Reed Switch with micro:bit

Learn to use a reed switch module and create a security alarm

Written By: Cherie Tan

Dash icon
Steps icon
A reed switch is an electrical switch which is operated when a magnetic field is brought near to it. 

In this guide, you will learn how to connect it to the micro:bit and turn an LED as well as an alarm on and off. We will then test it with a magnet.

Complete this guide and use it to create a security alarm system. Most alarm systems use a magnetic reed switch on doors and windows. They may come in different forms and styles, but they operate using the same principle!

Step 1 The Module

The reed switch module has three pins:

Digital Output (DO)

GND: In electronics, we define a point in a circuit to be a kind of zero volts or 0V reference point, on which to base all other voltage measurements. This point is called  ground or GND.

3.3V  :  'VCC' stands for Voltage Common Collector. We'll connect the VCC pin to 3.3V on the micro:bit

Voltage is the difference in potential between two points. As it is difficult to talk about voltage without a reference point, we need another point to compare it to. 

Step 2 Connect module to breadboard

Step 3 Connect P1 to DO

Step 4 Connect GND to GND

Step 5 Connect + to VCC

Step 6 Connect GND to LED (Negative lead)

Step 7 Add a resistor

Step 8 Connect P2 to resistor

Step 9 Connect + to VCC (Buzzer module)

Step 10 Connect P0 to I/O

Step 11 Connect GND to GND (Buzzer module)

Step 12 Connect 3.3V to +

Step 13 Show number

let signal = 0
pins.setPull(DigitalPin.P1, PinPullMode.PullUp)
basic.forever(function () {
    signal = pins.digitalReadPin(DigitalPin.P1)
    if (signal == 0) {
        music.playTone(262, music.beat(BeatFraction.Whole))
    } else if (signal == 1) {
Let's get started with programming the micro:bit using MakeCode editor
Click on 'New Project'
Copy and paste the following code into the Javascript interface

Step 15 Upload the hex file

Connect the micro:bit to your computer using a microUSB cable
Click on the 'Download' button in MakeCode editor
Find the downloaded hex file in your Downloads folder
Open up Finder on the MacOS or Explorer on Windows, and drag the hex file into MICROBIT under 'Devices' on the macOS.
Let the micro:bit blink as the program uploads to completion.