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49
Photoresistor Control
OBJECTIVE: To use a photoresistor to control the brightness of an LED.
In this circuit, the brightness of the LED (D1) depends on how much light
shines directly on the photoresistor (RP). If the photoresistor were held
next to a ashlight or other bright light, then the LED would be very bright.
The resistance of the photoresistor decreases as more light shines on it.
Photoresistors are used in applications such as streetlamps, which come
on as it gets dark due to night or a severe storm.
Project #132
Project #134
Set the adjustable resistor (RV) to the bottom position and then turn the
slide switch (S1) on. The LED (D1) will start ashing at a frequency of
0.5Hz (once every two seconds). Slowly adjust the adjustable resistor and
the LED ashes faster. As the frequency increases, the LED ashes faster.
Eventually, the LED ashes so fast, it looks like it is on all of the time.
Oscillator 0.5 - 30Hz
OBJECTIVE: To build a 0.5Hz - 30Hz oscillator that will light an LED.
Use the circuit from project #132.
Connect a single snap under the speaker (SP) and then connect it across
the LED (on level 4). Turn the slide switch (S1) on and now you can hear
the oscillator. Adjust the adjustable resistor (RV) to hear the different
frequencies. Now you can hear and see the frequencies. Note: You may
not hear sounds at all settings of the adjustable resistor.
Project #133
Sound Pulse Oscillator
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