Construction Of A Full-Duplex Intercom System

Project and Seminar Material For Electrical Electronics Engineering EEE

Project and Seminar Material For Electrical Electronics Engineering EEE


The design of full duplex intercom system is an absolute implementation of strategic components to perfect a modern semi-conductor technology (electronics) and communications. The simple circuit design allows the two intercom stations to be operated leaving the operation free of the usual “push-to-talk” operation mode, no complex changeover switch is required.

As both microphones are always in operation, a special circuit is used to avoid that the loud speaker output is being picked up by the microphone enclosed in the same box, causing a very undesired and loud “howl” i.e. the well known “Larson effect”. A private switch allows microphone muting, if required.

Table Of Content

Preliminary Page(s)

  • Title page
  • Certification page
  • Dedication
  • Acknowledgement
  • Table of content
  • Abstract

Chapter One

1.0 Introduction

  • 1.1 Preamble
  • 1.2 Intercom system
  • 1.3 Design objectives

Chapter Two

2.0 The review of Related Literature

  • 2.1 Car Com
  • 2.2 Mini Gard
  • 2.3 Public III
  • 2.4 Claro
  • 2.5 Gard MC
  • 2.6 Modems
  • 2.7 Classification of modems according to operational mode
  • 2.8 Screened cable
  • 2.9 TDA 7052 BTL mono audio amplifier

Chapter Three

3.0 Basic Design and Construction

  • 3.1 Design approach
  • 3.2 Description of individual component used
  • 3.3 System construction description
  • 3.4 Description of the system building block
  • 3.5 The Construction Techniques
  • 3.6 Comments on construction

Chapter Four

4.0 Testing and Trouble Shooting

  • 4.1 Introduction to Testing
  • 4.2 Component testing
  • 4.3 Testing of circuit parameters
  • 4.4 Powering the circuit
  • 4.5 Packaging
  • 4.6 Cost Analysis

Chapter Five

5.0 Conclusion and Recommendation

  • 5.1 Conclusion
  • 5.2 Recommendation
  • Bill Of Quantity
  • Reference

Chapter One


1.0 Preamble

This project is on the design and construction of a full duplex intercom system. The design is such that the full duplex intercom will be used to enable two parties to signal and communicate with each other without interference.

1.1 Intercom System

Intercom is a short form for intercommunicating telephone. An intercom uses relating two-wire system, two for transmitting and two for reception (full duplex) and cannot be used on normal exchange lines. It is electronic communication system within a building or group of buildings.

Intercom (i.e. wireless intercom) aims to be a high quality voice communication tool use on the internet or local area networks. Intercoms are generally composed of fine microphones/speaker units which connect to central control panel. A small home intercom might connect a few rooms in a house; large systems might connect all the rooms in a school or hospital to a central office.

Intercoms in large buildings often function as public address systems, capable of broadcasting announcements.
Therefore a full duplex intercom is a situation whereby two people simultaneously talk to each other without interference or loss of signal power. Its connection is different between the door stations and the inside station.

1.2 Design Objectives

A general objective of the present invention is to provide local intercom circuit arrangement for use with and between multiple, similarly configured telephone instruments interconnected by common local cabling so as to overcome the drawbacks of an advance state of the prior art.

One specific objective of the invention is to provide a full duplex intercom arrangement by employing a dual frequency FM radio carrier talk circuit coupled to a single telephone system subscriber line (tip and ring wire pair or optical path) using two carrier frequencies sufficiently separated specifically as not to cause audible interference with each other and as not to cause interference with the use of the lines for conventional telephone communications.

Another specific objective of the present invention is to provide a full duplex intercom circuit arrangement by employing single frequency FM radio carrier talk circuits over two of the locally extending telephone company subscriber lines.

A further specific objective is to provide a full duplex intercom circuit arrangement with a frequency modulated carrier or carriers imposed locally on a telephone cable in a manner which does not cause any interference with telephone system signaling or central office equipment.

One more specific objective is to provide a full duplex intercom circuit which is easily operated, which is fully contained in a user telephone instrument, which requires very little power for operation, which may be manufactured and installed in the instrument at low cost and which has a long and reliable useful life in the telephone environment, glad to say that this is our project objective.



Chapter Five

5.0 Conclusion And Recommendation

5.1 Conclusion

It shall sound insolvent to say that this project was achieved at a platter of gold. The success of this work is a dividend of careful research, practice and commitment; also it is a guarantee of a sound knowledge of electronics components and its implementation in communication.

During the execution of this project, more knowledge were acquired which if this kind of work is made a constant practice, the sky will be our limit in the field of electrical electronics, particularly communication and electronics option.

Where much problem was encountered in this work was on the purchase of the component since it was costly and some were even purchased at Onitsha at an additional transportation cost which increased the production cost. Considering this, if the component purchases are made in bulk from the producers, this will go along way to reduce cost. Another tactical area was in the selection of the trimmer for effective impedance matching at the output of the one unit to the input of the second unit after the pre-amps stage. Hence student should always be patience when encountering such a difficulty. In addition, if a screen cable cannot be used, a power line carrier communication can be engaged as the transmission medium between the two spots where he PHCN wire cable can be used as the medium for communications and this will reduce the product cost.

To use this system for large industrial premises or other large premises, a multiplexer control unit with PC is incorporated to the system. Other technologies associated to the system is the wireless where electromagnetic waves that carries the information signal will be transmitted through the air using an RF transmitter which a RF receiver will receive it at the reception terminal and convert it back to the original information through decoder.

This technology though costly but will make the intercom system more reliable and flexible just like the handsets.
We belief that more research shall yield more innovation on this technology to really make it stand the test of time.

5.2 Recommendation

Careful research and analysis has revealed the relevance of intercom system in the various facet of our society. The importance of this facilities to human endeavour has outsmart the cost of it production because the implementation of this technology will go along way to save cost in the world of information management, just like as the GSM technology is doing today. The relevance of this technology ranges from domestic home utility (toilets, kitchen, bedroom, door gates etc) industrial premises utility, security services utility, public service utility and many more. It is rather unfortunate that the public has not gotten the orientation on the utility of this diversified utility gadget due to the presence of the GSM supplement. The good news about intercom system is that it is not cost intensive to installed, it has no service cost attachment.

The cost involvement in this project actualization can be reduced by employing the principles of mass production where component will be imported from the production company in mass quantity and the gadget also produced in mass quantity with different designs particularly in a reduced size.

At this juncture, we urge our young engineering technocrats, government, NGO, financial houses to join hands together and advance this country technologically by encouraging local technology.

Construction Of A Full-Duplex Intercom System

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