Elenco Electronics 202 - Manual (Page 67)

-66-
Project #142
Current Controllers
OBJECTIVE: To compare
types of circuits.
Build the circuit and turn on the slide
switch (S1), the LED (D1) will be lit.
To increase the LED
brightness,
press the press switch (S2). To
decrease the LED brightness, turn
off the slide switch.
With the slide switch on, the 5.1K Ω
resistor (R3) controls the current.
Turning on the press switch places
the 1K
Ω resistor (R2) in parallel with
it to decrease the total circuit
resistance. Turning off the slide
switch places the 10K
Ω resistor (R4)
in series with R2/R3 to increase the
total resistance.
Project #143
NPN Dark Control
OBJECTIVE: To compare
transistor circuits.
Turn on the slide switch (S1),
the brightness of the LED (D2)
depends on how LITTLE light
shines on the photoresistor
(RP). The resistance drops as
more light shines, diverting
current away from the NPN
transistor (Q2).
Project #144
PNP Light Control
OBJECTIVE: To compare
transistor circuits.
Project #145
PNP Dark Control
Turn on the slide switch (S1),
the brightness of the LED (D1)
depends on how much light
shines on the photoresistor
(RP). The resistance drops as
more light shines, allowing more
current through the PNP
transistor (Q1). This is similar to
the NPN circuit above.
OBJECTIVE: To compare
transistor circuits.
Turn on the slide switch (S1),
the brightness of the LED (D1)
depends on how LITTLE light
shines on the photoresistor
(RP). The resistance drops as
more light shines, so more
current gets to the 100k
Ω
resistor (R5) from the
photoresistor path and less from
the PNP-diode path. This is
similar to the NPN circuit above.