TESTING PIEZO DIAPHRAGMS and PIEZO BUZZERS

There are two types of piezo devices that produce a sound.
They are called PIEZO DIAPHRAGMS and PIEZO BUZZERS.
A piezo diaphragm consists of two metal plates with a ceramic material between. The
ceramic expands and contracts when an alternating voltage is placed on the two plates
and this causes the main plate to "dish" and "bow."
This creates a high-pitched sound. There are no other components inside the case and
it requires an AC voltage of the appropriate frequency to produce a sound.
A piezo buzzer has a transistor and coil enclosed and when supplied with a DC
voltage, the buzzer produces a sound.
Both devices can look exactly the same and the only way to tell them apart is by
connecting a 9v battery. One device may have "+' and "-" on the case to indicate it is
a piezo buzzer, but supplying 9v will make the buzzer produce a sound while the piezo
diaphragm will only produce a "click."

A piezo diaphragm will produce a click

when connected to 9v DC.

A piezo buzzer will produce a tone when

connected to a DC voltage.