Thursday, December 15, 2011

Simple Buzzer Circuit - Piezo Electric Buzzer Explained

In this article we will learn how to make a very simple piezo electric buzzer using hardly any electronic components.
Just a single transistor, a coil, a piezo buzzer are enough to make it “buzz” or rather “twit” for you, with an output that may be quite ear piercing.

Circuit Description:

The simple buzzer circuit described here actually works in a quite unique way. Instead of the normal working concept employed by other forms of oscillators which require resistor and capacitor networks for generating the oscillations, this circuit use inductive feedback for the required operations.



Simple Buzzer Circuit


Referring to the above simple piezo buzzer circuit we find that the transistor T1 along with the inductor forms the heart of the circuit. Basically the coil which is specifically called the buzzer coil, is in fact positioned for amplifying the created oscillations while the actual feed back is provided by the center tap of the three terminal piezo element used for the present application.

When a voltage is introduced in the circuit, the transistor conducts, operating the piezo element across the buzzer coil, however this also leads to the grounding of the base of the transistor through the center tap of the piezo element, this instantly switches off the transistor and in turn the piezo also switches off, releasing the base of the transistor.

 The transistor reverts to its original state and the cycle repeats, generating oscillations or the required “buzzing” frequency.

The center tap from the piezo transducer plays an important role in sustaining the oscillations and therefore in this particular design we need a three terminal piezo rather than a two terminal one.

The oscillations produced at the collector of the transistor is dumped into the coil, saturating the coil with magnetic inductions. The coil kicks back the stored energy during the oscillations, magnifying the generated AC across it.

This stepped up AC is applied across the anode and the cathode of the piezo element, which starts vibrating sharply according the pitch of the frequency, generating a shrill, ear piercing sound in the air.

However to make the sound audible at maximum intensity, the piezo transducer needs to be stuck or installed in a special way inside its housing.

how to stick piezo


For this particular application the piezo element needs to be stuck at the base of its housing which must consist of a hole having a diameter of about 7 mm. 

The piezo element cannot be stuck directly over the base of the housing, rather it must stuck and positioned over a soft, pure rubber ring, having diameter 30 % less than that of the piezo transducer.
Only if the above fixing procedure is followed, the buzzer will sound, otherwise the sound may get choked and fail to reproduce.

 Parts List for the proposed simple piezo buzzer circuit

R1 = 100K,
R2 = 4k7,
T1 = BC547,
L1 = Buzzer inductor,
PZ1 = Piezo element, 27mm, three terminal
Rubber ring = 22mm

15 comments:

  1. Cool project!
    Where and or how do I get or make the;
    "L1 = Buzzer inductor"?

    ReplyDelete
    Replies
    1. In India you can get them in bulk, I have hundreds of them lying with me, I wish I could give it to you. Not sure from where you can get it in your country.

      Delete
    2. HELLO Anonymous, did you find where to get the buzzer inductors? I would like to know where you got them.

      Delete
  2. Is it available readymade in the nearby local electronic equipment stores?????

    ReplyDelete
  3. Would you be more specific in describing the Buzzer Inductor? What is the value of the inductance? open aired or ferrite cored? a picture is worth a thousand words.Thanks.

    ReplyDelete
    Replies
    1. Please check the image here:

      http://1.bp.blogspot.com/-j-B5fWFwJVo/UQTewNIMC7I/AAAAAAAACzA/Y7WLCNIbUGs/s1600/buzzer%20coil.jpg

      Delete
    2. L value depends on the resonance frequency you would like to generate and the supply voltage. I have used 3V and generating 35V across the coil at 3kHz. I have used a ferrite 10mH inductor. Hope that helps.

      Delete
  4. hi,
    can u provide me the data sheet for the above circuit.?
    tat means, current and voltage levels for each component, etc..

    ReplyDelete
    Replies
    1. why do you need it? it's not necessary for such a simple design

      Delete
    2. i need datasheet because i am planning to use this part in my project.So i need tat.pls help me.
      Thanks.

      Delete
    3. if you Google "27mm piezo datasheet" and "BC547 datasheet" you'll easily find them on the web.

      Delete
    4. Hi Anonymous,
      Though this post is quite old, I saw it today and feel like commenting on it. If you have already solved your problem, then simply skip it.

      First, it would be much better if you create a user name rather than post as "Anonymous".

      Second, I think Swagatam Majumdar has not actually built this circuit, so he may not be able to answer your specific questions regarding the actual current and voltage levels for the components during operation ;-)

      So the best alternative is to build the circuit yourself and measure the voltages and currents at various points. I am sure you are capable of doing that much yourself; why do you want to be spoon fed?

      Regarding the inductor, check above for the post of Kramadhati for clear detailsof of the same. Good luck.

      Delete
    5. For your kind information Mr. Chinmoy, I have built and sold many, many 1000 pieces of this unit, so I think I know about this circuit quite well.

      This is an oscillator design and therefore might not have fixed values at the different points which might vary depending on the specs of the particular piezo, inductor, and also the supply levels, that's the reason why i could not specify the details to Mr. Anonymous

      Delete
    6. the inductor value is 40mH wound over a ferrite drum

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.
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