Elenco Electronics 202 - Manual (Page 55)

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Project #102
OBJECTIVE: To show how light is used to control a street lamp.
Press the press switch (S2) on and set the adjustable resistor (RV) so
the lamp (L2) just lights. Slowly cover the photoresistor (RP) and the
lamp brightens. If you place more light at the photoresistor the light
dims.
This is an automatic street lamp that you can turn on by a certain
darkness and turn off by a certain brightness. This type of circuit is
installed on many outside lights and forces them to turn off and save
electricity. They also come on when needed for safety.
Automatic
Street Lamp
Project 105
Pitch (III)
OBJECTIVE:
See project #103.
Project #103 Pitch
OBJECTIVE: To show how
to change the pitch of a
sound.
Project 104
Pitch (II)
OBJECTIVE:
See project #103.
Replace the 0.1 μF capacitor (C2)
with the 0.02 μF capacitor (C1)
and replace the 100k Ω resistor
(R5) with the photoresistor (RP).
Wave your hand up and down
over the photoresistor to change
the sound. Changing the light on
the photoresistor changes the
circuit resistance just like varying
the adjustable resistance does.
Note: If you have the adjustable
resistor (RV) set to the right and
light shining on the photoresistor,
then you may not get any sound
because the total resistance is too
low for the circuit to operate.
Build the circuit on the left, turn
it on, and vary the adjustable
resistor (RV). The
frequency or
pitch of the sound is changed.
Pitch is the musical profession’s
word for frequency. If you’ve
had music lessons, you may
remember the music scale
using chords such as A3, F5,
and D2 to express the
pitch of a
sound. Electronics prefers the
term
frequency, as in when you
adjust the frequency on your
radio.
Since we’ve seen we can
adjust the frequency by
varying the resistance in the
adjustable resistor (RV), are
there other ways to change
frequency? You can also
change frequency by
changing the capacitance of
the circuit. Replace the
0.02
μF capacitor (C1) with
the 0.1 μF capacitor (C2);
notice how the sound has
changed.