Elenco 130-in-1 Electronics Playground - Manual (Page 79)

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Now you will build an oscillator using two transistors
connected directly to each other. As you have
witnessed, there are many ways to make an
oscillator. This way is easier compared to some.
After finishing the wiring, press the key. You hear a
beep sound coming from the speaker. Now rotate the
control. How does it change the sound?
The two transistors collaborate with each other and
act as a single transistor. The NPN transistor
amplifies the signal from the 22k
Ω resistor and sends
it to the PNP transistor, to obtain a larger output.
The frequency of the oscillation is determined by the
capacitor. The project starts with the 0.01
μF
capacitor in the circuit but you can experiment with
alternate value capacitors. The control alters the
voltage leading to the base of the NPN transistors. It
alters the tonal quality as well as the frequency. You
should be sure to record your results like a
professional scientist, so you can repeat the
experiment later. If you alternate capacitor values, be
sure to observe the polarity (+ and –) of the
electrolytic capacitors.
Notes:
EXPERIMENT #61: DOUBLE-TRANSISTOR OSCILLATOR
Wiring Sequence:
o 1-29
o 2-30
o 3-48-138
o 5-101-44
o 26-45-76
o 27-85
o 28-124-137
o 46-102-86
o 47-43
o 75-119
o 121-122
Schematic
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The “R-C” in this experiment’s name represents
resistance-capacitance. You have seen how varying
resistance and capacitance can affect the pulsing
action of an oscillator. This experiment lets us see
the effects when we can alter the strengths of both
resistors and capacitors.
View the schematic. You can see the switch lets you
choose between two different capacitors. Connecting
terminals 13 and 14 adds another resistor to the
circuit.
Build the circuit and set the switch to position B.
Press the key, and leave terminals 13 and 14
unconnected. What kind of sound comes from the
speaker? Now set the switch to A and press the key
another time. Is there any difference in the sound?
Now attach terminals 13 and 14 and press the key.
Try both settings of the switch with terminals 13 and
14 attached and see what occurs.
Which combination gives you the highest tone? The
lowest? What does this show you about how
capacitors and resistors affect each other? Take
meticulous notes about the effects of the different
value capacitors and resistors.
Notes:
EXPERIMENT #64: ADJUSTABLE R-C OSCILLATOR
Wiring Sequence:
o 1-29
o 2-30
o 3-47-110
o 4-87-89-138
o 5-101-105-109
o 13-88
o 14-90-46-132
o 48-121
o 102-131
o 106-133
o 119-137
Schematic