, so I didn’t expect to do much better with MicroPython. But with some help from ChatGPT in regards to figuring out which libraries I needed and what they do, I managed to cobble together the code below. Surely there are plenty of ways to improve it, but for now, I’m just really happy with my first microcontroller and soldering project.

from machine import Pin, PWM, lightsleep
from time import ticks_ms, ticks_diff, ticks_add
import time

# Setup for LEDs
led_button = Pin(14, Pin.OUT)    # LED glows 15 seconds when button is pressed
led_dim = PWM(Pin(15))           # PWM for low glow

# PWM-Confiuguration
led_dim.freq(5000)
dim_duty = int(535 * 0.1)           

# Button-Setup
button = Pin(13, Pin.IN, Pin.PULL_UP)

# Timestamp for LED 14
led_on_until = 0

while True:
    now = ticks_ms()

    # LED on GPIO 15 short glow
    led_dim.duty_u16(dim_duty)
    time.sleep(0.2)
    led_dim.duty_u16(0)

    # Button press starts new 15 sec loop
    if button.value() == 0:
        led_on_until = ticks_add(now, 15000)

    # LED 14 on/off based on time
    if ticks_diff(led_on_until, now) > 0:
        led_button.on()
    else:
        led_button.off()

    # powersaving
    lightsleep(1800)