Elenco Circuit Maker Sound Plus 200 - Manual (Page 28)

Project #40
Transistor Direction
Project #41
Another Transistor
Direction
-27-
Project #42
Turn on the slide switch (S1) and the LED (D1) lights; it will not be very
bright so turn off the room lights or hold your fingers around it to see it
better. Press the press switch (S2) several times very slowly; the LED
and lamp (L4) go on and off.
Press the press switch many times quickly - the lamp still goes on and
off but the LED stays on. Next, remove the 100mF capacitor (C4) from
the circuit - the LED goes on and off now. Why?
Pressing the switch quickly simulates a changing voltage, which turns
the LED on and off. The 100mF capacitor can store electricity, and it
combines with the NPN transistor (Q2) to simulate a rectifier. This rectifier
converts the changing voltage at the press switch into a constant voltage,
which keeps the LED on.
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.
Simple Rectifier
The press switch (S2) controls the
NPN transistor (Q2) and can turn
on the lamp. The slide switch
(S1), however, cannot control the
PNP transistor (Q1) and so
cannot turn on the lamp.
This circuit is similar
to the preceding one
except for the way
the transistors are
connected.
Now the press switch
(S2) cannot control the
NPN transistor (Q2)
and so cannot turn on
the lamp. The slide
switch (S1), however,
can control the PNP
transistor (Q1) and so
does turn on the lamp.
The two transistors are installed
the same way in the circuit but
work differently - current can
only flow in the direction of the
arrow marked on the part.
CM-200_Manual_031914.qxp_CM-200_Manual_031914 4/2/14 12:04 PM Page 28