Elenco Circuit Maker Sound Plus 200 - Manual (Page 30)

-29-
Project #47
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 4.5V lamp (L4) will be bright but there should be
no sound.
Reset the circuit by turning the slide switch (S1) off and back on. 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. You have a reflection detector!
The photoresistor is used as a switch here to turn on music from the
recording IC (U6).
Reflection Detector
Project #48
Let’s modify the reflection detector circuit so that it is not so loud. We’ll
also put a light 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 4.5V lamp (L4) 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 a more faint sound and the LED (D1) should light now as
the mirror reflects light from the lamp onto the photoresistor.
Quiet Reflection Detector
CM-200_Manual_031914.qxp_CM-200_Manual_031914 4/2/14 12:04 PM Page 30