01-06-2013, 01:05 PM
WIRELESS INTERCOM SYSTEM
[attachment=54616]
INTRODUCTION:
The word ‘intercom’ means inter communication. It is a system in which each particular device is able to communicate with each other device . This is a wireless intercom and it works on the same principle as that of radio. It is always incorporated in a small radius,ie;in a building,offices,banks,schools etc; The system can have N number of devices.here we have taken N=4.ie; four devices A,B,C and D. Each device has its own separate transmitter, receiver, microcontroller and dtmf circuit. The device A can communicate with B,C or D by just pressing the switch corresponding to that particular device. If A is communicating with B, then at same time C can communicate with D without any interference. In case C wants to call A while it is communicating with B, there is an led that glows to show that the latter is busy. This busy line indication is done using dtmf. The switching and tunning is done by the microcontroller.
WIRED VS. WIRELESS
As mentioned one of the main reasons to use a wireless intercom system is that the cost of retrofitting a building for a wired intercom system is high. Another reason to use a wireless system is portability. With many wired systems a user who is seated typically has to get up and go to a wall mounted intercom to use it. There are a few systems that have desktop intercom units. With a wireless intercom, a person can put an intercom unit anywhere they want. Most require AC power so they still need to be near an electrical outlet. Other units are battery powered so they can be carried around from location to location.
One of the challenges of a wireless system is the possibility of interference. Since wireless systems communicate over the airwaves other wireless devices may interfere with wireless intercom communications. Higher quality wireless intercoms reduce or eliminate this interference by using such technology advances such as "digital spread spectrum".
Encrypted wireless
Wired intercom is inherently private, so long as the wiring system isn't tapped by outside parties. Wireless intercom is not inherently private; conversations on a wireless intercom are broadcast using publicly available wireless frequencies which means other users with similar devices could listen in if they are within range. Most units on the market will allow intercom conversations to be heard through other devices such as scanners, baby monitors, cordless telephones, or the same brand of wireless intercom.
Wireless intercom privacy can be provided if the audio stream is encrypted.
But here we are not using encrypted wireless due to the complexity and cost involved.
FREQUENCY RANGE
There are several frequency ranges for wireless intercom systems and other wireless products. Here we use the frequency range from103-108MHz.
The frequency that will work best for an application depends on the wireless devices already in use not only in the building itself, but also in surrounding buildings. For instance, if a residence is using wireless networking which operates in the 2.4GHz range, a wireless intercom that operates in this range may interfere with the network or vice versa. Ideally the best intercom for an application would be one that is in a frequency not in use in the surrounding area, or one that uses digital spread spectrum to reduce possiblity of interference.
CHOOSING A WIRELESS INTERCOM SYSTEM
There are two major benefits of a wireless intercom system over a traditional wired intercom. The first is that installation is much easier since no wires have to be run between intercom units. The second is that you can easily move the units any time.
With a wireless intercom system, you can be up and running minutes after you take them out of the box and power them up.
But with that ease of installation and convenience also comes some risk. There is risk of interference from other wireless and electrical devices. Other wireless devices near the intercom such as cordless telephones, wireless data networks, and remote audio speakers can interfere. Electrical devices such as motors can also cause noise.
There is also risk of other people hearing your conversations by picking up your conversation on a scanner, baby monitor, cordless phone, or a similar device on the same frequency. However, there are wireless intercoms that reduce or eliminate both of these risks.
MICROCONTROLLER…………
TRASMITTER
A transmitter is an electronic device which, usually with the aid of an antenna, propagates anelectromagnetic signal such as radio, television, or other telecommunications
In radio electronics and broadcasting, a transmitter usually has apower supply, an oscillator, a modulator, and amplifiers for audio frequency (AF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto thecarrier frequency, which is then broadcast. Generally and incommunication and information processing, a transmitter is any object (source) which sends information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a transmitter. Most devices on the market typically have a short range of up to 30 feet (9 metres) with any average radio (up to about 75 feet (23 metres) with a very good radio under perfect conditions) and can broadcast on any FMfrequency from 76.0 to 108.0 MHz
FM transmitters are usually battery driven, but some use thecigarette lighter socket in cars, or draw their power from the device itself.
LIMITATIONS
• The relatively low power output of FM transimitters sometimes makes it unsuitable for use in some large urban areas because of the number of other radio signals. This is compounded by the fact that strong FM signals can bleed over into neighboring frequencies making the frequencies unusable with the transmitter.
Specification: 4-channel, Modulation mode range 50HZ - 15KHZ wide band High-clarity , full -stereo sound Synonym preference < - 60dB Power light and frequency LED indicator Size : (L) 88mm x (W) 42mm x (H) 20mm Color : white
DTMF
DTMF ENCODER
The DTMF encoder is an encoder is an 18 pin IC. Here we are using SH91214B.It generates high and low frequency according to the selection made.When we make a selection in the 4*3 matrix, it produces a multi-frequency signal.This signal is called dual tone multi frequency.A low frequency row and high frequency column represent each selection.Each row and column has its own specific frequency.When a particular selection is made,the corresponding row and column is activated and produces an output. The circuit contains RC network(R1,R2,R3,R4) and (C1,C2,C3).According to the time duration the encoder IC produces the generation.The IC contains filters and frequency dividing networks. These network generates separate frequency for rows and columns. We can convert this IC pulse configuration by changing the status of a particular pin.The Vcc of the IC ranges from 3V to 5V. We usually use a 3.3Vzener for giving Vcc.The output of the coder IC is in the digital form.
DTMF ENCODER CIRCUIT.
DTMF DECODER
The basic function of a decoder is to detect the presence of a specified combination of bits on its inputs and to indicate that presence by a specified output level.In its general form, a decoder has ‘n’input lines to handle ‘n’ bits and form one to 2^n output lines to indicate the presence of one or more n-bit combinations.
The DTMF decoder consists of an 18 pin IC HT9170B.This is a complete DTMF receiver designed to detect standard DTMF signals. It generates a combination of high and low frequency according to the selection status. It includes a differential input amplifier, filter section and decoder section and storing logic circuits.The differential input amplifier allows adjustment of gain and choice of input configuration. The filter section a dial tone filter for dial tone rejection and separates the dial tone signal into low group and high group tones.
Features
• Full DTMF receiver in 18-pin plastic packages.
• Single 5V power supply.
• Internal gain setting amplifier.
• Adjustable guard time
• Built in dial tone filter
• Uses inexpensive 3.58MHz crystal
• CMOS for low power consumption
• Tri state outputs
• Early steering outputs.
[attachment=54616]
INTRODUCTION:
The word ‘intercom’ means inter communication. It is a system in which each particular device is able to communicate with each other device . This is a wireless intercom and it works on the same principle as that of radio. It is always incorporated in a small radius,ie;in a building,offices,banks,schools etc; The system can have N number of devices.here we have taken N=4.ie; four devices A,B,C and D. Each device has its own separate transmitter, receiver, microcontroller and dtmf circuit. The device A can communicate with B,C or D by just pressing the switch corresponding to that particular device. If A is communicating with B, then at same time C can communicate with D without any interference. In case C wants to call A while it is communicating with B, there is an led that glows to show that the latter is busy. This busy line indication is done using dtmf. The switching and tunning is done by the microcontroller.
WIRED VS. WIRELESS
As mentioned one of the main reasons to use a wireless intercom system is that the cost of retrofitting a building for a wired intercom system is high. Another reason to use a wireless system is portability. With many wired systems a user who is seated typically has to get up and go to a wall mounted intercom to use it. There are a few systems that have desktop intercom units. With a wireless intercom, a person can put an intercom unit anywhere they want. Most require AC power so they still need to be near an electrical outlet. Other units are battery powered so they can be carried around from location to location.
One of the challenges of a wireless system is the possibility of interference. Since wireless systems communicate over the airwaves other wireless devices may interfere with wireless intercom communications. Higher quality wireless intercoms reduce or eliminate this interference by using such technology advances such as "digital spread spectrum".
Encrypted wireless
Wired intercom is inherently private, so long as the wiring system isn't tapped by outside parties. Wireless intercom is not inherently private; conversations on a wireless intercom are broadcast using publicly available wireless frequencies which means other users with similar devices could listen in if they are within range. Most units on the market will allow intercom conversations to be heard through other devices such as scanners, baby monitors, cordless telephones, or the same brand of wireless intercom.
Wireless intercom privacy can be provided if the audio stream is encrypted.
But here we are not using encrypted wireless due to the complexity and cost involved.
FREQUENCY RANGE
There are several frequency ranges for wireless intercom systems and other wireless products. Here we use the frequency range from103-108MHz.
The frequency that will work best for an application depends on the wireless devices already in use not only in the building itself, but also in surrounding buildings. For instance, if a residence is using wireless networking which operates in the 2.4GHz range, a wireless intercom that operates in this range may interfere with the network or vice versa. Ideally the best intercom for an application would be one that is in a frequency not in use in the surrounding area, or one that uses digital spread spectrum to reduce possiblity of interference.
CHOOSING A WIRELESS INTERCOM SYSTEM
There are two major benefits of a wireless intercom system over a traditional wired intercom. The first is that installation is much easier since no wires have to be run between intercom units. The second is that you can easily move the units any time.
With a wireless intercom system, you can be up and running minutes after you take them out of the box and power them up.
But with that ease of installation and convenience also comes some risk. There is risk of interference from other wireless and electrical devices. Other wireless devices near the intercom such as cordless telephones, wireless data networks, and remote audio speakers can interfere. Electrical devices such as motors can also cause noise.
There is also risk of other people hearing your conversations by picking up your conversation on a scanner, baby monitor, cordless phone, or a similar device on the same frequency. However, there are wireless intercoms that reduce or eliminate both of these risks.
MICROCONTROLLER…………
TRASMITTER
A transmitter is an electronic device which, usually with the aid of an antenna, propagates anelectromagnetic signal such as radio, television, or other telecommunications
In radio electronics and broadcasting, a transmitter usually has apower supply, an oscillator, a modulator, and amplifiers for audio frequency (AF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto thecarrier frequency, which is then broadcast. Generally and incommunication and information processing, a transmitter is any object (source) which sends information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a transmitter. Most devices on the market typically have a short range of up to 30 feet (9 metres) with any average radio (up to about 75 feet (23 metres) with a very good radio under perfect conditions) and can broadcast on any FMfrequency from 76.0 to 108.0 MHz
FM transmitters are usually battery driven, but some use thecigarette lighter socket in cars, or draw their power from the device itself.
LIMITATIONS
• The relatively low power output of FM transimitters sometimes makes it unsuitable for use in some large urban areas because of the number of other radio signals. This is compounded by the fact that strong FM signals can bleed over into neighboring frequencies making the frequencies unusable with the transmitter.
Specification: 4-channel, Modulation mode range 50HZ - 15KHZ wide band High-clarity , full -stereo sound Synonym preference < - 60dB Power light and frequency LED indicator Size : (L) 88mm x (W) 42mm x (H) 20mm Color : white
DTMF
DTMF ENCODER
The DTMF encoder is an encoder is an 18 pin IC. Here we are using SH91214B.It generates high and low frequency according to the selection made.When we make a selection in the 4*3 matrix, it produces a multi-frequency signal.This signal is called dual tone multi frequency.A low frequency row and high frequency column represent each selection.Each row and column has its own specific frequency.When a particular selection is made,the corresponding row and column is activated and produces an output. The circuit contains RC network(R1,R2,R3,R4) and (C1,C2,C3).According to the time duration the encoder IC produces the generation.The IC contains filters and frequency dividing networks. These network generates separate frequency for rows and columns. We can convert this IC pulse configuration by changing the status of a particular pin.The Vcc of the IC ranges from 3V to 5V. We usually use a 3.3Vzener for giving Vcc.The output of the coder IC is in the digital form.
DTMF ENCODER CIRCUIT.
DTMF DECODER
The basic function of a decoder is to detect the presence of a specified combination of bits on its inputs and to indicate that presence by a specified output level.In its general form, a decoder has ‘n’input lines to handle ‘n’ bits and form one to 2^n output lines to indicate the presence of one or more n-bit combinations.
The DTMF decoder consists of an 18 pin IC HT9170B.This is a complete DTMF receiver designed to detect standard DTMF signals. It generates a combination of high and low frequency according to the selection status. It includes a differential input amplifier, filter section and decoder section and storing logic circuits.The differential input amplifier allows adjustment of gain and choice of input configuration. The filter section a dial tone filter for dial tone rejection and separates the dial tone signal into low group and high group tones.
Features
• Full DTMF receiver in 18-pin plastic packages.
• Single 5V power supply.
• Internal gain setting amplifier.
• Adjustable guard time
• Built in dial tone filter
• Uses inexpensive 3.58MHz crystal
• CMOS for low power consumption
• Tri state outputs
• Early steering outputs.