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PICAXE-08 ALARM PROJECT
revolution
© copyright 2002 - AXE102 Alarm Student Project Notes Version 1.1
Revolution Education Ltd. Email: [email protected] Web: www.rev-ed.co.uk
11
Supported by:
B
UZZERS
AND
P
IEZO
-T
RANSDUCERS
What is a piezo transducer?
A piezo transducer is a low-cost 'mini-speaker' that can used to
make sounds. The sound that the piezo makes can be changed
by altering the electronic signals provided by the
microcontroller.
Where are piezos used for?
Piezos are used in many different consumer goods to provide 'feedback' to the user. A
good example is a vending machine which will 'beep' whenever a keypad switch is
pressed to select a drink or snack. The 'beep' provides the user with feedback to tell them
their switch push has been successful. Uncased piezos are also often used in musical
birthday cards to play a tune when the card is opened.
What is the difference between a piezo and a buzzer?
A buzzer contains a small electronic circuit that generates the electronic signal needed to
make a noise. Therefore when a buzzer is connected to a battery it will
always make the same sound. A piezo does not contain this circuit, and so
therefore needs an external signal. This signal can be supplied by the
output pin of a microcontroller. A piezo also requires less current to
operate and so will last longer in battery powered circuits.
Using piezos.
A piezo is very simple to connect. Simply
connect the red wire to the microcontroller
output pin and the black wire to 0V
(ground).
Note that the cheapest piezos do not have a
plastic casing to them. In this case it is
necessary to mount the piezo on a piece of
board (with a sticky pad) to create a noise
that can be heard. The board acts as a
'sound-box' to amplify the sound made by
the piezo. Make sure the sticky pad is stuck
on the correct side of the piezo (the brass side
without the wires!).
Making More Noise.
Some times you might want to make a louder noise. In this case it is
possible to use a speaker instead of the piezo. When using a speaker
it is also necessary to use a capacitor (e.g. 10uF electrolytic capacitor)
to prevent damage to the microcontroller.
Remember that, like the piezo, a speaker only works correctly when
mounted in a 'sound-box'.
pin
0V
pin
0V
+
40R
10uF
