Elenco Snap Circuits® Deluxe Sound & Light Combo - Manual (Page 136)

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Project 308 Dark Voice Echo
Project 309
Project 310
Dark Echo
Variants
Use either of the preceding two
circuits, but replace the microphone
(X1) with the press switch (S2) or
500kW adjustable resistor (RV3). Press
S2 or turn the knob on RV3 to change
the sound or light.
Modify the preceding circuit to match this
one; it uses the color LED (D8) instead of
the speaker (SP2). Turn on the slide switch
(S1); nothing will happen unless the room is
dark. This circuit only works if there is no
light on the photoresistor (RP).
Cover the photoresistor, talk into the
microphone, and see the light flash. You can
adjust the amount of echo using the lever
on the adjustable resistor (RV). Shine light
on the photoresistor to shut off the circuit.
If the color LED never turns off, then you
need to block light from the photoresistor
better.
Build the circuit as shown, and place it in
a quiet room. Connect the speaker (SP2)
using the red & black jumper wires, then
hold it away from the microphone (X1).
Turn on the slide switch (S1); nothing will
happen unless the room is dark. This
circuit only works if there is no light on the
photoresistor (RP).
Cover the photoresistor, talk into the
microphone, and listen the echo on the
speaker. You can adjust the amount of
echo using the lever on the adjustable
resistor (RV). Shine light on the
photoresistor to shut off the circuit.
If the speaker makes a whining sound that does
not stop, then you need to block light from the
photoresistor better, or the room is too noisy.
The photoresistor controls power to the
echo IC (U28), and acts as an on/off switch.
If the photoresistor is not dark enough, it
may only partially turn on the echo IC,
causing the echo IC to malfunction.
Also, you must hold the speaker away from
the microphone or the circuit may self-
oscillate due to feedback. You also need a
quiet room, with low background noise.
Dark Echo Light
SCC-350_Manual_Part_C.qxp 7/25/14 2:11 PM Page 24