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40
Project 81 Resistance Director
Move the lever on the adjustable resistor (RV) across its range and
watch the brightness of the white and color LEDs (D6 & D8).
Replace either LED with the red LED (D1) and compare it too.
You can also replace one of the battery holders (B1) with a 3-snap
wire, and compare the LED brightnesses at lower voltage.
The adjustable resistor can be
adjusted from about 200 ohms to
about 50,000 ohms.
The white LED is a super-bright
LED, so will be brighter than the
others at comparable resistance.
Project 80
Air Pressure Light Control
Project 79
Photo Light Control
Turn on the switch (S1). Control
the white LED (D6) brightness by
varying the amount of light on the
photo-transistor (Q4). Try holding
the red, green, and blue lters
over the phototransistor and see
how they affect it.
Replace the white LED with
the red LED (D1) or the color
LED (D8) and compare them.
Blow on the microphone (X1).
The white LED (D6) will icker,
because the resistance of the
microphone changes when you
blow on it.
Talking into the microphone also
changes its resistance, but you
will not be able to notice the
difference here.
You can replace the white
LED with the red LED (D1) or the
color LED (D8), but they will not
be very bright.
The phototransistor uses light to control
electric current. As more light shines on
the phototransistor, the current through
it increases, making the LED brighter.
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