Elenco Snap Circuits SOUND &reg - Manual (Page 79)

Turn on the right slide switch
(S1). Set the lever on the
adjustable resistor (RV) to each
side and compare the sound
with the left slide switch on or off.
With the lever up, RV is a 200 W
resistor. Turning the left switch
off connects this in series with
the 5.1k
W resistor (R3), and
has a small effect on the tone.
With the lever down, RV is a
50k
W resistor. Turning the left
switch off connects this in
series with the 5.1k
W resistor
(R3), and has a big effect on
the tone.
Turn on the right slide switch (S1). Set the
lever on the adjustable resistor (RV) to
each side and compare the sound with the
left slide switch on or off. If there is no
sound when the lever is set all the way up,
adjust it down a little until there is sound.
With the lever up, RV is a 200 W resistor.
Turning the left switch off connects this in
parallel with the 5.1k
W resistor (R3), and
has a big effect on the tone.
With the lever down, RV is a 50k W resistor.
Turning the left switch off connects this in
parallel with the 5.1k
W resistor (R3), and
has a small effect on the tone.
Pressing any of the green keys now will
change the tone, by connecting resistors
inside the keyboard in parallel with your
R3-RV resistor network.
Project 175 Resistors in Series
Project 176 Resistors in Parallel
Think of resistors as
obstructions to the flow of
electricity. When there is only
one path for electricity and
part of it has a big
obstruction, not much will
flow. When there are several
paths for electricity and one
has a big obstruction, a lot
will flow because most will
flow through the
unobstructed path.
Inside the keyboard module (U26) is an
oscillator circuit that produces separate
tones for the blue and green keys. The
frequency (pitch) of the tone is set using
an internal resistor-capacitor network,
with each key representing a different
resistor value. The green keys can be
adjusted using the tune knob.
The tone of the green keys can also be
changed using external resistors and
capacitors, which is done in many of the
projects.
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