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Project #85
NPN Light Control
OBJECTIVE: To compare transistor circuits.
Project #86
NPN Dark Control
OBJECTIVE: To compare transistor circuits.
Turn on the slide switch (S1),
the brightness of the LED (D2)
depends on how much light
shines on the photoresistor
(RP). The resistance drops as
more light shines, allowing more
current to the NPN (Q2).
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 (Q2).
Project #87
Red & Green Control
OBJECTIVE: To show how the adjustable resistor works.
Project #88
Current Controllers
OBJECTIVE: To compare types of circuits.
Turn on the circuit using the
slide switch (S1) and/or the
press switch (S2) and move
the adjustable resistor’s (RV)
control lever around to adjust
the brightness of the LEDs (D1
& D2). When the adjustable
resistor is set to one side, that
side will have low resistance and
its LED will be bright (assuming
the switch on that side is ON)
while the other LED will be dim
or OFF.
Build the circuit and turn on
the slide switch (S1), the LED
(D1) will be lit. To increase the
LED brightness, turn on the press
switch (S2). To decrease the LED
brightness, turn off the slide switch.
With the slide switch on, the 5.1KW
resistor (R3) controls the current.
Turning on the press switch places
the 1KW resistor (R2) in parallel
with it to decrease the total circuit
resistance. Turning off the slide
switch places the 10KW resistor
(R4) in series with R2/R3 to
increase the total resistance.
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