Simple Buzzer Circuit – Piezo Electric Buzzer Explained


In this article we learn how to make a very simple buzzer using using piezo electric transducer and 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