Elenco Snap Circuits Motion - Manual (Page 76)

Project 157 Red Just Before Yellow
Turn on the slide switch (S1). Set the switcher (S6) to both the left &
right positions at several settings on the adjustable resistor (RV2), and
compare the brightness of the red/yellow bicolor LED (D10). See if you
can notice a difference in the LED brightness between red and yellow,
especially when the LED is very dim.
Now move S1 from the points marked C & D to the points marked A &
B. Move RV2’s lever around again while changing S6 between left and
right, comparing the LED colors and brightness.
Project 156 Red Lights First
Set the switcher (S6) to the middle position and turn on the slide switch (S1). Set
the lever on the adjustable resistor (RV2) all the way to the left. The color LED
(D8) should be on, but may be mostly red. Slowly move the lever on RV2 to the
right until the LED is completely off. Notice that the red color stays on the longest.
Now set S6 to the right position and adjust RV2 again, watching the LED colors.
Blue and green color may also appear now, but may go dim before red does.
Now move S1 from the points marked C & D to the points marked A & B and set
S6 back to the middle position. Move RV2’s lever around again, watching the LED
colors and brightness. Set S6 to the right position again, and notice that the LED
now lights for a much larger part of RV2’s adjustment range.
-75-
Yellow light is just slightly easier for the
red/yellow bicolor LED to produce than
red light. If you look closely at the LED
when it is dim, then you may notice that
red color is slightly brighter than yellow.
The voltage needed to turn on an LED depends on the light color. Red
needs the least voltage, and blue needs the most. With S1 at points C
& D and S6 in the middle position, the voltage to the color LED is lowest,
and may barely be enough to turn on the red color. Setting S6 to the
right position bypasses the NPN transistor (Q2), and boosts the LED
voltage a little. Shifting S1 to points A & B increases the circuit voltage
from 3V to 6V, making the LED work for a greater part of RV2’s range.
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