1. Make a Voltage Controlled Resistor
2.Use it to make a Voltage Controlled Oscillator
3.Use it to feed a signal into a laptop's microphone input.
The voltage controlled resistor is a very useful element in electronics. The one in this instructable takes a minute to make and does not require too much electronic knowledge to operate. It is made out of an LED and a Cadmium Sulfide (CdS) photocell. The LED changes light intensity with change of voltage/current. The photocell is a resistor that changes resistance with change in the intensity of light striking it.
To build a voltage controlled resistor, you need to glue the LED to the photocell then paint the whole assembly black to shut out ambient light. That's it!
The voltage controlled resistor can also be used to:
.Control devices like the volume of an amplifier
.Control gain in automatic gain control circuitry
.Feedback signals to control motors and robotics.
.Amplitude Modulate (AM) a signal.
Check out my other Instructables:
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Step 1: Application: Voltage Controlled Oscillator
VCOs are used in FM modulation, mainly. In this case, it used to make a two tone siren which you can see in operation in the video below
(Note: the flashing LED is part of the voltage controlled resistor assembly, I did not paint it black to show how it operates. My hand is changing the pitch of VCO because it is shutting out the ambient light that affects the exposed photocell)