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SOUND SENSOR

A device that detect our voice.

It is very simple!

Generally we use for sensing the sound a “CONDENSER MICROPHONE”

Condenser Microphones

Condenser means capacitor, an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuck as the name for this type of microphone, which uses a capacitor to convert acoustical energy into electrical energy.

Condenser microphones require power from a battery or external source. The resulting audio signal is stronger signal than that from a dynamic. Condensers also tend to be more sensitive and responsive than dynamics, making them well-suited to capturing subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity makes them prone to distort.

How Condenser Microphones Work

A capacitor has two plates with a voltage between them. In the condenser mic, one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. Specifically, when the plates are closer together, capacitance increases and a charge current occurs. When the plates are further apart, capacitance decreases and a discharge current occurs.

A voltage is required across the capacitor for this to work. This voltage is supplied either by a battery in the mic or by external phantom power.

Cross-Section of a Typical Condenser Microphone

CIRCUIT DIAGRAM FOR WORKING OF A CONDENSER MICROPHONE

Cell is supply operating voltage.

Voltage across RC network is same as apply voltage.

Apply  KVL

Vc = Vcc - i*R

At steady state capacitor act as a open switch,i become zero and output voltage is same as +Vcc supply.

But due to change in capacitance i change and hence voltage signal are generate.

Vari the value of resistance R,we change sensitivity.

Generally value of R is near about 15 kilo oms.

Do you know a loudspeaker is also used for sound sensing. Genaraly we use it for generation of sound.it is also known as speaker.

But how?Do u know?

We know that when a conductor placed in a magnetic field then it experience a foece.

Same thing is apply in case of speaker.

The most common type of driver uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier.

It is the working of speaker.

Now the reverce process is when we spoke in air then vibrating air come in contact with speaker diagraph, also vibrate coil.

Due to electromegnatic induction EMF signal are generate.That can be amplified.

I shall told you how we can do it.

Now we learn about amplifier networks.

What is amplifier?

Generally, an amplifier or simply amp, is any device that changes, usually increases, the amplitude of a signal. The relationship of the input to the output of an amplifier—usually expressed as a function of the input frequency—is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain.

A simple amp network is given hear.

A weak signal (small amplitude) is apply input terminal and amplified signal can be obtained at output terminal.

Resistance R1 and R2 give operating supply at transistor emitter base junction.

CASE 1: When input signal is not apply.

In this case base current are constant and don’t reach thr output terminal due to capacitor Cout DC bloking capability.

CASE 2: Now input signal is apply.

Now there some variation in base current which are amplified and reach at collector atwhere it filter by capacitor Cout.

If k is the ratio of collector currentand & base current

then,we have

Vcc – IcR3  -  VCE   =  0