Manual

-78-
T
his 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
c
hanging 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.
N
otes:
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
EP-130_62315RevC.qxp_EP-130_062812 6/23/15 11:17 AM Page 78