User Guide

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Project #296
OBJECTIVE: To show how capacitors can leak.
Build the circuit (be sure the positive (+) side of the capacitor is
towards the left) and turn on the slide switch (S1). The green LED (D2)
will flash brightly as the 470μF capacitor (C5) charges up and then
becomes dim but will not be off. When you turn off the slide switch, the
red LED (D1) is initially bright, but goes dim as the capacitor
discharges itself through it.
Why doesn’t the green LED•go off after the capacitor becomes
charged? It is because current is leaking through the 470μF capacitor.
The positive (+) side of the capacitor should normally be facing
towards the higher voltage side, in this circuit we have it facing away
from the batteries (B1). In most circuits this doesn’t matter, but in this
case it does.
Reverse the position of the capacitor (so the positive (+) side is on the
right) and turn on the slide switch again. Now the green LED turns
totally off after the capacitor gets charged up. It doesn’t leak now.
Leaky Capacitor
Project #297 Transistor Fading Siren
OBJECTIVE: To build a siren that
slowly fades away.
OBJECTIVE: To build a
doorbell that slowly fades away.
Replace the alarm IC (U2) with
the music IC•(U1). The circuit
has a doorbell sound that plays
and stops.
Turn on the slide switch (S1), then
press and release the press switch
(S2). You hear a siren that slowly
fades away and eventually goes off.
You can modify this circuit to make
machine gun or ambulance sound
instead like in the other projects. You
can also replace the 10μF capacitor
(C3) with the 100μF (C4) or 0.1μF
(C2) to greatly slow down or speed
up the fading.
Project #298
Fading
Doorbell