Elenco Projects 102-305 - Manual (Page 71)

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Project #293 Police Siren Amplifier
OBJECTIVE: To amplify sounds from the music integrated
circuit.
Build the circuit and turn on the slide switch (S1). You will hear a very
loud siren, since the sound from the alarm IC (U2) is amplified by the
power amplifier IC (U4). Sirens on police cars use a similar circuit,
with an IC to create the sound and a power amplifier to make it very
loud.
Project #294 Lasting Doorbell
OBJECTIVE: To build a doorbell
that stays on for a while.
OBJECTIVE: To build a
clicker that stays on for a while.
Place the 10 μ F capacitor (C3) on
top of the whistle chip (WC).
Press and release the press
switch (S2). It makes a clicking
sound that repeats for a while.
Build the circuit at left, note that there
is a 4-snap wire on layer 1 that is not
connected to a 3-snap wire that runs
over it on layer 3. Turn on the slide
switch (S1), then press and release
the press switch (S2). There is a
doorbell sound that slowly fades away.
When the press switch is pressed,
the transistors are supplied with
current for oscillation. At the same
time, the 100
μ F capacitor (C4) is
being charged. When the press
switch is released, the capacitor
discharges and keeps the oscillation
going for a while.
Project #295
Lasting
Clicking