Create a Light-sensitive Alarm with micro:bit

Learn to use the buzzer module and make your own light-sensitive alarm!

Written By: Cherie Tan

Difficulty

Easy

Steps

A buzzer is an audio signalling device. There are two types of buzzers, a passive buzzer and an active buzzer. In this guide, we will learn to differentiate between the two, then connect a passive buzzer module to the micro:bit and get it to play a song and change its bpm with a button press.

A light dependent resistor will also be added to the circuit, to create an alarm clock that automatically rings when it gets bright.

After completing this guide, you will understand the basics involved in using a buzzer, and can go on to make your own creations.

Step 1 The Modules

Let's take a closer look at the light-dependent resistor module as well as the buzzer module. The light-dependent resistor module has four pins:

3.3V : While 'VCC' stands for Voltage Common Collector, we'll connect the VCC pin to 3.3V on the micro:bit

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.

Note: 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.

DO: Digital Output

AO: Analog Output

The buzzer module has three pins:

3.3V : While 'VCC' stands for Voltage Common Collector, we'll connect the VCC pin to 3.3V on the micro:bit

I/O: Input/Output

GND

There are two buzzer modules in the kit. Open up the 'Day 15' bag as well, one of the buzzer modules only has a + on the top as shown in the third image, while the other has 'HYDZ' written on it.

One is a passive buzzer while the other is an active buzzer. An active buzzer has additional circuitry in it, and it can generate its own tone. On the other hand, a passive buzzer is like a speaker, where a changing input signal produces the sound. If you put them side by side, the active buzzer is the slightly taller one.

Step 2 Connect module to breadboard

Step 3 Connect + to VCC

Step 4 Connect GND to GND (light-dependent resistor)

Step 5 Connect P5 to DO

Step 6 Connect P1 to AO

Step 7 Connect + to VCC (Buzzer module)

Step 8 Connect P0 to I/O

Step 9 Connect GND to GND (Buzzer module)

Step 10 Connect 3.3v to +

Step 11 Test out the two buzzer modules

basic.forever(function () {
    pins.digitalWritePin(DigitalPin.P0, 0)
    basic.pause(1000)
    pins.digitalWritePin(DigitalPin.P0, 1)
    basic.pause(1000)
})

Before we begin, let's take a look at the difference between the two buzzer modules.
Use this same MakeCode for both buzzers, swapping them out one after the other. Copy and paste this code to the Javascript interface.

Upload this MakeCode to the Micro:bit to hear the difference.

Using the passive buzzer module, you will hear a faint ticking sound as it does not produce its own tone. The active buzzer module will produce a loud beep. In the following MakeCode examples, we will be using the passive buzzer module.

Step 12 Power up sound

music.beginMelody(music.builtInMelody(Melodies.PowerUp), MelodyOptions.Forever)

First, open up MakeCode editor

Click on 'New Project'

Copy and paste this code into the Javascript interface

Step 13 On button A press

input.onButtonPressed(Button.A, function () {
    music.changeTempoBy(5)
})
music.beginMelody(music.builtInMelody(Melodies.Nyan), MelodyOptions.Forever)

We can also change the bpm (beats per minute) of the tune. Replace the existing code with this in the Javascript interface.

Step 14 Add variable 'lightVal'

let lightVal = 0
basic.forever(function () {
    lightVal = pins.analogReadPin(AnalogPin.P1)
})

You can play all sorts of sounds with a buzzer module and a micro:bit. But what about making a light-sensitive alarm clock with it? So let's add a light dependent resistor to the circuit. The alarm will automatically sound when it gets bright enough.

We will set a threshold level value for this brightness level. Firstly, create a variable for 'lightVal' which is short for light value using: let lightVal = 0

This will store the analog value rather than digital value (1 or 0) of the light level.

Step 15 Show number

let lightVal = 0
basic.forever(function () {
    lightVal = pins.analogReadPin(AnalogPin.P1)
    basic.showNumber(lightVal)
})

Replace the code with the following in the Javascript interface

To set the threshold level, let's take a look at how bright it is around your surroundings using:

basic.showNumber(lightVal)

Step 16 Conditional statement

let lightVal = 0
basic.forever(function () {
    lightVal = pins.analogReadPin(AnalogPin.P1)
    basic.showNumber(lightVal)
    if (lightVal < 600) {
        music.beginMelody(music.builtInMelody(Melodies.PowerUp), MelodyOptions.Once)
    }
})

Replace the code with the following in the Javascript interface

The loop will run forever until the micro:bit is turned off.

Try changing the tune to a longer one such as 'birthday' or 'entertainer' then upload this code to your Micro:bit now. You might realise that only part of the tune plays. To play a full tune, use the next MakeCode.

Step 17 Play the whole tune

let lightVal = 0
let playingMusic = 0
music.onEvent(MusicEvent.MelodyEnded, function () {
    playingMusic = 0
})
playingMusic = 0
basic.forever(function () {
    lightVal = pins.analogReadPin(AnalogPin.P1)
    if (lightVal < 600 && playingMusic == 0) {
        music.beginMelody(music.builtInMelody(Melodies.Entertainer), MelodyOptions.Once)
        playingMusic = 1
    }
    basic.showNumber(lightVal)
})

Step 18 Use the active buzzer

let lightVal = 0
basic.forever(function () {
    lightVal = pins.analogReadPin(AnalogPin.P1)
    basic.showNumber(lightVal)
    if (lightVal < 600) {
        pins.digitalWritePin(DigitalPin.P0, 0)
        basic.pause(500)
        pins.digitalWritePin(DigitalPin.P0, 1)
        basic.pause(500)
    }
})

Optionally, if you want to use the active buzzer instead, you can. Copy and paste this code into the Javascript interface, replacing the previous code.

Step 19 Upload the code

To upload the code to the micro:bit, first connect the micro:bit to the computer via microUSB cable

Click on the 'Download' button and the hex file will be automatically downloaded to your 'Downloads' folder

Drag and drop the downloaded .hex file to the MICROBIT drive

Leave the micro:bit alone for a few seconds as it blinks. The code is uploading.

Once powered up, the buzzer will sound the alarm when it gets bright. Cover the light dependent resistor with your hands, and the buzzer will stop making sound!