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22
Build the circuit as shown. Place the clear cable holder on the red LED (D1)
and the black cable holder on the phototransistor (Q4), then place the ber
optic cable into the holders as far as it will go. For best performance the
cable should stand straight up in the holders, without bending them.
Turn on slide switch (S1) and move the lever on the adjustable resistor (RV)
around. The sound from the speaker (SP) changes as you move the lever
on RV.
Project 19 Blinking Colors
Build the circuit as shown and turn on the slide switch (S1). The white and
color LEDs (D6 & D8) are blinking.
Push the press switch (S2). Now the red LED (D1) is blinking but the white
LED is much dimmer or off.
If you swap the locations of the red and white LEDs, then the red LED will
be blinking and the white LED will be off, and pushing the press switch may
dimly light the white LED but the red LED will hardly be affected.
Red light is easier for LEDs to produce than
white light. When the red and white LEDs are
connected in parallel (which happens when
S2 is pressed), the red LED will dominate
because it turns on more easily.
Fiber Optics
Project 20
Black
Clear
This project is more exciting than it looks. The tone sounds
produced by the strobe IC (U23) are played on the speaker (SP),
even though there is no electrical connection between them.
The left half the circuit makes a coded light signal, which you see
in the red LED (D1). The right half of the circuit decodes the light
signal and plays it on the speaker. The ber optic cable is used
to transmit the light signal between the two sides of the circuit.
There is no electrical connection between the left and right halves
of the circuit, only a light connection using ber optics! If your ber
optic cable was longer, the two halves of the circuit could be many
miles apart.
This circuit is an example of using ber optic cables for
communication. Fiber optics allows information to be transmitted
across great distances at very high speeds with very low
distortion, by using light.
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