Elenco Electronics 202 - Manual (Page 89)

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Project #205
OBJECTIVE: To show how voltage polarity affects a DC motor.
Place the fan onto the motor (M1). Press the press switch (S2), the fan
rotates clockwise. When you connect the positive (+) side of the battery
(B1) to the positive (+) side of the motor, it spins clockwise. Release the
press switch and turn on the slide switch (S1). Now the fan spins the
other way. The positive (+) side of the battery is connected to the
negative (–) side of the motor. The polarity on the motor determines
which way it rotates. Notice that the lamp (L2) lights in both polarities. It
is not effected by the polarity changes.
Motor Rotation
OBJECTIVE: To build a circuit that controls how long the fan is on.
Place the fan onto the motor (M1) and set the adjustable resistor (RV) control to the far
right. Turn the slide switch (S1) on and then press the press switch (S2) once. The motor
will spin and then stop. Now set the resistor control to the far left and press the press switch
again. The time the fan spins is much less now.
When the press switch is pressed, the current flows through the circuit and the fan spins.
The 100
μF capacitor (C4) charges up also. When the switch is released, the capacitor
discharges and supplies the current to keep the transistors (Q1 & Q2) on. The transistor
acts like a switch connecting the fan to the battery (B1). When the capacitor fully
discharges, the transistors turn off and the motor stops. The adjustable resistor controls
how fast the capacitor discharges. The more resistance, the longer the discharge time.
Project #207
Motor Delay Fan (II)
OBJECTIVE: To change capacitance to affect time.
Use the circuit from project #206. Connect a single snap under the positive (+) side of the
470
μF capacitor (C5) and then connect it over the top of the 100μF capacitor (C4). Turn
the switch (S1) on and press the press switch (S2). Notice that the fan spins longer now.
When capacitors are in parallel, the values are added, so now you have 570
μF. The time
it takes to discharge the capacitors is longer now, so the fan keeps spinning.
Project #206 Motor Delay Fan
!
WARNING: Moving parts. Do not touch the fan or
motor during operation.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation.