This article refers to the address: http://
Abstract: AIT2139 is a monolithic, crystal controlled, all digital video signal processor. Based on the introduction of video conversion chip AIT2139, the paper gives the principle and implementation method of designing VGA-TV video converter.Keywords : VGA-TV; video converter; AIT2139; multimedia teaching
1 Introduction
In modern teaching, especially in the process of higher education, multimedia teaching has gradually become a popular teaching method because of its strong interactivity, high efficiency and flexibility.
In order to facilitate the development of multimedia teaching, the author selected AIT2139 video conversion chip to design a VGA-TV video converter. The converter converts the computer's VGA signal into a broadcast quality NTSC or PAL video signal for output to a large-screen TV, thereby enabling auxiliary functions such as freeze, zoom and pan. At the same time, its video signal can also be output to the computer display through the interface provided by the converter.
2 AIT2139 chip introduction
The AIT2139 is a single-chip, crystal-controlled, all-digital video signal processor that supports multiple input formats (eg 640×480, 85 Hz, 800×600, 85 Hz, 1024×768, 60 Hz, etc.). AIT2139 has 3-channel, 8-Bit ADC input and 16.7M color conversion function; it has a dedicated storage compression circuit inside, external EDO?256k×16Bit? memory interface and SDRAM?1M ×16Bit? memory interface; AIT2139 control mode Simple, it can be controlled by HOST interface or I2 C bus. The chip automatically detects the input mode and the current TV mode. The output format can be selected from compositing, S-Video, YCbCr or RGB/SCART; all video processing can be done in the digital domain, eliminating the need for conversion circuitry. The digital encoder uses oversampling and is filtered with the AITech algorithm to output high quality NTSC and PAL signals. The internal functional block diagram of the AIT2139 chip is shown in Figure 1.
3 system working principle
The VGA-TV video converter is mainly composed of three parts: video conversion, video conversion control and remote control. Its system structure is shown in Figure 2.
The core of the VGA-TV video converter is the video signal conversion and video conversion control part. Therefore, the core of the design is the processing of the video signal and the control of the video conversion chip. I use AIT2139 video signal processor, and with a mature peripheral circuit designed a video signal conversion circuit to complete the video front-end processing and signal conversion; at the same time with eight-bit microcontroller EM78P156EP as the core, coupled with keyboard detection, I2C Circuits such as communication and remote control receive the conversion control part. The system is a typical analog-digital hybrid system. The power quality has a great influence on the output of the video signal. For this reason, a separate power supply card is used in the design and embedded in the system in the form of a backplane, thus achieving good results. .
4 system design
4.1 Video conversion part design
The main function of the video conversion part as the core of the system is to convert the RGB signal output by the computer into the standard input signal of the TV. The RGB amplified signal of the video front end is processed by the gate circuit, sent to the AIT2139 for conversion, and outputs two types of television signals: one is a full TV signal obtained by conversion, frequency selection and filtering, and the other is luminance and chrominance separation. TV signal, that is, the S terminal signal. Therefore, the RGB signals output by the computer can be directly connected to the computer display through coupling, buffering, and amplification, so that the operator can conveniently monitor the screen. For the full TV signal output, a complete frequency selection and filtering circuit is added to increase the stability of the TV signal. Figure 3 is a block diagram of a video conversion portion circuit.
(1) Video front-end processing
The input uses the three 8-bit A/D converters of the AIT2139 to perform A/D conversion on each channel of the R, G, and B signals at a sampling rate of 48 MHz. Its horizontal sync (HSYNC) and vertical sync (VSYNC) are buffered by the Schmitt trigger gate. The AD conversion of the AIT2139 is quite flexible, and the internal AD conversion reference voltage can be set by itself. The RGB signal in this design has a level range of 0 to 0.85V, and the given external reference voltage is Vk. It should be noted that Vk must not be lower than the maximum value of the RGB signal level.
Digital video processing can be performed using the YUV color component. Therefore, the RGB-YUV matrix in the AIT2139 chip can be used to convert the input RGB signal into a 4:2:2 format YUV component signal, and each component outputs 8 bits, and the total output signal. Works on 24 bits on the data bus. The actual design found that the YUV output flickers large. To this end, the author uses the finite impulse response digital filter constructed by the chip's internal AITech algorithm, which effectively reduces the output flicker.
(2) Working mode setting
The AIT2139 has two modes of operation, master mode and slave mode. This design selects the main mode. The AIT2139 generates all clock and sync signals and provides horizontal sync, vertical sync, and internal pixel data clocks to external memory devices. External multiplexed inputs, FIFOs, and memory will strictly follow these clock and synchronization information provided by the AIT2139. It has been found in the design that the data read in time of the VGA may not be synchronized with the write clock of the processor.
(3) Digital video coding
The core of AIT2139 is its processor part, which is mainly used to read and encode YUV digital video data in 4:2:2 format from an external storage device. Because the input signal is divided into luminance and chrominance components, the chrominance signal will be modulated by the composite digital subcarrier. The luminance component and the chrominance component signal are respectively interpolated to twice the pixel rate, and converted into an analog S-video signal by two 10-bit D/A converters, and the analog composite video signal is passed through the third channel 10 After the -bit converter output, the format control pin of the AIT2139 processor can be adjusted to select different clock parameters, thereby setting the output of the video converter to TV standard signals such as NTSC and PAL.
4.2 Design of video conversion control part
The VGA-TV converter main control board is the main part that controls the video conversion part. The board not only provides power for video conversion, but also sends operational control signals. The core of the main control board is the eight-bit single-chip EM78P156EP, which is equipped with keyboard detection, I2C communication, remote control reception and other circuits to form the conversion control part. The principle block diagram of the main control board is shown in Figure 4. The flow of its control decoding subroutine is shown in Figure 5.
5 Conclusion
Prolonged use by some colleges and universities: The VGA-TV video converter has stable performance and good effect, and can well assist modern multimedia teaching, so it has broad application prospects.
Wood Grain, Unique and Compact Design: This Aroma Diffuser is coated with wood grain, which makes it look very natural and primitive. With compact and portable design, the cap of the aroma diffuser is easy to take off, you won`t bother to unscrew the cap with great force when your hands is wet. Just gently take off the cap, add water and essential oil, enjoy high-quality life.
Portable with Adjustable Mist Output: Essential Oil Diffuser hold up to 200ml of water, not too big, not too small. It produce up to 35-70ml of moisture per hour. It can run up to 5.5 hours of continuous output in low mist. Automatic power off when water used up, which ensures safety. A long press to switch between high and low mist to extend the duration of misting. (One beep for high mist mode, two beeps for low mist mode)
7 Color LED Lights. 7 colors rotating through / Fixed one color steady on / Lights off. Each color is adjustable between bright and dim. A perfect nightlight for a kid's bedroom and soft light creates romantic atmosphere which helps you escape the hustle and bustle of modern life.
4 Timer Settings and Auto Shut off: 4 time setting modes: 1H/ 3H/ 6H/ ON/OFF. Diffuser automatically powers off when water level is too low.
Mulfunctional: Aromatherapy Diffuser adopts ultrasonic technology, this diffuser is extremely quiet when working. It gives out ultra fine and smooth mist which can soften and moisten dry and chapped skin in winter. It also helps you breathe better when your are sleeping with air conditioner on.
Home Humidifier,House Humidifier,Home Evaporative Humidifier,Home Warm Mist Humidifier
Shenzhen Hygea Technology Co.,Ltd , http://www.hygeaaromadiffuser.com