Active Listening Device. Utility Gadgets.5

You can now hear what is going on in your home premises. The speech, sounds etc will be heard inside the home. So a simple security measure for remote listening at night. You can switch on light if somebody makes whispering, outside the home ,may be an attempt for a burglary.

The circuit is a sensitive MIC amplifier using the Pre amplifier IC TL071 and a 2 watt Amplifier IC LM380. TL071 is the JFET Op amp with high gain and is commonly used in Tape Recorder’s Pre amp section. LM 380 is the low noise 2 watt Amplifier with a gain of 34dB.

Difficulty to see components? Click on the image for the enlarged view

Enclose the circuit with power supply in a Box and fix it in the Frame of Front/ Back door or Gate pillar. Place the 4 inch 8 ohms speaker inside the room. Connect it with the circuit using 1 core shield wire. Solder MIC directly on the PCB. Solder all components especially capacitors as close as possible with minimum lead length to prevent unwanted oscillations. Enclosing the MIC in a tube will further increase the sensitivity.

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