-If you are designing products like a home appliance, security panel, a door-entry system or a computer peripheral, you might choose to feature a buzzer as the sole means of interacting with users or as part of a more sophisticated user interface.

-In either case, the buzzer can be an inexpensive and reliable means of acknowledging a command, indicating the status of equipment or a process, prompting interaction, or raising an alarm.

-Fundamentally, a buzzer is usually either amagnetic or piezoelectrictype. Your choice can depend on the characteristics of the drive signal, or the output audio power required and physical space available. You can also choose between indicator and transducer types, depending on the sounds you want and the circuit-design skills available to you.

-Let us take a look at the principles behind the different mechanisms and then consider whether the magnetic or piezo type (and the choice of indicator or actuator) could be right for your project.

-Magnetic buzzers

-Magnetic buzzers are essentially current-driven devices, typically requiring more than 20mA to operate. The applied voltage can be as low as 1.5V or up to about 12V.

-As figure 1 shows, the mechanism comprises a coil and a flexible ferromagnetic disk. When the current is passed through the coil, the disk is attracted towards the coil and returns to its normal position when the current is not flowing.

-This deflection of the disk causes air in the vicinity to move, and this is interpreted as sound by the human ear. The current through the coil is determined by the applied voltage and the coil impedance.