Elenco Circuit Maker Skill Builder 125 - Manual (Page 52)

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Project #103 Long Gone Light
Project #104 Slow Siren Changer
!
WARNING: Moving parts. Do not touch the fan or
motor during operation.
! WARNING: Do not lean over the motor.
This circuit demonstrates how
capacitors store up energy when
S2 is pressed, and then discharge
energy when S2 is released.
Push the press switch (S2). If the fan is off the motor (M1) (or flies off)
then the LED (D1) will be bright.
It takes a lot of current to spin the motor when the fan is on it, and the
voltage drops because the batteries (B1) cannot supply enough. When
the fan flies off, the current drops and the voltage rises. The NPN
transistor (Q2, used here as a diode) and 470mF capacitor (C5) are a
detector circuit, which measures the voltage at the motor.
Turn on the slide switch (S1) and you hear a siren sound.
Now hold down the press switch (S2) until the sound becomes a fire
engine sound. This delay is due to the 470mF capacitor (C5) charging
up and is controlled by the photoresistor (RP). If there is bright light on
the photoresistor, then the delay will be only a few seconds.
Release the press switch and after a while the sound will be a siren
again. The capacitor slowly discharges through the NPN transistor (Q2).
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:20 PM Page 52