Project 46
Wave & Watch
People that are deaf need lights to tell them
when a doorbell is ringing. They also use
circuits like this to tell them if an alarm has
been triggered or an oven is ready.
Can you think of other uses?
This circuit does not use the noisy speaker (SP2) but instead uses
a nice quiet color LED (D8). Turn on the slide switch (S1), the LED
flickers. Wait a few seconds, and then cover the phototransistor
(Q4), and the flicker stops. The flicker is controlled by the
photoresistor; uncover it and the flicker resumes.
Project 47
Reflection Detector
Build the circuit to the right. Place it where there won’t
be any room light hitting the phototransistor (Q4) (such
as in a dark room or under a table), and then turn it on.
The 2.5V lamp (L1) will be bright, and one song may
play, but then there should be no sound.
Take a small mirror and hold it over the lamp and
photoresistor. You should hear sound now. You have a
music reflection detector! You can also use a white
piece of paper instead of a mirror, since white surfaces
reflect light.
Note: the motor (M1) will not spin. It is used here to
block light from going directly from the lamp to the
phototransistor.
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