Design And Implementation Of Visual Intercom System For Buildings

Conventional visual intercom systems use digital encoding and decoding technology to directly transmit baseband signals.However,there are several drawbacks existing in the conventional systems.Firstly,the signals are susceptible to interference or distortion.Secondly,the stability of data communication is poor.Thirdly,there are many connection lines,complex wiring,and network distribution difficulties.If the systems use wireless communication technology,they are poor stabile or are incompatible with the reconstruction project of the old buildings already equipped with voice intercom.In order to solve the above problems,a hardware system for modulation and demodulation of audio and video,data transmission,frequency division multiplexing,system power supply and MCU control is designed by applying the technical schemes including carrier modulation and demodulation,and frequency division multiplexing.A two-way carrier amplifier and a feeding based system user distributor are designed.A software control system and its function design are also carried out,and the circuit-board-level design of the whole machine is completed,and several measures have been taken to improve integrity of the signal.Long-distance,bi-directional transmission and distribution of carrier signals such as power supply,video image,intercom voice,control data,etc.on a coaxial line or two-wire differential balance line are achieved on this system.In the test,the video transmission effect reaches the level for TV broadcast,and the image is transmitted in real time without frame loss and delay;The distortion of speech signal is less than3%,and its frequency range is 180 Hz to12k Hz,which can reach the quality level for FM broadcast;The signal frequency and duty cycle of the control data receiver are the same as that of the transmitter,and there is no error code in the transmission and testing process;All the control functions of the whole system can realize the communication and control tasks,and achieve the design goal of the system well.The whole system is stable and reliable.