Elenco 130-in-1 Electronics Playground - Manual (Page 19)

-142- -19-
Did you know that many marine animals
communicate to each other using sound? I bet you
have heard that dolphins and whales use sound for
communication, but what you probably don’t know is
that they are not the only ones. Due to research we
are able to find out that some fish are attracted to
certain sounds. Making this circuit, will allow you do
to some research of your own.
Once you make the last connection you are turning
on the power. You should be able to hear pulses of
sound coming from the speaker. The sound changes
by turning the control. This circuit is a type of audio
oscillator circuit, which you will learn more about later
in this book.
If you have a fish tank at home or at school you
should place your kit near the glass to see if the fish
are attracted to the sound. Are they?
If you like to fish, you should try this out while fishing.
What you need to do is attach another speaker to
terminals 1 and 2 using long lengths of insulated
wire. Wrap the speaker carefully in a waterproof
plastic bag or place it in a tightly sealed jar. Make
sure that no water is able to reach the speaker. Lower
the speaker into the water, cast your fishing line, and
see if you catch anything.
Notes:
EXPERIMENT #8: CALLIN’ FISH
Wiring Sequence:
o 1-29
o 2-30
o 3-93-100-110
o 4-120
o 5-41-109
o 27-94
o 28-40-99
o 42-119
Schematic
When you connect the signal from this oscillator to
an oscilloscope, it creates a pattern that looks like
the teeth of a saw (as shown below).
The shape of this wave results from the slow
charging of the 0.1
μF capacitor through the control
and the 100k
Ω resistor, and the capacitor’s
discharge through the PNP and NPN transistors.
The voltage divider - the 470
Ω and 100Ω resistors -
provides about 1.6 volts to the transistors. Current
flowing from the 9V supply into the 0.1
μF capacitor
(through the control and the 100k
Ω resistor) slowly
charges up the capacitor. When the capacitor’s
charge exceeds the voltage of the voltage divider
(1.6V), the transistors turn on and provide a path for
the 0.1
μF capacitor to discharge quickly. Now, the
transistors turn off again, and the capacitor begins
to slowly charge to repeat the cycle.
You can modify the oscillator frequency by changing
the values of the components in the timer circuit - the
control, the 100k
Ω resistor and the 0.1μF capacitor.
Try a 47k
Ω resistor or a 220kΩ resistor in place of
the 100k
Ω resistor, and try several different
capacitors. If you connect one of the electrolytic
capacitors, be sure that you use the proper polarity
(+ and –).
Notes:
EXPERIMENT #120: SAWTOOTH OSCILLATOR
Schematic
Wiring Sequence:
o 73-81-27-119
o 28-89
o 71-74-47-40
o 41-46
o 42-43-90-109
o 124-44-48-110-72-EARPHONE
o 45-82-EARPHONE
o 121-122