Elenco Electronics 202 - Manual (Page 60)

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Project #115 Sucking Fan
OBJECTIVE: To adjust the speed of a fan.
Project #117 PNP Collector
OBJECTIVE: To
demonstrate adjusting the
gain of a transistor circuit.
OBJECTIVE: To build a fan that
won’t come off.
Modify the circuit from project #115 by
reversing the position of the motor
(M1) so the positive (+) side is
towards the PNP transistor (Q1). Turn
it on, and set the adjustable resistor
(RV) for the fan speed you like best.
Set it for full speed and see if the fan
flies off - it won’t! The fan is blowing
air upward now! Try holding a piece of
paper just above the fan to prove this.
Project #116
Blowing Fan
Project #118 PNP Emitter
OBJECTIVE: To compare
transistor circuits.
Compare this circuit to that in
project #117. The maximum
lamp (L2) brightness is less
here because the lamp
resistance reduces the emitter-
base current, which contacts
the emitter-collector current (as
per project #117). The point on
the PNP transistor (Q1) that the
lamp is now connected to (grid
point C3) is called the emitter.
Build the circuit, and be sure to orient the motor (M1)
with the positive (+) side down as shown. Turn it on,
and set the adjustable resistor (RV) for the fan speed
you like best. If you set the speed too fast, then the fan
may fly off the motor. Due to the shape of the fan
blades and the direction the motor spins, air is sucked
into the fan and towards the motor. Try holding a piece
of paper just above the fan to prove this. If this suction
is strong enough then it can lift the fan blades, just like
in a helicopter.
The fan will not move on most settings of the resistor,
because the resistance is too high to overcome friction
in the motor. If the fan does not move at any resistor
setting, then replace your batteries.
Build the circuit and vary the
lamp (L2) brightness with the
adjustable resistor (RV), it will
be off for most of the resistor’s
range. The point on the PNP
transistor (Q1) that the lamp is
connected to (point E3 on the
base grid) is called the
collector, hence the name for
this project.
!
WARNING: Moving parts. Do not
touch the fan or motor during operation.
!
WARNING: Do not
lean over the motor.
!
WARNING: Moving parts. Do not
touch the fan or motor during operation.