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DAN107
Piezo Elements
By Michael
Simpson
I'm not going to get into
the deep theory of piezo elements mainly cause I don't think you need it to
make use of these little gems. There are several different categories
and types of piezo elements but for the sake of simplicity I will describe a
few as follows.
Raw Piezo element
This type is only the
raw element. They consist of a small piezoceramic plate and
electrode. This type is of element is not much use to us as while it
can make noise, without an acoustical enclosure it wont be that loud.
Encased Piezo element
This is the type of
element that this paper is written for. It's the Raw piezo element but
it is encased in a small enclosure that is designed to resonate at the
operational frequencies of the element.
Encased Piezo buzzer
The last type is the
same as the Encased Piezo element but contains circuitry to generate a tone
so that only power is needed to drive this device. There are two disadvantages
to this type of Piezo.
Have you ever hooked a
piezo element up to a microcontroller and found that the sound it made while
pulsing the pins to be very inadequate? I have. After some
research I found that most piezo elements were to designed to resonate with
the acoustical chamber built into the case.
By varying the frequency
you can find the frequency or frequencies that a piezo was designed to operate.
The piezo that I'm using resonates at both 2.1KHz and 4KHz. This allows
it to be used to generate two tones which give us a bit more flexibility
for getting someone's attention.
Hookup
I made the hookup as
simple as possible and really the only thing you need for this paper is an
Athena and a piezo element.
Schematic 1
This first program is very simple.
It cycles back and forth between the two frequencies.
Program 1
loop:
signal 0,50,7
signal 0,25,20
goto loop
This next program uses the
Athena signal command to generate a series of tones. You can watch the
Athena cycle through the frequencies. Use your ears to hear what the actual
frequencies the Piezo resonates at.
Program 2
download it here
dim period
for period = 1 to 50
print "period=",period
signal 0,100,period
pause 255
next
Try placing a piece of
tape over the hole and running through the frequencies again. Put a
small pin hole in the tape. The tape
changes the resonating frequency. You can do various things to change
the resonating frequency of the cavity. I enlarged the hole to a 1/8"
and changed the main resonating frequency to 2600 Hz.
Parts
Easy RS232 Driver
Athena
Piezo Element
16 Pin Dip Heat
Sink
Easy Motor PCB
6 Cell Battery
Holder
9v Battery Clip
7805
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