A Microcomputer Based Recorder Hardware Design

Introduction In view of the current development trend of paperless recorders, this topic should overcome the following major difficulties: (1) universal input technology, (2) USB communication interface technology, (3) liquid crystal display technology, and (4) system reliability design. technology.
1 system hardware design
1.1 Requirements of hardware system design The hardware is the material basis for the real-time control of the paperless recorder measurement and control system. It runs under the coordination of the system software to realize the detection and storage of the on-site production process or the parameters of the controlled object, and indirectly complete the production process. Or the control task of the controlled object. To complete these tasks, it is impossible to achieve complex tasks by relying on a single MCU. It is necessary to have enough measurement and control interfaces. These measurement and control interfaces and configuration of measurement and control functions are closely related to measurement and control requirements and measurement and control objects. The degree of measurement and control interface function circuit configuration determines the technical performance of the application system. Increasing the configuration circuit according to the characteristics of the paperless recorder system is a key issue. In order to complete complex functional systems, the system must add peripherals including: external devices, sensors, and transmitters, power amplification and actuators, analog input channels, digital input and output channels, interface circuits, and system operation. power supply. In the system, it is necessary to design a microprocessor-centered main control board, which should have an interface for implementing program firmware, data storage, display input and output, and peripheral communication. [2] The peripheral channel switching control board is responsible for controlling the time-sharing and time-limited input of the 9 channel signals. The signal processing board – completes the signal amplification and reduction and controls all signal input voltages within the range of the A/D required input. The switching power supply is responsible for providing a stable, low-interference, digital and analog isolated power supply system to the system; the data output board is used to transmit data to the LCD display to display the desired image.
1.2 Design of the main control board The main control board is the soul of the whole system. The input and output of all control signals are received, processed and transmitted through it. [3] The design of the main control board is developed around the 80C196KC. According to the design task, the main control board needs to complete the reading of the A/D data, data storage, data calculation, current time tracking record; Control, according to the need to switch the information of the field analog signal to ensure that the analog signal is limited to enter the processing amplifier board; at the same time control the scanning board, responsible for the 9 channels of the signal into the signal processing amplifier board; also have a communication module The interface function also has a display interface and a memory card interface; for this purpose, the 80C196KC must be peripherally extended to have more I/O ports and larger storage space.
2 system main hardware circuit design
2.1 peripheral analog-to-digital conversion interface design
2.1.1 Universal Signal Input System Requirements There are many types of signals that can be collected and processed by this paperless recorder system. The system requires that any signal be input in each channel, and the system has only one common amplification. Processing board. Therefore, it is required that the signal enters and exits the channel through the switching current limit of the solid state relay, and the time occupied by the signal of each channel on the amplification processing board is as short as possible, which also requires that there is no large charge element on the processing board. In the AR series of paperless recorders, the system converts most of the filtering into program filtering and A/D acquisition chip processing, which requires good anti-interference performance in selecting the A/D chip.
2.1.2 Selection of integral type A/D in design The integral type A/D chip can meet the industrial field interference signal, so I chose the ICL7109 double integral A/D. The peripheral design of the A/D chip is shown in Figure 1:

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As shown in Figure 1, the ICL7109 has a 14-bit (12-bit data and one-bit, one-out) latch and a 14-bit three-state output register, which can be easily combined with various microprocessors. The device is connected directly without the need for an external extra latch. The system adopts the direct interface mode, and the MODE terminal of the ICL7109 is grounded, so that the 7109 works in the direct output mode. When the oscillator select terminal (ie, OS terminal, pin 24) is grounded, the 7109 clock oscillator operates as a crystal oscillator, and the internal clock is equal to the oscillator frequency divided by 58. The ICL7109 clock frequency selection must follow two principles: It is required to have a certain conversion time. In the paperless recorder, it is desirable that the conversion time of the AD be as fast as possible. Of course, it must be within the frequency range allowed by 7109. Another principle is to suppress the interference requirement, according to the frequency of the main interference source in the system. To select the clock frequency of the ICL7109, in order to suppress this interference signal, the duration of the integration phase is required to be an integer multiple of the interference signal period. Let the frequency of the interference signal be Ff, the period is TF, and the integration duration is 2048TCK=2048/FCK to suppress the interference of Ff.
Should take
F ck =2048F f /K
Where K=1, 2, 3, 4... The larger the K value is, the better the corresponding anti-interference effect is, but the required conversion period is lengthened. In this design, because the interference factor against 50HZ is to be completed, and 10 AD conversion results are to be completed in 1 minute, K=1 is taken. Then the required crystal value can be calculated.
F CK =2048×50/1 =102400HZ
Since there are in IC7109:
F CK =F OSC /58
Where FOSC is the frequency of the crystal. The calculation can obtain the required crystal frequency of 5.9392MHZ.
Integration time = 2048 × time period = 20ms, the same as the 50Hz power cycle. The integration time is an integer multiple of the power supply cycle, which suppresses 50Hz serial mode interference.
The voltage signal or the thermal resistance signal of the industrial site is converted and amplified, and has a positive signal and a negative signal. Therefore, INLO=0 in the design. In addition, the reference voltage is set to 2V through the voltage regulator circuit in the design, so that 7109 can be input. The analog range is: -2V to +2V, ie the maximum range is Fs=4V.

Generally, the value of Rint is such that the current flowing through the A/D in the de-integration phase is 20uA, and Rint=200KΩ. According to Equation 9, when the analog input signal is small, such as 0-0.5 volts, it is automatically zeroed. The capacitor can be doubled to the integral capacitor CINT to reduce noise. The larger the value of CAZ, the smaller the noise. If CINT is 0.15μF, then
CAZ = 2 CINT = 0.33 μF.
In this design circuit, the RUN/HOLD pin is connected to +5V to make the A/D conversion continuous. [4] When the A/D conversion is in progress, the STATUS pin outputs a high level, and when the STATUS pin falls low, the address signal A1 latched by the 74HC373 outputs a low level signal to the HBEN of the ICL7109, and reads the upper 4 bits. Data, polarity, and overflow bits; a low level signal is output from A0 to LBEN, reading the lower 8 bits of data. RUN/HOLD is connected to +5V, A/D conversion is continuously performed, and the A/D conversion strong signal is reversely connected to the interrupt input pin of 80C196KC. When the A/D conversion is completed, the interrupt signal is automatically applied, and then 80C196KC gives The chip select signal, the read signal, and the HBEN, LBEN signals, the results of the A/D conversion appear on the data buses D0 to D7 according to the control signals. This method simplifies the design without the need to acquire data without affecting the operation of the microprocessor.
2.2 Communication interface design RS485 communication interface is designed, and a dedicated USB communication module interface can be provided at the same time. As shown in Figure 2 below

Figure 2 Communication interface distribution control diagram The switching between RS485 communication and USB interface communication can be realized by the optical couple. [5] Here, the P1.4 of 80C196KC is used as the switching signal. When RS485 communication is required, P1 can be used. 4 Set to 1, otherwise set P1.4 to 0 to enable USB interface communication.
2.3 The design of the display module interface refers to the characteristics of the liquid crystal display using the paperless recorder in domestic and international markets. [6] By comparing and analyzing various liquid crystal data, a YD501A color liquid crystal VRAM color liquid crystal display was selected. The DC/DC voltage converter generates various driving voltages for the liquid crystal, the DC/AC inverter is used to illuminate the cold cathode backlight, the display driving logic circuit uses optimized logic circuits, and the time sharing technology is used for display and writing. The data is simultaneously performed, realizing high-speed updating of the screen, and does not interfere with each other. The basic principle of YD501A is shown in Figure 3 below:

Figure 3 LCD control block diagram
3. Conclusions Through all the routine experiments required by the standard, the results fully meet the various specifications of the paperless recorder standard, and can fully meet the needs of the industrial field use environment. Through experiments, it is proved that the technology proposed by this topic needs to be mastered and successfully applied in practice. And through the enhancement of signal acquisition, signal processing, and software/hardware design, the stability, reliability and advancement of the paperless recorder in the field are improved.
The author of this paper innovates: For industrial field interference signals based on 50HZ, the integration method is adopted to select a specific integration period to achieve the anti-interference effect of filtering.
[1] Xie Wei. Current Status and Development Trend of Paperless Recorder[J]. Automation and Instrumentation, 2001, (3): 24-25.
[2] Wang Jian. Principles and Application Technology of MCS-96 Series Microcontrollers [M]. Wuhan: Huazhong University of Science and Technology Press, 1999,
(01): 39-371.
[3] Zhou Ligong. Etc. PDIUSBD12 USB firmware programming and driver development [J], Electronic World, 2003, (2)
[4] Application of PDIUSBD12 chip in USB interface circuit [D]. China IC Network, 2005, (10).
[5] Ma Zhongmei. Design of C language application of single chip microcomputer [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2001,
(11): 15-18.
[6] Wu Zhengang, Chen Hu. PLC man-machine interface and programming [J]. Microcomputer Information, 2005, 8-1: 21-23.

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