Pk.docx

1. INTRODUCTION

During the functions and festivals to address the people there is the need of the public addressing system (PAS). This system consists of the Audio Amplifier which amplifies the sound. The Audio Amplifier amplifies or in simple language it increases the strength of the input signal. Our project is type of Audio Amplifier which also amplifies the input signal. Our project can be used in the Public Addressing System (PAS) and also in the Music system, we have designed our project for the purpose of the musical system. An audio amplifier is an electronic device, that is used to increase the amplitude strength of audio signals that flow through it. These amplifiers strengthen low-power audio signals to a level which is appropriate for driving loudspeakers. At the simplest level, an amplifier is an electronic circuit which allows a small input voltage/signal to control a much larger voltage (or current) through either a semiconductor junction or the grid of a tube, using them as a "flow adjuster" for the electrons passing through the higher voltage device. We have designed Audio Amplifier circuit using Operational Amplifier IC 386. Operational Amplifier IC 386 is specially designed audio amplifier IC. IC 386 is a audio amplifier IC designed for the purpose to address small crowd and as music system for the small hall. LM386 is a low voltage audio amplifier and frequently used in battery powered music devices like radios, guitars, toys etc. LM386 has a wide supply voltage range 4-12v. Due to its small battery requirement and high gain relatively, it has lots of applications in various small devices. It is very compact and compatible. It has various application as it can be used as oscillator, square wave generator, radio amplifier

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2. COMPONENTS LISTS

Sr. No.

Name

Quantity

1.

LM386 (Audio Amplifier)

1

2.

8-Pin IC socket

1

3.

Capacitors (10µF)

2

4.

Capacitor (220µF)

1

5.

Capacitor (0.05µF)

1

6.

Capacitor (0.1µF)

1

7.

Resistor (10KΩ)

1

8.

Potentiometer (100KΩ)

1

9.

Speaker (8Ω)

1

10.

Head-Phone jack (Male)(3.5mm)

1

11.

General-PCB-Bread-board (6.5cmX5.5cm)

1

2

3. SYSTEM DESCRIPTION

3.1. Pin Description: -

Pin description of LM386 is given below along with the functions of external components used for amplification.

(Figure 3.1: LM386 Pin Diagram)

Pin 1: It is used to adjust the Gain of IC 386 between the variable range of 20 to 200 by using the variable capacitor of proper value. Pin 2: It is the negative input terminal of the IC 386 it is normally connected to ground. Pin 3: It is the positive input terminal of the IC 386 it is connected to the input sound signal. Pin 4: This terminal of the is used to connect to the ground. Pin 5: The amplified output signal is obtained from this pin. Pin 6: The power supply between the range of 4v-12v is connected to this pin. 3

Pin 7: This pin is used as the bypass pin which used to bring stability to the output signal. Pin 8: This pin is also used to adjust the Gain of IC 386 between the variable range of 20 to 200 by using the variable capacitor of proper value.

3.2. Working of Audio Amplifier: -

PIN 1 and 8: These are the gain control PINs, internally the gain is set to 20 but it can be increased up to 200 by using a capacitor between PIN 1 and 8. We have used 10uF capacitor C1 to get the highest gain i.e. 200. Gain can be adjusted to any value between 20 to 200 by using proper capacitor.

Pin 2 and 3: These are the input PINs for sound signals. Pin 2 is the negative input terminal, connected to the ground. Pin 3 is the positive input terminal, in which sound signal is fed to be amplified. In our circuit it is connected to the positive terminal of the condenser mic with a 100k potentiometer RV1. Potentiometer acts as volume control knob. A capacitor C5 of 0.1uF has also been used along with potentiometer, to remove the DC component of input signal and only allow audio (AC component) to be fed into LM386.

Pin 4 and 6: These are the power supply Pins of IC, Pin 6 for is +Vcc and Pin 4 is Ground. The circuit can be powered with voltage between 5-12v.

Pin 5: This is the output PIN, from which we get the amplified sound signal. The output signal has both AC and DC component, and DC component is undesirable and can’t be fed to Speaker. So, to remove this DC component, a capacitor C2 of 220uF has been used. This has the same function as Capacitor C5 (0.1uF) at input side. Along with this capacitor, a filter circuit of Capacitor C3 (.05uF) and resistor R1 (10k) has been used at the output PIN 5. This filter also called the “Zobel network”, this electronic filter is used to remove the sudden High frequency oscillations or noise.

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Pin 7: This is the bypass terminal. It can be left open or can be grounded using a capacitor for stability. This LM386 audio amplifier circuit can be also used to record any sound. We just need a 3.5 mm audio plug and a computer with sound recording software. We only need to connect computer’s 3.5mm jack in place of Speaker, using 3.5mm audio plug, and we can easily record our voice or any sound into computer like a professional microphone. In our project we have connected the 3.5mm (Male) head-phone for the input so in figure 4.2 we just have to remove the condenser microphone and the resistor R 2 which is used as pull up resistor for the microphone.

(Figure 3.2: Circuit Diagram of LM386 as an Audio Amplifier along with Microphone input (of Gain 200))

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4. ADVANTAGES

1) Low Voltage Amplifier. 2) Small size Amplifier circuit. 3) Variable and easy to control gain. 4) Not more requirements of external component for design of the amplifier circuit. 5) It can be used as small Public Addressing System.

(Figure 4.1. Image of the Audio Amplifier Using LM386 )

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5. DISADVANTAGES

1) It has low gain relatively. 2) Even with the use of filters in the circuit their lot of noise in the output.

(Figure 5.1. Image of the Audio Amplifier with in the Plastic Compartment )

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6. APPLICATIONS

1) AM-FM radio amplifier 2) Portable tape player amplifier 3) Intercom 4) TV sound system 5) Line drivers 6) Ultrasonic drivers 7) Small servo drivers 8) Power convertors

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7. FUTURE SCOPE

In our project we think to make it portable by the addition of the Rechargeable Battery and we are also thinking to make it wireless i.e. By adding an Bluetooth Module to the input along with the 3.5mm headphone both Male and Female so that we can use it as the Public Addressing System (PAS) also. We are also planning to add an USB port for input and also to add the radio receiver circuit so that we can use it as a portable FM player and also to play the songs in the pen-drives or memory cards.

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8. REFERENCES

1) https://circuitdigest.com/electronic-circuits/lm386-audio-amplifier-circuit 2) https://www.youtube.com/watch?time_continue=4&v=zZ4c5Oz41WE 3) https://www.alldatasheet.com/view_datasheet.jsp?Searchword=LM386

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