Elenco Electronics 202 - Manual (Page 126)

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Project #298
OBJECTIVE: To build a circuit that blinks an LED and drives a speaker.
Set the adjustable resistor (RV) to the far left and turn on the slide
switch (S1). The LED (D1) lights and the speaker (SP) sounds once
per second. Adjusting the adjustable resistor to the right increases the
rate.
Blink & Beep
OBJECTIVE: To modify project #298 for a seven second delay and then a
continuous sound.
Project #299
Blink & Beep (II)
Replace the 10 μF capacitor (C3) with the 100μF capacitor (C5) and the
0.02 μF capacitor (C1) with the 0.1μF capacitor (C2). When you turn on
the slide switch (S1), LED (D1) will light every 10 seconds. The
speaker (SP) clicks as the light blinks.
Project #300 Simple Rectifier (II)
OBJECTIVE: To convert a changing voltage into a constant
voltage.
Build the circuit shown but leave the fan off the motor (M1). Turn on the slide
switch (S1); the motor spins and the 6V lamp (L2) and the LED (D1) light. The
LED will not be very bright so turn off the room lights, or hold your fingers
around it to see it better.
Now remove the 470 μF capacitor (C5) from the circuit. The motor spins just as
fast and the lamp is still bright, but the LED is very dim. Why?
The spinning shaft in the motor creates a changing voltage, which can barely
light the LED. The 470
μF capacitor can store electricity, and it combines with
the NPN transistor (Q2) to make a rectifier. This rectifier converts the changing
voltage from the motor into a constant voltage, which makes the LED bright.
Place the capacitor back into the circuit and place the fan on the motor. Now
the motor spins more slowly and the LED is off again, but the 6V lamp is slightly
brighter. The motor has less voltage when it spins slower, so the LED stays off.
But there is more voltage across the lamp now, making it brighter.
The electricity supplied to your home by your electric company is actually a
changing voltage. Many electronic products use rectifier circuits to convert this
into a constant voltage like a battery provides.
!
WARNING:
Moving parts.
Do not touch the
fan or motor
during operation.