Elenco Projects 102-305 - Manual (Page 68)

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Project #284 Mail Notifying Electronic Bell
OBJECTIVE: To build a circuit to
indicate if you have mail by
sounding a tone.
OBJECTIVE: To build a flicking
LED circuit.
Use the circuit from project #286.
Replace the speaker (SP) with a red
LED (D1, 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 activating
the lamp.
Project #286
OBJECTIVE: To build an
oscillating circuit.
The tone you hear is the frequency of
the oscillator. Install different values
of capacitors in place of the 0.1
μ F
capacitor (C2) to change the
frequency.
Replace the speaker (SP) with the lamp
(L2). When there is mail, the light is
blocked from the photoresistor (RP) and
the lamp lights.
Turn on the slide switch (S1). If there
is enough light on the photoresistor
(RP), the speaker (SP) will not make
any sound. Place your finger over the
photoresistor and now the speaker
sounds. The sound will stay on until
you turn off the slide switch. A simple
mail notifying system can be made
using this circuit. Install the
photoresistor and the green LED
inside the mailbox facing each other.
When there is mail, the light is
blocked from the photoresistor and
the speaker turns on.
Project #285
Mail Notifying
Electronic Lamp
Twice-
Amplified
Oscillator