Project 43
Fuse
Project 44
Pretend the 3-snap wire marked fuse in the
drawing on the left is a device that will open the
circuit if too much current is taken from the battery.
When you close the slide switch (S1), current
flows from the batteries through the slide switch
(S1), the lamp (L1), motor (M1), and back to the
battery (B1). When press switch (S2) is closed,
the light is shorted and motor speed increases due
to an increase in current to the motor. While still
holding press switch (S2) down, remove the 3-
snap wire marked fuse and notice how everything
stops. Until the fuse is replaced, the open circuit
path protects the electronic parts. If fuses did not
exist, many parts could get hot and even start
fires. Replace the 3-snap wire and the circuit
should return to normal.
Many electronic products in
your home have a fuse that will
open when too much current is
drawn. Can you name some?
-24-
Photo LED Control
Build the circuit shown on the left. Cover the phototransistor
(Q4) and turn on the switch (S1); the color LED (D8) should be
changing colors.
Now shine a bright light on the phototransistor and the color
LED should get dim or turn off. Vary the amount of light on the
phototransistor and see how bright the color LED is. Try using
a flashlight in a dimly lit room.
!
WARNING:
Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.
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