Lesson video

Hello, I'm Mrs. Taylor, and thank you for joining me for our lesson today.

Our lesson today is buzzers, and this is part of the systems approach to design sustainable futures unit.

The outcome.

I can explain the function of different buzzers and use them as output components in a control system.

There are three keywords.

Electromechanical, an electrically operated mechanical device.

Piezoelectric, a smart material which creates a small amount of electricity when pushed.

And electromagnet, a magnet made using a coil, a core, and a power supply.

There are two parts to our lesson today, electromechanical buzzers and piezoelectric buzzers.

We begin with electromechanical buzzers.

Sound can be an output from a control system.

Bells and buzzers are output devices which convert an electrical signal into a sound.

Bells and buzzers are often used for alerts and alarms. For example, an alarm clock.

A doorbell uses an electromagnet to create the movement of a clapper.

The clapper repeatedly hits a bell when current passes through the electromagnet.

Electromechanical bells and buzzers use a magnetic coil to create a magnetic field.

An electromagnet is a magnet that can be turned on with an electric current, and turned off.

Here we can see a diagram of an electric bell.

The switch is pressed which connects the circuit.

The magnetic coil becomes magnetised.

The iron armature is attracted to the electromagnet.

And the clapper hits the bell.

Here we have a check for understanding.

Read and complete the sentence.

Pause the video.

Fabulous.

Let's check.

A doorbell uses an electromagnetic coil to strike a bell with a clapper.

Well done.

Electromechanical buzzers work in a similar way to an electric bell.

The sound is created with the armature hitting the magnet instead of a bell and clapper.

The armature is a piece of metal which is magnetic, so is drawn to the magnetic coil when current passes.

Here we can see a picture of an electromechanical buzzer.

How an electromechanical buzzer works.

First, we look at the circuit, which has a switch and a battery.

The buzzer itself has a spring, a magnet, a metal armature, and an electromagnetic coil.

Number one, when the circuit is disconnected and the switch is open, there is no current flowing through the electromagnetic coil.

The armature is held above the electromagnetic coil by a spring, in a resting position.

Number two, when the circuit is connected and current flows through the electromagnetic coil, it becomes magnetised.

The armature is then pulled towards the electromagnetic coil.

Number three, the armature has moved towards the electromagnetic coil and the contacts have opened, current cannot flow.

Number four, the armature is pulled back to its resting position by the spring.

The noise is the sound of the armature hitting the magnet.

Here we have a check for understanding.

In an electromechanical buzzer, which part moves to create the sound? Is it A, the armature, B, a clapper, or C, a bell? Pause video and have a go.

Great.

Let's check.

That's right.

It's A.

The armature.

Well done.

Polarity is the directional flow of electrons from one pole to another.

Electromechanical buzzers are polarised, which means they must be positioned in the circuit the correct way around.

Here we can see inside the buzzer.

In this example, there is not a spring, as the metal armature acts as the spring itself.

There is a metal armature and the electromagnetic coil.

And now we see a side view of the same electromechanical buzzer.

And we can see the metal armature with a space between that and the electromagnetic coil, as this buzzer is currently not connected, and therefore there is no current flowing through.

Data sheets show the specific details of components.

Here is a data sheet for an electromechanical buzzer.

The operating voltage is between four and six volts, the rated current is 25 milliamps, the minimum sound output is 75 decibels, and the resonant frequencies are 400 hertz.

The operating voltage is a voltage at which the buzzer will work.

The rated current is the maximum current the buzzer can safely handle.

The minimum sound output, which is measured in decibels.

Resonant frequency is the frequency a material will vibrate.

We now move to task A.

Draw and annotate a diagram to explain an electromechanical buzzer.

Pause the video and have a go.

Wonderful.

Let's have a look at some of the answers you may have come up with.

Your answer may look something like this.

A diagram with the switch and battery labelled, as well as the spring, magnet, metal armature, and electromagnetic coil labelled.

And your description may be something similar to this.

For part one, when the circuit is disconnected and the switch is open, there is no current flowing through the electromagnetic coil.

The armature is held above the electromagnetic coil by a spring, in a resting position.

Stage two, when the circuit is connected and current flows through the electromagnetic coil, it becomes magnetised.

The armature is then pulled towards the electromagnetic coil.

Part three, the armature has moved towards the electromagnetic coil and the contacts have opened, current cannot flow.

And part four, the armature is pulled back to its resting position by the spring.

The noise is the sound of the armature hitting the magnet.

Well done.

We now move to the second part of our lesson, piezoelectric buzzers.

Piezoelectric material is a smart material.

Smart materials react to a stimulus.

Piezo comes from the Greek word piezein, which means to press or to squeeze, and electric simply means electric.

Piezoelectric materials generate a small electrical charge when you press, squeeze, or bend them.

An example of this is in shoes which light up when pressure is applied.

Piezoelectric materials work the other way too.

They can move or make vibrations when electricity is passed through them.

When current passes through piezoelectric material, it flexes.

The buzzer sound in a piezoelectric buzzer is the piezoelectric material flexing rapidly as current passes through.

Here we have a check for understanding.

What does the piezoelectric material do in a piezoelectric buzzer? Does it, A, turn around, B, flexes, or C, stays still? Pause the video and have a go.

Great.

Let's check.

That's right.

It's B.

It flexes.

Well done.

This table summarises the data sheets of two different buzzers.

Electromagnetic buzzers operate at lower voltages and higher currents than piezoelectric buzzers because their coils need more current to produce a strong magnetic field.

The resonant frequency is the frequency a material will vibrate.

Electromechanical buzzers rely on mechanical movement, which is slower than the vibrations of piezoelectric material.

Electromechanical buzzers are used in toys, games, timers, and door buzzers, when a loud buzz is required.

Piezoelectric buzzers are used in smoke and gas detectors, microwave ovens and appliances, digital watches and clocks, and hearing aids.

Piezoelectric buzzers are used when compact and efficient sound is required.

Here we have a check for understanding.

True or false? Electromagnetic buzzers operate at lower currents and higher voltages than piezoelectric buzzers.

Pause the video and have a go.

Great.

Let's check.

That's right.

It is false.

Electromagnetic buzzers operate at lower voltages and higher currents than piezoelectric buzzers because their coils need more current to produce a strong magnetic field.

Well done.

Here we can see a piezoelectric buzzer connected to a micro:bit.

The programme uses two if statements.

If the temperature is equal to or greater than 25 degrees C, then through pin 0, an analogue pitch at 600 hertz sounds.

If the temperature is equal to or less than six degrees Celsius, then through pin 0, and analogue pitch at 300 hertz sounds.

Here we have task B.

There are six parts.

Part one, describe what piezoelectric material is and how it functions.

Part two, explain the difference between electromagnetic buzzers and piezoelectric buzzers.

Part three, in Tinkercad, create a programme to sound a buzzer when the temperature in the greenhouse reaches over 30 degrees.

Part four, simulate and explain the programme.

Part five, develop the programme to make different sounds for different light levels.

And part six, simulate and explain the programme.

Pause the video and have a go.

Great.

Let's have a look at some of the answers you may have come up with.

For part one, you may have said, "Piezoelectric material is a smart material.

Smart materials react to a stimulus.

Piezoelectric materials generate a small electric charge when you press, squeeze, or bend them.

They also flex when current is passed through them." For part two, you may have said, "Electromagnetic buzzers operate at lower voltages and higher currents than piezoelectric buzzers because their coils need more current to produce a strong magnetic field.

They also operate at lower frequencies as they rely on mechanical movement, which is slower than the vibrations of piezoelectric material.

Piezoelectric buzzers are used in products that require a compact and efficient buzzer, such as smoke alarms." For part three and four, you may have said, "I used an if and else command to create a programme which turned on the piezoelectric buzzer, which was connected to pin 0 when the temperature in the greenhouse was more than 30 degrees Celsius.

I simulated and tested this using the sliders to control the temperature.

I don't like the sound, so it would be good as an alert to open the windows and cool down the greenhouse." For part five and six, you may have said, "It was great fun testing out the different sounds by changing the analogue pitch and time.

I used two if statements, one for if the light levels were above 150 and one for if the light levels were below 25.

I set the analogue pitch and time to be completely different, so there would be a different alert sound for each light level." Well done.

Here we have a summary of our learning today.

Buzzers are output devices which convert an electrical signal into a sound.

There are two types of buzzers, electromechanical and piezoelectric.

An electromagnetic coil is used in an electromechanical buzzer to move a piece of metal which makes the sound.

In a piezoelectric buzzer, the smart material flexes and makes the sound.

Changing the frequency of the movement in the buzzer changes the pitch we hear.

Thank you and well done.