Instructables

Make a Voltage Controlled Resistor and Use It

Step 3: A Signal Decoupler

A signal decoupler electrically isolates two devices while passing a signal between them. This is very important in cutting out interference noise and for safety.

In the previous example, I used a voltage controlled resistor to decouple and feed the tone from the VCO into my laptop's microphone input.

This setup reduces the noise that my laptop's microphone input can pick up from the circuit and protects my laptop from the circuit (you can burn the microphone input if you put too much voltage into it) .

I will show two configurations to decouple a laptop microphone input. The two configurations are based on the type of laptop microphone input. There are some laptop microphone inputs that provide power to the microphone and some that don't.
 
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