INTERCOM SYSTEMS USING FM
BY
N.S.ANANDHA KUMARAN
BE EEE III YEAR,
nsanandhakumaran@gmail.com
K.L.N.CE
ABSTRACT:
The credential part of this paper gives the theoretical ideas regarding the Intercom systems using FM. At present two dominant types of intercom systems exist, the party-line and matrix Systems. In a party-line system, a common 2-wire cable ring connects together low-cost single-key user stations that conference with each other. In a matrix system all users have multiple keys to talk to selected destinations independently. The main disadvantage of using these two systems is that they are prone to noise and less efficient. To make the intercom more specific and to increase efficiency, we in our implementation devised an FM intercom system which is an integrated system of the following.
The intercom using frequency modulation can be grouped into two categories based on the necessary:
1. Simplex fm intercom.
2. Full duplex fm intercom.
Simplex communication uses a master intercom to communicate to different slave intercom .
Full duplex intercom consists of a master and a slave unit. The master and the slave intercoms are full duplex units with a single master unit at the control room and multiple slave units at the terminal ends.
The main difference between the simplex and full duplex intercom is that the simplex intercom is for conveying information in general or in specific, it cannot be used to get reply from the slave intercom.
This paper is only a theoretical analysis given and all the information provided are specifically organized by us with the help of few sources from internet.
INTRODUCTION:
An intercom (intercommunication device), talkback or doorphone is an electronic communications system intended for limited or private dialogue, direction, collaboration or announcements. Intercoms can be portable or mounted permanently in buildings and vehicles. Intercoms can incorporate connections to walkie talkies,telephones, cell phones and to other intercom systems over phone or data lines and to electronic or electro-mechanical devices such as signal lights and door latches.
Permanent intercoms installed in buildings are generally composed of fixed microphone/speaker units which connect to a central control panel by wires. A small home intercom might connect a few rooms in a house. Larger systems might connect all of the rooms in a school or hospital to a central office. Intercoms in larger buildings often function as public address systems, capable of broadcasting announcements.
Intercom is needed where many people work together in some common project, such as making a television program or directing a live event. For this to happen smoothly, so that responses to questions, commands, and instructions pass speedily between teams, the use of telephones soon becomes impractical. Consider a situation in which the Director is already in a call and blocks another incoming call from the studio Floor Manager to alert the production control room that a guest is not in place, and the Presenter should go to another item. This case of blocking highlights the difference between a telephone system and an intercom system. Unlike a telephone
System , the intercom system allows multiple callers to get to a destination, indicates who they are, and provides selective answering.
In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.
BLOCK DIAGRM :
EXPLANATION:
The intercom using frequency modulation can be grouped into two categories based on the necessary:
1. Simplex fm intercom
2. Full duplex fm intercom.
Simplex FM Intercom:
Simplex communication uses a master intercom to communicate to different slave intercom. In the Simplex FM Intercom, the master is a transmitter with various frequency to contact any specific slave intercom or single to a frequency to connect many slave intercoms to convey the information.
The slave is tuned to definite reception frequency to connect to the master intercom.
In case of conveying general information all the slave intercoms are tuned to single transmitting frequency of the master intercom and for conveying specific information the slave intercoms can be set to specific reception frequency from the master intercom
.
Full Duplex FM Intercom:
It consists of a master and a slave unit. The master and the slave intercoms are full duplex units with a single master unit at the control room and multiple slave units at the terminal ends like entry at various doors of the institution or campus.
The difference between the full duplex and simplex intercom is that the simplex intercom is for conveying information in general or in specific, it cannot be used to get reply from the slave intercoms.
The master intercom consists of full duplex unit (A separate transmitter and receivers in it) capable of accepting multiple input frequencies but tuned to only single transmitting frequency to connect to specific slave intercom receives. The master intercom can be tuned to various frequencies to select specific slave intercom for communication. The master unit helps to know the controller about the incoming lines from various slave intercoms. Queuing technique or priority level can be used here as per the preference. The other slave intercom can then be connected to communicate.
The slave intercom is tuned to a definite transmitting and receiving frequency to communicate with the master intercom unit. The slave intercom is not tunable .thus a double side communication is possible between the controller and the stranger.
The slave intercom has a push button switch which helps to turn on the slave intercom from sleep .When the conversation is stopped the slave intercom comes to sleep mode as a measure to reduce the power consumption of the system . The push button can also be a calling bell and the above mentioned technique can be used to communicate to the person inside the home.
Master intercom is kept active around the clock to receive the signal from any intercom trying to connect the master intercom.
For further improvement of security, the above given system is connected to a voice recognition system at the master intercom and this can be used to operate automatic doors from control room.
MERITS AND DE MERITS:
The greatest advantage of the fm intercom is that it can be built cheaper for two terminal bi directional usage and simplex unidirectional usage.
The construction and implementation of such intercom is easier even in apartments where the installation of wired intercom is costly .
voice recognition can be added in the controlling end for better identification in security needs usage
Taking into account the demerits of the fm intercom system ,
The video conferencing intercoms which is most preferred in the higher end safety like in industries , it cant be used .
APPLICATIONS:
Some of the applications where fm intercom system can be used are :
In household safety to communicate with the strangers without opening the doors . Here full duplex fm intercom is advisable
In industrial sector , fm intercom can be used to convey information to the workers by the controller(eg.manager) with receiver intercoms placed in the manned working areas in the industry and the main intercom with in the control room.
CONCLUSION:
The paper is just a theoretical justification. But the recent advancement in the field of communication gives the hope of the effective use of this technology in intercom systems. This paper starts by giving an introduction to intercom systems using FM and its importance as recognized by various other technocrats. This field of communication is developing faster and we could expect a lot more efficient systems in near future.
REFERENCES:
Principles of Electronic Communication System, by Louis Frenze.
Modern Electronic Communication, by Jeff Beasley and Gary M. Miller.
Web search:
http://en.wikipedia.org
www.fancomm.com
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