Elenco Upgrade Kit SC300 to SC750 - Manual (Page 44)

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The length of time the motor (M1) runs depends on the position of the
adjustable resistor (RV). When the press switch (S2) is pressed, the
470
μ F capacitor (C5) charges. As the press switch is released, C5
discharges through the resistors R4 and RV, turning the transistor (Q2)
on. Transistor Q2 connects the relay (S3) to the batteries, the contacts
switch, and the motor (M1) spins. As the voltage decreases, Q2 will turn
off and the motor will stop spinning.
Setting RV to the right (large resistance) sets a long discharge time. To
the left, a short discharge time.
Turn on the switch (S1), the red LED (D1) lights. Now press and release
the switch (S2), the bulb lights and the motor spins.
Project #431
Time Delay
1-7 Seconds
OBJECTIVE: To build a time delay circuit.
Project #432
Time Delay
OBJECTIVE: To see how the capacitor value affects the time.
Use the circuit in project #431. Replace the 470 μ F capacitor (C5) with
the 100 μ F capacitor (C4). Set the adjustable resistor (RV) to the far right,
turn on the switch (S1), then press and release the switch (S2). The
motor (M1) spins and bulb (L2) lights for about 3 seconds. Adjust the
adjustable resistor to the left for a much shorter time.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.