Elenco Electronics 202 - Manual (Page 34)

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Project #51
OBJECTIVE: To detect if a mirror is present.
Build the circuit on the 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 6V lamp (L2) will be bright but there
should be little or no sound.
Take a small mirror and hold it over the lamp and photoresistor. You
should hear sound now. You have a reflection detector! The more light
that gets reflected like this, the louder the sound. You can try holding
the mirror at different angles and distances and see how the sound
changes. You can also hold a white piece of paper over them, since
white surfaces reflect light.
Reflection Detector
Project #52
OBJECTIVE: To detect a mirror.
Let’s modify the reflection detector circuit so that it is not so loud and
annoying. We’ll also put a lamp on it that can be seen in a noisy room.
Build the circuit on the left. Place it somewhere 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 6V lamp (L2) will be bright
but there should be little or no sound.
Take a small mirror and hold it over the lamp and photoresistor. You
should hear sound now as the mirror reflects light from the lamp onto
the photoresistor. The more light that gets reflected like this, the louder
the sound. You can also hold a white piece of paper over the circuit,
since white surfaces reflect light.
Quieter Reflection Detector