Elenco Projects 1-101 - Manual (Page 27)

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Project #51
OBJECTIVE: To detect if a mirror is present.
Build the circuit at left. Place it where there won’t be any room light
hitting the photoresistor (RP) (such as in a dark room or under a table),
and then turn it on. The 2.5V lamp (L1) will be bright, but 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 reflection detector! You can also
use a white piece of paper instead of a mirror, since white surfaces
reflect light.
Reflection Detector
Project #52
OBJECTIVE: To detect a mirror.
Build the circuit at left. Place it where there won’t be any room light
hitting the photoresistor (RP) (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 reflection detector! You can also
use a white piece of paper instead of a mirror, since white surfaces
reflect light.
Quieter Reflection Detector