Cookie tin alarm

Step 1: Make it

What is it?

Has anyone been in your cookie tin? You can program your BBC micro:bit to act as an alarm to let you know! You will learn about selection, comparison logic, and the micro:bit's light sensor.

These two videos show you what you'll make and how to code it:

How it works

• The program turns the micro:bit’s LED display into a light sensor.
• Put your micro:bit into the tin you wish to protect. When the lid is opened, the light sensor detects a change in light level and triggers the alarm.
• The program uses an infinite loop to keep sensing the light level.
• Selection ('if... else') and comparison logic (> 30) are used so that if the light level is above a certain amount, an angry face appears on the display; else, it clears the screen.

What you need

• micro:bit (or MakeCode simulator)
• MakeCode editor
• battery pack

Step 2: Code it

1from microbit import *
2
3while True:
4    if display.read_light_level() > 30:
5        display.show(Image.ANGRY)
6    else:
7        display.clear()
8

Step 3: Improve it

• Adjust the program, removing the "else" part of the comparison, so that the angry face remains on the micro:bit’s display whatever the light level so that you can tell someone has opened your tin.
• Add an audible alarm using blocks from the music section of the MakeCode editor.
• Count how many times your tin has been opened by introducing a variable into the program.
• If you have two micro:bits, use the radio function to send you a signal as soon as your tin has been opened. Take a look at the light alarm project to find out how to do this.