Relay control using mic and sound amplifier

During late night we often face problems from disturbances created by stray animals, unknown people and other moving objects which are quite annoying. At times such unwanted disturbances can even scare you in night. This circuit based project presented here can protect you from such unwanted movements of people and animals.

This relay control circuit detects the presence of animals and human beings and alerts them by raising a false alarm in form of light.Whenever any unwanted sound is produced, it gets detected by the sound sensor. The weak signals are amplified by the amplifying unit, which in turn signal the relay to switch on and glow the bulb to scare the intruder. The transistor T3 is used in the switch mode configuration to turn on the relay whenever some sound is detected.

The circuit of the project shown here detects the presence of a human being or animal from the sound they produce while talking or making some movements. A condenser mic is used to sense such sound signals from the surroundings and converts them into weak electrical signals, which are then fed to the amplifying unit.

The amplifying unit uses a combination of two transistors to amplify the weak signals. For detail description of the amplifying unit please refer to the sound amplifier circuit . The signals amplified by the transistors are used to drive a relay. The coil of the relay is connected between the VCC and the collector of the transistor T3. The other side of the relay is connected to an electric bulb as shown in the diagram.