Elenco Electronics 202 - Manual (Page 57)

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Project #108
OBJECTIVE: To show how resistor values change the frequency
of an oscillator.
Turn on the slide switch (S1), the speaker (SP) will sound and the LED
(D1) will light. Adjust the adjustable resistor (RV) to make different
tones. In an oscillator circuit, changing the values of resistors or
capacitors can vary the output tone or pitch.
Adjustable Tone
Generator
OBJECTIVE: To show how resistor values change the frequency
of an oscillator.
Project #110
Electronic Cicada
OBJECTIVE: To show how capacitors in parallel change the
frequency of an oscillator.
Use the circuit from project #108 shown above, replace the
photoresistor (RP) back to the 10k
Ω resistor (R4). Place the 0.1μF
capacitor (C2) on top of the 0.02 μF capacitor (C1) . Turn the slide switch
(S1) on and adjust the adjustable resistor (RV). The circuit produces the
sound of the cicada insect. By placing the 0.1
μF capacitor on top of the
0.02 μF capacitor, the circuit oscillates at a lower frequency. Notice that
the LED (D1) flashes also at the same frequency.
It is possible to pick resistors and capacitors that will make the pitch
higher than humans can hear. Many animals, however, can hear these
tones. For example, a parakeet can hear tones up to 50,000 cycles per
second, but a human can only hear to 20,000.
Use the circuit from project #108 shown above. Replace the 10k Ω (R4)
with the photoresistor (RP). Turn on the slide switch (S1). The speaker
(SP) will sound and the LED (D1) will light. Move your hand up and
down over the photoresistor (RP) and the frequency changes.
Decreasing the light on the photoresistor increases the resistance and
causes the circuit to oscillate at a lower frequency. Notice that the LED
flashes also at the same frequency as the sound.
By using your finger, see if you can vary the sounds enough to make this
circuit sound like an organ playing.
Project #109
Photosensitive
Electronic Organ