Step 1: Make it
What is it?
Create a wireless intruder alarm that will warn you when someone steps on a home-made pressure sensor.
How it works
- Flash the sensor program onto a micro:bit.
- Make a pressure input switch out of cardboard and tin foil like in the picture. Fold it over and place it under a rug or carpet. You may need to add some foam to keep each side apart. Connect the two foil pads on one side to pins 0 and GND on the sensor micro:bit. When you step on it, the foil on the top completes an electrical circuit, and it sends an ‘intruder’ radio message.
- Flash the alarm program on to the other micro:bit (the alarm) and attach a buzzer or speaker to pin 0 and GND if you have one. When it receives the ‘intruder’ message it shows an angry face on the LED display and plays an audible alarm sound. Press button A to clear the display.
What you need
- 2 micro:bits and at least 1 battery pack
- 2 crocodile clip leads
- tin foil, scrap cardboard, glue, scissors, foam
- optional buzzer, amplified speaker or headphones and 2 crocodile clip leads
Step 2: Code it
Sensor / transmitter:
Alarm / receiver:
Step 3: Improve it
- Add multiple sensors each sending its own message, e.g. ‘room1’, ‘room2’ and have the alarm show where the intruder is.
- Try different designs for the pressure switch. For example, place a foam pad inside it if is being triggered too easily.
- You could make a rain alarm using two tin foil pads very close together – if they get wet, they will trigger the alarm. Be sure not to get your micro:bit wet though!
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