Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 44)

-44-
Now it’s time to make some noise. To do this we need a
speaker. A speaker converts electrical energy into
sound. It does this by using the energy of an AC
electrical signal to create mechanical vibrations. These
vibrations create variations in air pressure, called sound
waves, which travel across the room. You “hear” sound
when your ears feel these air pressure variations. You
need high current and low voltage to operate a speaker,
so we will always use the transformer with the speaker.
(Remember that a transformer converts high-voltage/low-
current to low-voltage/high-current). We create an AC
signal for the speaker using the oscillator circuit
introduced in the last experiment, with minor changes. A
speaker has a schematic symbol like this:
Connect the wires according to the Wiring Checklist.
Notice that transformer springs 23 and 24 are not
connected although their wires cross in the schematic.
Also notice there are 4 resistors and 4 capacitors
connected to the 3.3K
Ω resistor and 2 loose wires
connected to the transformer. Connect the transformer to
one resistor and one capacitor at a time, then press the
switch and listen. All the combinations are listed below,
you don’t need to try all of them but try some and see if
there is a pattern in the frequency or pitch (a term used
in music) of the sound. Record a few comments about
the sound you hear.
You may start to see the same thing we told you about
the blinking LED frequency - that the frequency increases
when you lower the resistance or capacitance. It also
increases if you lower the inductance, but you don’t have
any other inductors you can substitute.
Oscillators are among the most important circuits in
electronics and most of your remaining experiments will
use an oscillator of some form. Although the oscillator
circuits used here are simple ones, some oscillators can
be the most difficult circuits to design.
EXPERIMENT #27: Electronic Sound
Speaker
Symbol for
Speaker
10K
Ω
33K
Ω
100K
Ω
1M
Ω
.0047
μF
.047
μF
10
μF
100
μF