The term transducer is used here to describe a noise-creating device that is driven by external electronics. By comparison, an audio indicator (discussed in the next entry) contains its own internal electronics and nly requires a DC power supply. Either of these components is often described as a beeper or buzzer.
A speaker, more properly termed a loudspeaker, is an electromagnetic transducer but
is seldom described in those terms. It has a separate entry in this encyclopedia and is
defined here as a sound reproduction device that is larger and more powerful than a typical transducer and has a more linear frequency response.
While piezoelectric transducers formerly used crystals, only the more modern piezoelectric type that uses a ceramic wafer will be considered here.
Some transducers convert sound into electricity, but these are categorized as sensors,
and will be discussed in Volume 3. The only transducers discussed in this entry are those that convert electricity into sound.
What It Does
An audio transducer is a device that can create an alert. It requires an AC signal that is supplied by external electronics, and in its simplest form may be referred to as a buzzer or a beeper.
Audio alerts are used in microwave ovens, washer/ dryers, automobiles, gasoline pumps, security devices, toys, phones, and many other consumer products. They are often used in conjunction with touch pads, to provide audio confirmation that a tactile switch has been pressed.
The schematic symbols in can be used to represent any kind of audio alert, including indicators, which contain their own electronics to generate a simple tone or series of tones. Type A is probably the most popular symbol.
Types B and C often appear with the word “buzzer” printed beside them for clarification. D and E are really symbols for a speaker, but are often used for an alert. F is the symbol for a crystal, now sometimes used to indicate a piezoelectric noise maker. G specifically represents an electromagnetic transducer, but is seldom used.
How It Works
A circular diaphragm is glued at its edges inside a cylindrical plastic enclosure, usually measuring from around 0.5” to 1.5” in diameter. The enclosure is sealed at the bottom but has an opening at the top, so that sound can emerge from the upper side of the diaphragm without being par- 249 sound source > audio alert > transducer
transducer 27 tially cancelled by sound of opposite phase that is emitted from the underside of the diaphragm.
The enclosure also amplifies the sound by resonating with it, in the same way that the body of a guitar or violin amplifies a note being played on the strings.
. An assortment of symbols which can represent a transducer or an indicator. See text for details.
The diaphragm is activated either electromagnetically or piezoelectrically, as described next.
Externally, a transducer may be indistinguishable from an audio indicator such as the one picturedat