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Circuits
Using a single cable such as speaker
wire or doorbell cable, this circuit can be remotely
positioned, for example, at the bottom of a garden or
garage, and used to detect all sound in that area. The
cable can be buried in a hosepipe or duct and is
concealed out of sight. The mic is an ordinary dynamic
mic insert and should be housed in a waterproof
enclosure with the rest of the circuit.
The mic output is amplified by the two
transistors, the output is fed down the cable via the
220u capacitor. Here, it has a dual purpose of
preventing the DC supply from upsetting the bias of the
circuit, and also allowing the smaller ac audio output
to pass down the line. At the power supply, the audio is
recovered by the 10k preset and 220u capacitor. It is
used to feed a small audio amplifier (such as the 2watt
design) shown earlier on this site. |
