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27
Project #54
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 #55
Photosensitive
Electronic Organ
OBJECTIVE: To show how resistor values change the
frequency of an oscillator.
Project #56
Electronic Cicada
OBJECTIVE: To show how capacitors in parallel change
the frequency of an oscillator.
Use the circuit from project #54 shown above. Replace the
10kΩ resistor (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 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 ashes also at the same
frequency as the sound.
By using your nger, see if you can vary the sounds enough to
make this circuit sound like an organ playing.
Use the circuit from project #54 shown above, replace the
photoresistor (RP) back to the 10kΩ resistor (R4). Place the
0.02μF capacitor (C1) on top of the whistle chip (WC). Place the
slide switch (S1) on and adjust the adjustable resistor (RV). The
circuit produces the sound of the cicada insect. By placing the
0.02μF capacitor on top of the whistle chip, the circuit oscillates
at a lower frequency. Notice that the LED (D1) ashes 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.
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