page 35
Piezo electricity
is the charge which accumulates in
certain solid materials in response to mechanical pressure,
but also providing the charge to the piezo electric material
causes it to physically deform. One of the most widely
used applications of piezo electricity is the production
of sound generators, called piezo buzzers.
Piezo buzzer
is an electric component that comes in different shapes
and sizes, which can be used to create sound waves
when provided with analog electrical signal. mikromedia
™
workStation v7 comes with piezo buzzer which can be
connected to
G4.2
or
G4.3
microcontroller pin. Connection
is established using
SW3.8
or
SW4.8
DIP switch. Buzzer is
driven by transistor
Q1
(
Figure 25-1
). Microcontrollers can
create sound by generating a PWM (Pulse Width Modulated)
signal – a
square wave
signal, which is nothing more than
a sequence of logic zeros and ones. Frequency
of the square signal determines the pitch of the
generated sound, and duty cycle of the signal can be
used to increase or decrease the volume in the range
from 0% to 100% of the duty cycle. You can generate
PWM signal using hardware capture-compare module,
which is usually available in most microcontrollers, or by
writing a custom software which emulates the desired
signal waveform.
Supported sound frequencies
Piezo buzzer’s resonant frequency (where you can expect
it's best performance) is
3.8kHz
, but you can also use it
to create sound in the range between
2kHz
and
4kHz
.
SW3
R17
10K
Q1
BC846
R16
1K
VCC-5V
PZ1
BUZZER
1
2
3
4
5
6
7
8
O
N
SW4
BUZZER
G4.3
1
2
3
4
5
6
7
8
O
N
BUZZER
G4.2
PERSPECTIVE
VIEW
TOP
VIEW
DATA BUS
In order to use the on-board Piezo Buzzer in your
application, you first have to connect the transistor
driver of piezo buzzer to the appropriate pin. This
is done using
SW3.8
or
SW4.8
DIP switch (never in
the same time). Once the switch is in ON position,
it connects the buzzer driver to
G4.2
or
G4.3
pin.
Buzzer starts "singing" when you provide
PWM signal from the microcontroller
to the buzzer driver. The pitch of the
sound is determined by the frequency,
and amplitude is determined by the
duty cycle of the PWM signal.
Enabling Piezo Buzzer
How to make it sing?
Figure 15-1: Piezo
buzzer connected to
G4.3 microcontroller pin
Freq = 3kHz, Duty Cycle = 50
%
Freq = 3kHz,
Volume = 50
%
Freq = 3kHz,
Volume = 80
%
Freq = 3kHz,
Volume = 20
%
Freq = 3kHz, Duty Cycle = 80
%
Freq = 3kHz, Duty Cycle = 20
%
TO SOCK
ETS
VCC-5V
R3
1K
PZ1
Q8
BC846
10K
R27
PERSPECTIVE
VIEW
TOP
VIEW
RE1
RC2
J21
BUZZER
TO SOCK
ETS
VCC-5V
R3
1K
PZ1
Q8
BC846
10K
R27
PERSPECTIVE
VIEW
TOP
VIEW
RE1
RC2
J21
BUZZER
TO SOCK
ETS
VCC-5V
R3
1K
PZ1
Q8
BC846
10K
R27
PERSPECTIVE
VIEW
TOP
VIEW
RE1
RC2
J21
BUZZER
Piezo Buzzer
other modules
