Piezo buzzer is the handy sound generator used in electronic circuits to give audio indication .It is widely used as alarm generator in electronic devices. It is available in various types and size to suit the requirements. A Piezo buzzer has a Piezo disc and an oscillator inside. When the buzzer is powered, the oscillator generates a frequency around 2-4 kHz and the Piezo element vibrates accordingly to produce the sound. An ordinary Piezo buzzer works between 3 – 12 volts DC.
Working of the Piezo element
Piezo element is a circular shaped metal plate with a thin coating of Piezo material. The piezomaterial used is Lead Zirconate Titanate. This material exhibits both Direct and Indirect piezoelectric property. Indirect piezoelectric property is the vibration of the piezoelectric crystals in the presence of an electric field. The piezoelectric crystals also show direct piezoelectric property in which a mechanical stress like vibration or application of heat generates around 1-2 volts in the Piezoelement. The white Piezo material coating is Positive while the rim of the element is Negative.
Oscillator circuit inside the buzzer consists of an Inductor, a transistor, capacitors and resistors. When the oscillator circuit gets 3-12 volt DC, The transistor, Inductor combination oscillates which are fed to the Piezo crystals and the crystals and the plate vibrate according to the frequency. In order to give resonance, the rim of the element is glued to a plastic case so that the plate can vibrate freely.
Why Piezo buzzer generates piercing sound?
The oscillation in the Piezo buzzer is between 2 – 4 kHz. This sound is piercing because our hearing threshold is maximum in this frequency. Buzzer uses this frequency to get easy attention even in a highly noisy environment. Buzzers are used as alarms so this frequency is necessary.
How to handle Piezo element?
Piezo element is prone to weather changes and aging. The piezoelectric property may deteriorate due to aging and the buzzer may fail to work. The Piezomaterial is coated as a thin film so that during soldering, the wire along with the piezomaterial may detach. Once a portion of the Piezo material is detached, that element cannot be used. So always use very thin wire and apply solder only once. Over heating may damage the piezomaterial. If it is stored, use a plastic cover and keep it in a place free from moisture and heat.
Direct Piezoelectric Effect
Mechanical vibration can generate electricity in Piezo element. Connect a high bright transparent LED directly on the Piezoelement with correct polarity. Gently tap in the central white part of Piezoelement. LED will blink.
See the video nos. 9 and 15 in this link to see the LED lighting