Elenco Upgrade Kit SC300 to SC750 - Manual (Page 105)

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Project #587
OBJECTIVE: Using AC and DC current.
AC & DC Current
This circuit creates an AC & DC current. Press the press switch (S2)
a few times and the LED’s flash back and forth. Turning the switch on
and off causes the magnetic field in the transformer (T1) to expand
(green LED D2 lights) and collapse (red LED D1 lights) and current
flows in two directions. Hold the switch down and the green LED
flashes once. Replace the 6V lamp (L2) with the motor (M1). Press
the press switch, the red LED flickers and the speaker sounds, due to
the small current change from the motor spinning.
Project #588
OBJECTIVE: To create a sound circuit.
Noisemaker
Turn on the slide switch (S1) and the relay (S3) generates a buzzing
noise. Increase the voltage across the relay by pressing the press
switch (S2). The tone is higher because the relay’s contacts are
opening and closing faster.