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Project #381
OBJECTIVE: To construct a time delay circuit.
Turn on the slide switch (S1) and the bulb (L2) does not light. Press
switch (S2) and slowly the bulb lights.
When the switch (S2) is pressed, current flows to the base of the
transistor (Q2) and charges the 100µF capacitor (C4). When the
capacitor charges up to more than 1 volt, the transistor (Q2) turns on
and triggers the SCR (Q3). The bulb will stay lit until the slide switch
(S1) is turned on. The values R5 and C5 determine the time it takes
until the transistor turns on. The larger the capacitor value, the more
time it takes to turn on.
Delay Light
Project #382 Project #383
OBJECTIVE: To construct a time delay fan.
Delay Fan
OBJECTIVE: To construct another type of time delay fan.
Delay Fan (II)
Use the circuit in project 381. Replace the bulb (L2) with the motor (M1)
and fan. Turn on switch (S1) and press down switch (S2) to start the
motor.
Use the circuit in project 381. Replace the 100µF capacitor (C4) with
the 470µF capacitor (C5). Turn on switch (S1) and press switch (S2).
See how long it takes until the motor (M1) spins.
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