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micro:bit Wireless Intruder Alarm

In this assignment you will work with a partner to program two micro:bits to create a wireless intruder alarm that will warn you when someone steps on a home-made pressure sensor.

Each partner will write a program for their micro:bit. One person will program their micro:bit to act as the sending device that is triggered by the pressure sensor. The other person will program the receiver that activates the alarm. The alarm could use the speaker to create a sound, trigger an LED, or even activate a servo to "whack" the intruder. In both programs you will need to set the group to the same number from 0 to 255.

You may find slides 141 - 145 of the slide presentation helpful in completing this assignment.

Program requirements

  • Your programs must use the micro:bit's radio to send and receive messages
  • Each person will submit the Python code for their program (either the sender or receiver) and an animated gif showing the two programs running to Google Classroom

Build the Pressure Sensor

Cut out a small piece of cardoard and fold it in half. Glue two squares of foil on one side of the fold, and a third on the other so that when the cardboard is folded the foil completes the circuit. Connect pin 0 and ground to the sensor as shown below:

Write the sending code on one micro:bit

  1. Add import radio to the top of your program
  2. Add radio.on() and radio.config(group = some number) before the while True:. For the group number, choose a number between 0 and 255
  3. Inside of the while True: write an if statement using pin0.read_analog() to detect when the pressure switch is closed. The reading will be between 0 and 1027. If the switch is closed, the reading will be a low number. If the switch is open, the reading will be a high number. If the switch is closed, send a message using radio.send("a message"), otherwise send radio.send("a different message").

Write the receiving code on the other micro:bit

  1. Add import radio to the top of your program
  2. Add radio.on() and radio.config(group = some number) before the while True:. For the group number, be sure to use the same group number as the sending code
  3. Inside of the while True: write an if statement using radio.receive(). If the the message indicates the pressure switch is closed, trigger the alarm.

Extensions

If you have extra time, you can add multiple sensors each sending its own message, e.g. ‘room1’, ‘room2’ and have the alarm show where the intruder is. You could also try different designs for the pressure switch. For example, place a foam pad inside it if is being triggered too easily. You could also 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! Have fun and be creative, your alarm doesn't have to work like any other.

Samples of Student Work

Noel
Patrick
Isaac
Alvin
Evangeline