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Project #284
Mail Notifying Electronic Bell
OBJECTIVE: To build a
circuit to indicate if you have
OBJECTIVE: To build a
Use the circuit from Project 286.
Replace the speaker with a red LED
(the + sign on top). Now you see the
frequency of the oscillator. Install
different values of capacitors to change
the frequency.
Project #287
Quick Flicking LED
OBJECTIVE: To build a circuit
to indicate if you have mail by
Project #286
Twice-Amplified Oscillator
OBJECTIVE: To build an
The tone you hear is the frequency of
the oscillator. Install different values
of capacitors in place of the 0.1µF
(C2) to change the frequency.
Replace the speaker with the motor and
fan. When there is mail, the light is
blocked from the photosensitive resistor
and the motor spins.
Turn the switch on. If there is light on
the photosensitive resistor, the
speaker will not make any sound.
Place your finger over the resistor
and now the speaker sounds. A
simple mail notifying system can be
made using this circuit. Install the
photosensitive resistor and the green
LED inside the mailbox facing each
other. When there is mail, the light is
blocked from the photosensitive
resistor and the speaker turns on.
Project #285
Mail Notifying
Electronic Fan
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