Elenco Circuit Maker Skill Builder 125 - Manual (Page 40)

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Project #73 Little to Big
Project #74
Luminate & Rotate
Project #75
Light to Light
!
WARNING:
Moving parts. Do not
touch the fan or motor
during operation.
!
WARNING:
Moving parts. Do not
touch the fan or motor
during operation.
Transistors, such as the NPN transistor (Q2), can amplify
electric currents. In this circuit, the small current through the
resistor is used to control a larger current through the motor. A
large resistor value limits the current through the lamp, making
it very dim, but the transistor amplified current is large enough
to still spin the motor.
Place the fan on the motor (M1) and turn on the slide switch (S1), then
compare this circuit to Project #31. Push the press switch (S2), the lamp
doesn’t light now but the motor still spins.
The lamp is dark because the 100W resistor (R1) limits the current through it.
The NPN transistor (Q2) uses the small lamp current to create a large current
that spins the motor.
Now replace the 100W resistor (R1) with the larger 1KW resistor (R2). The
motor spins more slowly now, because the transistor cannot create as large of
a motor current from such a small controlling current.
Compare this circuit to Project #73. It uses
the photoresistor (RP) to control the current
to the NPN transistor (Q2), instead of the
press switch (S2). You can adjust the speed
of the motor (M1) by changing how much
light shines on the photoresistor.
The lamp is dark because the photoresistor
limits the current through it. The NPN
transistor uses the small lamp current to
create a large current that spins the motor.
If you tried to control the motor speed by
placing the photoresistor in series with the
motor, the motor would not spin because
the photoresistor would limit the current.
But the photoresistor can control the motor
speed with help from the transistor. You
may need to shine a light on the
photoresistor (RP) if the motor does not
spin.
Compare this circuit to Project #32. Push the
press switch (S2), the motor (M1) doesn’t
spin now but the lamp (L1) still lights.
The motor doesn’t spin because the 100W
resistor (R1) limits the current through it.
The NPN transistor (Q2) uses the small
motor current to create a large current that
lights the lamp.
Now replace the 100W resistor (R1) with
the larger 1KW resistor (R2). The lamp is
only slightly less bright even though the
motor current is much lower.
Now place the 100W resistor back in the
circuit and replace the press switch with
the photoresistor (RP). A bright light on the
photoresistor will turn the lamp on. But if
the light is dim, then the photoresistor has
high resistance, so little current flows
through the transistor and the lamp is off.
WARNING: Moving parts. Do not touch the fan or motor during
operation. Do not lean over the motor.
WARNING: Fan may not rise until switch is released.
!
!
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:19 PM Page 40