Analytic functions visualization buildings Talkback hands-free system

Analytic functions visualization buildings Talkback hands-free system


With the development of electronic communication technology, people's safety

awareness, building intercom products have already walked into thousands of

households, in intelligent
Residential areas have been widely applied, safe, comfortable, convenient

communication of service to the people. The intercom speaker system is composed of

a
A doorway machine and a plurality of indoor machine, system with its convenient

installation, simple operation, fashion modeling, close to life by the user
Popular. Because of the interference by hands free design background noise

influence is relatively large, and the band in the audio requirements.
Handle phone answering voice signal is different, according to the industry

standard GA/T678-2007 "network video intercom system technology
For "to the audio index display, calling the whole loudness rating channel value

is up to 21 ± 5dB, the whole response channel
The corresponding evaluation value is 18 ± 5dB. As a functional intercom hands-

free building intercom basic refers to the visitors can and households.
The double talk, voice clear, sonorous coherence requirements, without distortion

and self. The effect of the building intercom intercom hands-free system
The proposed quasi duplex audio circuit design between full and half duplex

design, can effectively eliminate the full duplex intercom
Howling phenomenon appears in the process, improve the intercommunication effect,

and the ratio of digital full duplex intercom audio processing cost is low.
One, building intercom several audio processing mode
Most of the market building intercom manufacturers of communication using RS-485

bus balance transmission mode, network topology by using the terminal.
Bus type structure, characterized in that RS-485 can support multiple nodes, long

distance transmission, high transmission rate, the equilibrium.
Actuator and a poor combination of the receiver, the ability of anti common mode

interference enhancement, noise interference is good, can realize the two-way

intercom function
Sure. At present, several audio processing estate intercom system used by the

main:
The full duplex mode intercom
Send and receive the data transmitted by the transmission line shunt, are two

different, both sides of communication can be made at the same time.
Send and receive operations. Switch full duplex mode without direction, did not

produce the switching time delay, building intercom
System doorway machine and the indoor machine can realize simultaneous two-way

intercom and clear voice. But the disadvantage is the voice of the limited size,

volume
The sound feedback howling phenomenon, influenced by the words sound effects.
In half duplex mode intercom
Intercom chip 34018 or 34118 door machine and the indoor machine. Using the same

transmission line as both receiving and sending
Send, although the data can be transmitted in two directions, but both sides of

communication can not send and receive data. In half duplex mode, through
The transmitter and receiver each end of the credit system, the send / receive

switch connected to the communication line, switch directions, so half
Duplex talkback effect sound big, but there are sound transmission delay

phenomenon obviously, and the higher chip integration, sound
If no discrete device has good effect, so the speech distortion situation.
Use of digital audio processing technology
Use of digital audio processing technology, with noise elimination and howling

suppression function, can realize the high clear video communication
Intercom, doorway machine and the indoor machine at the same time, intercom and

clear voice, more for IP building intercom system of digital network transmission,

the
Advantages of audio is clear and smooth, free from outside interference of

electromagnetic wave, the transmission distance of unlimited extension, the local

network can realize the
Speak; disadvantage is the high cost of intercom equipment, apply only to the

connection and affordability with network transmission of high-end users.
Two, design principle
Quasi duplex talkback method this paper describes the three methods are different,

it has the advantages of low cost, large volume, voice clear
Clear advantages, the actual test results audio index full loudness rating can

reach 19.6dB, and overcomes the shortcomings of the traditional half duplex on
Speaking voice chip transmission delay phenomenon. The principle is described as

follows:
Full duplex mode intercom original door in the dialogue process machine MIC and

SPK with indoor machine MIC and SPK open at the same time,
This caused when the electroacoustic devices MIC and SPK sensitivity will cause

large feedback phenomenon leading to whistle, but this time as long as the
Four electroacoustic devices in a not to participate in the work feedback

interrupt, howling away. Therefore, this article is in full duplex on
Speaking circuit improves sensitivity four electroacoustic devices as possible, at

the same time in the audio transmission pathway in the doorway machine and the

indoor machine of each
Two different points (MIC a, SPK a) by impedance isolation, amplification, shaping

and CPU sampling, digital filtering,
Comparison, to confirm this in a working state is MIC or SPK, and is controlled by

the CPU automatic switching, effective party into the work
The state, in a closed state is invalid. Because the four electroacoustic devices

as long as one does not work will not cause howling phenomenon
Therefore, electroacoustic devices in practical intercom CPU only control gate

machine or indoor machine side (MIC and SPK) to switch to the.
Three, the quasi duplex design system.
Hands-free building intercom system including the doorway machine and a plurality

of indoor machine, which comprises a door door machine machine MIC transmission

channel and gate
SPK transmission channel, each of the indoor machine comprises an indoor machine

MIC transmission path and the indoor machine SPK transmission channel, or all the

room door machine
Within the machine also includes the CPU, the CPU and MIC transmission channel,

SPK transmission channel connection, and one closed control. MIC transmission
Channel, between SPK transmission pathway and CPU are sequentially connected with

the impedance isolating circuit, amplifying circuit and shaping circuit.
Four, the conclusion
Due to the quasi duplex intercom system design is based on the basis of the

original full duplex, so enter intercom state, pass
If one of the electroacoustic devices completely in the work of the state,

electroacoustic devices of the other party into the switching state, thus avoiding

the feedback.
Called the phenomenon occurred, and keep the original full duplex intercom voice

clear, without delay the advantages, and the volume of the sound to
Half duplex IC is also difficult to reach a height. In the case of both intercom,

also won't appear half duplex voice blocking chip
Plug phenomenon, but call where the sound which the effective process. The design

scheme has a cost advantage, in the next building intercom
Get more extensive application in the system.