We are surrounded by sound everyday, from the music we listen to, the sounds of nature, conversations with friends etc.
Sound also plays a major role in many electronic applications.
A Piezo Buzzer is one of the many ways you can add an audio element to your project.
They generate beeps and tones when a voltage is applied to it and can be found in many applications such as doorbells, children’s toys, musical instruments, smoke alarms etc.
On the flipside of producing sound, is the ability to record or amplify sound.
Microphones are devices that capture sound waves and convert them into an electrical signal.
The signal can then be amplified or converted to a digital signal depending on the needs of the application.
But, can you use a piezo buzzer as a microphone? Yes, a piezo buzzer can be used as a microphone. Normally the piezo buzzer produces a sound when voltage is applied to it. When used in reverse, a sound can cause the piezoelectric disk of the buzzer to oscillate thus producing a voltage at the terminals of the piezo buzzer. This signal can then be amplified or recorded the same way a microphone does.
Note, additional circuitry will be needed to make a microphone using a piezo buzzer.
What is a piezo buzzer
To better understand how a piezo buzzer can be used as a microphone, let’s take a closer look at how it works.
Below is what a typical buzzer looks like when you buy it. You might have a few, or you might have seen them before.
If we were to open the piezo buzzer and take a look inside, we would find the lower housing, drive circuit, piezoelectric disk and upper housing.
The main attraction of this setup is the Piezoelectric disk. Hence why it is called a piezo buzzer.
The two faces of the piezoelectric disk have wires attached to them and when a voltage is applied to these wires, the disk oscillates.
Oscillation of the disk is what causes sound.
Varying the frequency of the voltage applied will cause the piezoelectric disk to oscillate at different frequencies hence generating different pitches of sound.
The oscillation of the piezo disk (when a voltage is applied to it) can be visualised as shown in the diagram above.
How a microphone works
Let’s switch our view to a microphone.
Microphones are used in many different applications from your favourite singer singing on stage, recording audio, podcasts, making a speech to an audience and so much more.
They are a great way of amplifying your voice over great distances without having to shout at the top of your lungs.
But, it isn’t just good for amplifying audio, they can be used to record it too.
Audio can be captured by microphone which can then be converted to a digital signal (which is done by a separate circuit). The digital signal can then be stored for later use (like a digital recorder), or modified (like a voice changer).
If we were to open up the microphone, you would be able to see the circuit as pictured below:
The main components of the microphone are;
- Diaphragm
- Coil
- Permanent magnet
When you speak into the microphone, sound waves come in contact with the diaphragm causing it to
oscillate.
This causes the coil (which is attached to the diaphragm) to oscillate as well.
The permanent magnet creates a magnetic field and when the coil moves back and forth through this magnetic field an electric current is produced.
This electric current can then be amplified or recorded as pleased.
Difference between a piezo buzzer and microphone
Now that we know how each of these devices works we can look at their main differences and then later see how we can use the piezo buzzer as a microphone.
The inner circuits of both devices are very similar, but they just work in opposite directions.
A Piezo buzzer is supplied a voltage that causes its diaphragm (in this case a piezoelectric disk) to vibrate which in turn produces sound.
Microphones work the opposite way.
Sound waves cause the diaphragm to oscillate which then produces a voltage.
Can a piezo buzzer be used as a microphone?
Now we have what we need to answer the question of whether you can use a piezo buzzer as a microphone.
So, to create a microphone we essentially need to convert sound waves into an electrical signal.
The beauty of the piezoelectric disk is that it has the ability to work in both directions.
When a voltage is applied to it it produces sound.
But, it can also be used to produce voltage when force or pressure is applied to it.
This is great news for us since sound waves are a form of pressure which can cause the disk to deform and thus produce a voltage.
However, just talking into the piezoelectric disk is not going to achieve much. You will need to attach it to a dedicated circuit which can amplify the voltage signals (as they are going to be quite weak).
Piezo buzzer microphone circuit
Below is one of the circuits you can use to create a microphone using a piezo buzzer.
To make the piezo buzzer more effective, remove the piezoelectric disk from the casing so it is bare. This way sound waves won’t be obstructed by the plastic of the housing.
Is it effective to use a piezo buzzer as a microphone?
So, a piezo buzzer can be used as a microphone. But, how effective it is at capturing sound waves is another story.
The diaphragms in microphones are designed to be sensitive enough to capture sound waves from a variety of distances and angles.
Piezoelectric disks are less sensitive compared to diaphragms used in microphones, so it might be harder to pick up sound waves.
If you are using the microphone to amplify sound, it might not be too much of a problem, but if you are using it as a voice recorder this might be an issue as recording sound might be a bit harder as not all audio might be captured.
