Simple Piezo Buzzer Circuit

This project makes sound in a whole new way.

It is surprisingly easy to build and only uses a few parts:

• A transistor like a tiny switch
• A special coil like a mini electromagnet
• A tiny speaker component piezo transducer that turns electricity into vibrations

The result is a high pitched sound, kind of like a whistle.

This circuit is unique because it uses the coil to make the sound keep going unlike most circuits that use resistors and capacitors.

What is a Piezo Buzzer Circuit:

A piezo buzzer circuit is a simple electronic circuit that uses a piezoelectric buzzer to produce sound.

Piezo buzzers are commonly used in electronic devices for generating audible alerts notifications, or alarms.

The key component in a piezo buzzer is the piezoelectric element which vibrates in response to an applied voltage, creating sound waves.

Circuit Description:

Parts List:

Examining the piezo buzzer circuit diagram reveals that the circuits core consists of the transistor T1 and the inductor.

Essentially, the buzzer coil appropriately named is strategically positioned to amplify the generated oscillations while the central tap of the three terminal piezo element used in this application provides crucial feedback.

Upon introducing voltage to the circuit, the transistor conducts activating the piezo element across the buzzer coil.

However, this action simultaneously grounds the transistors base through the central tap of the piezo element promptly turning off the transistor and consequently the piezo.

This releases the transistors base causing it to return to its initial stat thus initiating a cycle that repeats generating the desired oscillations or “buzzing” frequency.

The central tap of the piezo transducer proves pivotal in sustaining the oscillations.

Therefore, for this design a three terminal piezo is essential unlike a two terminal one.

The oscillations produced at the transistors collector are channeled into the coil saturating it with magnetic induction.

The coil then releases stored energy during oscillations amplifying the generated AC across it.

This stepped up AC is applied across the piezo elements anode and cathode prompting it to vibrate sharply according to the frequencys pitch and generating a sharp ear piercing sound.

To maximize sound intensity the piezo transducer must be carefully glued or installed inside its housing.

Achieving the desired frequency involves a design reminiscent of a crystal oscillator where the piezo functions similarly to a ceramic crystal.

The frequency of the oscillator though challenging to derive precisely follows a design resembling a crystal oscillator.

In this specific application the piezo element must be affixed at the base of its housing which should feature a hole with a diameter of approx 7mm.

Formulas:

The resonant frequency of an electrical circuit with a linked inductor L and capacitor C is determined by this formula.

The precise frequency at which a circuit responds to an alternating current AC signal to the greatest extent is known as the resonance frequency.

Frequency = 1 / (2π√L_sC_s)

here,

• f: Represents the resonant frequency, measured in hertz Hz.
• 2π: A mathematical constant pi (approximately 3.14159) multiplied by 2, it serves as a conversion factor in the formula.
• √: Square root symbol.
• L: Represents the inductance of the circuit, measured in henrys H, inductors oppose changes in current.
• C: Represents the capacitance of the circuit, measured in farads F, capacitors store electrical energy.

Calculation Steps:

Measure the inductance L and capacitance C of your circuit electronic devices or component specifications can be used to measure these quantities.

Substitute the measured values of L and C in the formula ensure that the capacitance and inductance are measured in their appropriate standard units F for Farad and H for Henry.

Calculate the square root of the product (L x C).

Divide 1 by (2π x square root of (L x C)) your circuits resonance frequency expressed in hertz Hz will be the outcome.

For example, if your circuit has an inductance L of 1 henry and a capacitance C of 1 farad:

• f = 1 / (2π√(1 x 1))
• f = 0.159 Hz (after calculating the square root and division)

This means the circuit will have a maximum response to an AC signal at a frequency of approximately 0.159 Hz.

How to Build:

Below mentioned are the steps to build a Simple Piezo Buzzer Circuit:

• Position the NPN transistor T1 on the breadboard.
• Connect the ferrite inductor to the collector of the transistor.
• Connect the three terminal piezo transducer to the base and emitter of the transistor.
• Add resistors and capacitors as per the circuit design.
• Use connecting wires to establish the necessary connections between components based on the circuit diagram.
• Connect the power supply to the appropriate points on the breadboard ensuring it matches the required voltage for the circuit.

Piezo Transducer Installation

• Create a housing for the piezo transducer with a hole having a diameter of about 7mm.
• Attach the three terminal piezo element at the base of the housing.
• Affix a soft, pure rubber ring with a diameter 30% less than that of the piezo transducer on top of the piezo.
• Carefully glue or secure the piezo transducer and the rubber ring inside the housing to ensure proper positioning.

Testing and Adjust:

• Turn on the power supply and observe the circuits behavior.
• If the circuit is functioning correctly, you should hear a buzzing sound from the piezo transducer.
• Adjust resistor and capacitor values if necessary to achieve the desired frequency.
• Fine tune the positioning of the piezo transducer inside the housing to maximize sound intensity.

Note:

• By following these detailed steps, you can construct a simple piezo buzzer circuit with inductive feedback generating distinctive oscillations.
• Adjustments can be made to tailor the circuit to specific frequency requirements.

References

BUZZER BASICS -TECHNOLOGIES, TONES,AND DRIVE CIRCUITS

Design Techniques to Increase a Piezo Transducer Buzzer Audio Output