The method and apparatus of duplex transmission vision signal and control data
One, technical field:
The invention belongs to the TV monitoring and controlling field, relate to the transmission and the video camera front-end control of analog video signal.
Two, background technology
In the TV monitor system, often need in the analog video signal of receiving front-end video camera output, need oppositely to transmit control data signal again to video camera, three variable lenses, The Cloud Terrace etc.These control data signal are if can then have certain value in actual applications with the vision signal duplex transmission in single coaxial cable.
The implementation method of single cable duplex transmission analog video signal and control data signal has multiple.Carry out reverse transfer beyond by modulation the frequency spectrum of data-signal being moved to the frequency video signal scope, receiving terminal adopts filter to leach its frequency component, carries out demodulation afterwards again and gets final product.But it is comparatively complicated that this method implements, and overall cost height, and because system's medium frequency complicated component during duplex transmission, system non-linear easily cause new distortion, bring harmful effect for the picture quality of the vision signal of forward transmitted.
Another kind of way is to adopt the high speed subtracter to isolate the control data of reverse transmission and the vision signal of forward transmitted respectively at vision signal transmitting terminal and receiving terminal, owing to be difficult to accomplish the separation fully of binary signal, therefore the data-signal that oppositely transmits still can bring interference to the video signal of forward transmission.
Owing to how not adopt in the deficiency of above-mentioned two kinds of schemes thereby the practical application, but except that adopting a coaxial cable transmission video signal, adopt a multicore cable uplink control signal in addition again.
Three, summary of the invention
The objective of the invention is: overcome the implementation method complexity of existing single cable duplex transmission analog video signal and control data signal and the difficulty of signal processing, or overcome existing two cables transmission video signals and oppositely transmit control signal respectively, cause the deficiency of the high and wiring complexity of construction cost.The objective of the invention is to utilize the reverse data signal of field blanking interval of vision signal, trace picture quality is not had influence, and the realization of method is easy to be reliable.
Technical scheme of the present invention comprises following several aspect:
1, the realization of impedance matching during duplex transmission.
As figure one, the vision signal transmitting terminal is connected on the input port of coaxial cable after three groups of circuit parallel connections are arranged, for guaranteeing impedance matching, must make three groups of circuit see outward that from cableport equiva lent impedance in the past is 75 ohm, make during design that the output impedance of video buffer and buffer circuit (14) is 83 ohm, direct current signal extracts and the input impedance of signal isolation circuit (12) is greater than 1K ohm, and control code is separated and the input impedance of level shifting circuit (15) is greater than 3K ohm.For the amplitude of guaranteeing coaxial cable input port vision signal is 1Vp-p, require the multiplication factor of video buffer and buffer circuit (14) to be larger than 2 times.
The vision signal receiving terminal is connected on the output port of coaxial cable after three groups of circuit parallel connections are arranged, and is equiva lent impedance and the coaxial cable coupling guarantee three groups of circuit, makes the output resistance of DC stacked and buffer circuit (01) greater than 1K ohm during design.Control code supercircuit (04) is operated on off state, for almost opening a way, just works when field blanking interval has the signal of transmission during the trace of field.The input impedance equivalent resistance that exchanges after stopping direct current and impedance matching circuit (06) and video buffer and buffer circuit (18) parallel connection is 81 ohm, makes from the look-out equivalent resistance of the right output port of coaxial cable to be 75 ohm.Thereby realize the coupling of impedance at the vision signal receiving terminal.
2, the transmission of control code and acceptance
The transmission of control code is the reverse data signal of field blanking interval of utilizing vision signal with accepting, be the vision signal transmitting terminal when the sending vision signal also receiving video signals receiving terminal reverse transfer data pulse signal of coming, this signal send the decoding circuit decoding of being made up of single-chip microcomputer (MCU) (17) after control code separation and level conversion (15), restore original control information.
The video reception end determines oppositely to send the length of Frame according to the ultimate range of transmission cable.Amount of delay and transmission range by the coaxial cable unit length are determined one-way transmission amount of delay (Δ T), for not row, the field system chronizing impulse of interference video sending and receiving end, and consider separated in synchronization and software responses time, the time span that actual every row can transmit data is determined by following formula:
2X one-way transmission amount of delay (Δ T)+Frame time span+separated in synchronization and software processes time≤64 microsecond.
One-way transmission amount of delay (Δ T) is directly proportional with transmission cable length, and data that the long more then every frame of cable can send out that hence one can see that are just few more.Generally being no more than 400-600M with cable length during the analog video signal transmission and being advisable, is that the 20-26 microsecond is more appropriate so extrapolate the time span of the each frame control data that sends of the present invention.This length can satisfy the needs of general TV monitor system, need be by means of the technology of two-way relaying when cable is long.
During transmission, the single-chip microcomputer of data sending terminal (MCU) (08) will enter the control data router after receiving keyboard input control order (10).This program at first to being monitored by the field sync signal of vision signal synchronizing separator circuit (07) output, after monitoring field sync signal, begins the row of field blanking interval is counted synchronously, to determine being which row that is in field blanking interval at present.When entering the 9th row of field blanking interval, this row latent period one finishes, single-chip microcomputer (MCU) (08) just will be to be sent a frame control data deliver to code stream translation circuit (05), control code supercircuit (04), control data directly is superimposed upon in the active line of any delegation in the 9th to two Ariadne after the field blanking interval field synchronization or several row and sends, through the coaxial cable reverse transfer.
During decoding, the control code of data receiving terminal is separated with level shifting circuit (15) the advanced row buffering of the vision signal that is superimposed with the control data pulse is isolated, then the synchronizing signal in the vision signal is clamped on the same DC level, again by voltage comparator after with clamp signal and the level value determined of decision threshold level setting (19) relatively, control code is separated with level shifting circuit (15) and will be separated the voltage signal that exceeds decision threshold level, and this wherein just has the pulse signal of control data sign indicating number; During decoding, the single-chip microcomputer of data receiving terminal (MCU) (17) is to being monitored by the field sync signal of vision signal synchronizing separator circuit (16) output, after monitoring field sync signal, which begin the row of field blanking interval is counted synchronously, to determine the being row that is in field blanking interval at present.When entering the 9th row of field blanking interval, this row latent period one finishes, single-chip microcomputer (MCU) (17) just reads by control code and separates a frame control data signal of exporting with level shifting circuit (15), and produces control signal corresponding output behind relevant program analysis.
3, the transmission of direct current signal and acceptance
The reverse process of transmitting of direct current signal is, the single-chip microcomputer of data sending terminal (MCU) (08) writes signal to be sent data latches (03), sends into coaxial cable behind level conversion (02), DC stacked and buffer circuit (01) after receiving keyboard input control order (10).
When direct current signal is accepted, extract the direct current signal that from coaxial cable, extracts reverse transmission with Signal Spacing (12) by dc control signal, and available this signal directly drives the device such as types such as miniature relay, photo-coupled relays.
Characteristics of the present invention are: utilize the reverse data signal of field blanking interval of vision signal, trace picture quality is not had influence, and the realization of method is easy to be reliable.The application of device is convenient, and cost is low, and the relative time delay of solution data back transmission produces the problem of error code in the time of may causing the control data sign indicating number to separate.
Four, description of drawings
Fig. 1 is the method block diagram of base band duplex transmission vision signal of the present invention and control data;
Fig. 2 is a concrete enforcement circuit block diagram of the present invention
Fig. 3 adopts specific embodiments of the present invention: a kind of 8 * 4 supervisory control system control/switchs and front end decoder
Five, specific embodiments: a kind of 8 * 4 supervisory control system control/switchs and front end decoder
Be example with a kind of 8 * 4 supervisory control system control/switchs and the front end decoder that adopts this invention fabrication techniques below, the embodiment of this technology is described.
1, circuit structure design explanation (with reference to figure 2)
Instance system is formed (see figure 3) by one " 8 * 4 supervisory control system control/switch " (claim not only main control computer) and one to eight " front end decoder " (but also claiming decoder) and video camera and monitoring television.
Main control computer is accepted multi-channel video signal, and can be oppositely to wherein electric power starting, camera lens and the The Cloud Terrace state of any No. one video camera are controlled.
Adopting AT89C51 single-chip microcomputer (08) in the main control computer is control chip, and with memory under program (E
2ROM), this control system of circuit primordial (MCU) such as address latch.DC stacked and buffer circuit (01) adopt the low pass circuit of being made up of resistance, inductance and electric capacity, and its impedance of seeing into from the coaxial electrical cable-end is greater than 1K ohm, thereby play the isolation vision signal, transmit the purpose of flip-flop.Level shifting circuit (02) is made up of open-collector gate circuit and PNP triode, realizes the conversion of Transistor-Transistor Logic level to 12V voltage, and has the fan-out capability of 5MA electric current.Data latching (03) is made up of the 8D latch, is used for the data of AT89C51 single-chip microcomputer (08) output are maintained.Control code supercircuit (04) is a kind of switching circuit, is subjected to the control of the serial data pulse signal of code stream conversion (05) circuit output, and a forward stroke interval does not have influence for disconnecting to the work of circuit.Field blanking interval is subjected to the control of the serial data pulse signal level of code stream conversion (05) circuit output, and the amplitude of data-signal with≤0.7Vp-p is superimposed upon on the vision signal, realizes reverse transfer.Code stream conversion (05) is 16 shift registers of incorporating into to go here and there out, is used for sending the data-signal of depositing at a frame time internal shift.Stopping direct current and impedance matching (06) mainly are made up of electrochemical capacitor and resistance, are used to realize exchange the coupling of video impedance and every the flip-flop of going to be sent with buffer circuit (01) by DC stacked.Video buffer and buffer circuit (18) are the video amplifier of a high input impedance low output impedance, are used for vision signal is amplified the television set that rear drive monitors usefulness.Vision signal synchronizing separator circuit (07) adopts the LM1881 application-specific integrated circuit (ASIC) to realize the separation of row, field sync signal.The row of separating, field sync signal insert AT89C51 single-chip microcomputer (08) with interrupt mode, thus the accurate timing when guaranteeing to send data.Operating state demonstration (09) is made up of one group of light-emitting diode, data latches, driving triode, is used to show the information and the work at present state of input.Control command input (10) is a key circuit, is used for input information.Fault alarm (11) is a buzzer and drive circuit thereof, and the abnormal problem that is used for system work process is occurred in time sends sound prompting.
The AC power of front end decoder is subjected to the control of the direct current signal that main control computer sends.During operate as normal, the limit sends the control data that the vision signal edge joint is sent by main control computer, and according to the coding of these data different controlling object is carried out control corresponding.
Dc control signal in the front end decoder extracts with signal isolation circuit (12) and can adopt and the DC stacked and identical circuit of buffer circuit (01), and its function is also identical.Power supply control (13) can be adopted high-sensitive relay or photo-coupled relay for the device of control front-end processor mains switch, and what adopt here is that model is the photo-coupled relay of GTJ2-2A.Video buffer and buffer circuit (14) can adopt the video amplifier of high input impedance low output impedance, and its effect is that vision signal is amplified the rear drive coaxial cable.It is the split circuit of the voltage comparator of LM393 as the control data pulse that the control code separation can be adopted model with level shifting circuit, for guaranteeing the precision of Signal Separation, reduce error code, need carry out clamp to the lock-out pulse of vision signal, to keep the unanimity of its black level, by decision threshold level circuit (19) is set then its thresholding reference potential accurately is set.Decision threshold level is provided with circuit (19) and can adopts multiturn potentiometer that the voltage of high stable is carried out dividing potential drop to realize.Vision signal synchronizing separator circuit (16) in the front end decoder is identical with (07) circuit structure and effect in the main control computer.Single Chip Microcomputer (SCM) system also adopts AT89C51 single-chip microcomputer (17) to be control and decoding chip, and the row of separating, field sync signal insert single-chip microcomputer (17) by interrupt mode, thus the accurate timing when guaranteeing to accept data.
2, operation principle explanation (with reference to figure 2)
During " 8 * 4 matrix handover control system " work, at first require to open the power supply of certain front-end processor by control command input (10), after video receiving terminal Single Chip Microcomputer (SCM) system (MCU) (08) responds this instruction, in data latching (03), write the control corresponding word by its data and control bus, through level conversion (02), DC stacked and isolate (01), coaxial cable reverse transfer coaxial cable port to the respective front ends machine.Again through dc control signal extract go out wherein DC control electric current with Signal Spacing (12) circuit extraction after, photo-coupled relay conducting in the driving power control (13), make this front-end processor power, video camera is started working and outputting video signal, this signal is transferred to the main control computer end through video buffer and buffer circuit (14), coaxial cable, sends into monitoring television through stopping direct current and impedance matching (06), video buffer and isolation (18) circuit again and demonstrates image.
When operating personnel send other controls when requiring by control command input (10), after video receiving terminal Single Chip Microcomputer (SCM) system (MCU) (08) responds this instruction, portion is ready to the control corresponding data within it, but do not send immediately, but field system chronizing impulse sends interruption by the time, and after calculating the sync break of field blanking interval the 9th row, just go here and there out incorporating in code stream conversion (05) circuit and write the control corresponding data in the shift register, thereby send the data-signal of depositing at a frame time internal shift by its data and control bus.These data pulse signals are superimposed upon field blanking interval the 9th and walk on the 24 row vision signal active lines, through the coaxial cable reverse transfer.
After the control wave of reverse transfer arrives front end, separate and the clamp of level conversion (15) circuit, and isolate the control data pulse that main control end is sent after comparing in voltage comparator with decision threshold level vision signal through control code.These signals are delivered to Single Chip Microcomputer (SCM) system (MCU) (17) with other signals of separating.After Single Chip Microcomputer (SCM) system (MCU) (17) sync break only on the scene, just open the synchronous interruption of row, and begin counting.The 9th row in counting to field blanking the time begins the signal imported on the image data mouth, and these signals are decoded, and confirms its control requirement then, sends control command to the control corresponding object again according to this requirement.