Elenco 130-in-1 Electronics Playground - Manual (Page 78)

-78-
This experiment is an oscillator that is controlled in
an abnormal way: with a pencil mark! You have
caught a glimpse in other oscillator projects how
changing the circuit’s resistance can change the
sound that is produced. Resistors, such as the ones
in your kit, are made of a form of carbon, and so are
pencils (we still call them “lead” pencils, even though
they are now made with carbon, not lead). By
causing the current to flow through different amounts
of pencil lead, we can vary the resistance and
consequently, the tone of the sound coming from the
speaker.
Make a very heavy pencil mark on a sheet of paper
(a sharp #2 pencil works best) once you complete
the wiring. The mark needs to be approximately half
inch wide and 5 inches long.
Set the switch to position A to turn on the power, and
hold one of the probe wires on one end of the mark.
Move the other probe back and forth from one end
of the mark to the other end of the mark. As you
move the probe you’ll hear the pitch rise and fall.
After a little practice you should be able to play a tune
with this organ.
Notes:
EXPERIMENT #60: ODE TO THE PENCIL LEAD ORGAN
Wiring Sequence:
o 1-29
o 2-30
o 3-105-109
o 4-80-131
o 5-47-110
o 92-48-120
o 119-132
o 46-106-91-PROBES
o 79-PROBES
Schematic
-83-
Did you know that a transistor alters its
characteristics according to the temperature? This
experiment will show you how temperature affects
transistor action.
View the schematic. The NPN transistor acts as a
pulse oscillator. The 22k
Ω resistor and the PNP
transistor control the voltage applied to its base. The
transistor’s base current and collector current vary
with the temperature.
Build this experiment and you will hear a sound from
the speaker. Modify the 50k
Ω control so that the
sound is low or a series of pulses.
Hold the PNP transistor between your fingers to
warm it up. As the transistor temperature increases
you will hear the tone become higher.
Notes:
EXPERIMENT #65: HEAT-SENSITIVE OSCILLATOR
Schematic
Wiring Sequence:
o 1-29
o 2-30
o 3-101-103
o 4-26-41-119
o 5-47-104
o 27-81
o 120-28-48
o 40-82
o 42-85
o 46-102-86