Design of temperature control system for high-precision biochemical analyzer based on ARM9

　　Embedded Linux is an embedded operating system based on Linux. It is widely used in mobile phones, personal digital assistants (PDAs), media players, consumer electronics , and aerospace. The advantages of Linux in embedded systems are: first, Linux is open source, there is no black box technology, and many Linux enthusiasts around the world are strong technical support for Linux developers; second, Linux kernel is small, efficient, and the kernel is updated very quickly. Linux can be customized, and its minimum system kernel is only about 134KB. Third, Linux is a free OS and is very competitive in price. Linux also has many features required by embedded operating systems, and the most prominent one is that Linux is suitable for a variety of CPUs and a variety of hardware platforms. It is a cross-platform system. So far, it can support 20 to 30 CPUs. The porting speed is much faster than the Java development environment. At the same time, the structure of the Linux kernel is very complete in terms of network. Linux has the most complete support for the most commonly used TCP/IP protocol in the network. It provides support for 10M, 100M, and 1G Ethernet networks, as well as wireless networks, Toker rings, optical fibers, and even satellites.

　　1 Introduction

　　ARM9 is increasingly widely used in various bioelectronic instruments, and fully automatic biochemical analyzers are a typical application. Temperature has a great influence on the test results during the detection and analysis process of the biochemical analyzer. The reliability of the biochemical test results can only be guaranteed when the samples and reagents are tested at the specified temperature. This system uses the ARM9 processor as the core of the control system to implement the fuzzy self-tuning PID control algorithm. After testing, the system has high accuracy, good stability, and fast response. The temperature of the reaction disk is controlled at the current standard detection temperature of 37°C, the temperature control accuracy is ±0.1°C, and the display accuracy is ±0.01°C, which fully meets the requirements of clinical use.

　　TI's OMAP730 is the latest wireless communication baseband signal processor. The processor is an integration of TI's GPRS Class 12 communication module and the ARM926 general-purpose processor (GPP) dedicated to application processing. Since the speed of GPP can reach 200MHz, OMAP730 has twice the application processing performance of the previous generation OMAP710 processor. Like all OMAP processors, OMAP730 can support leading mobile operating systems, including Microsoft's smart phones and Pocket PC PhoneEdition, Svmbian OS and Series 60, Palm OS and Linux.

　　2 System Overall Design and Main Hardware Implementation

　　2.1 Overall system design

　　The system structure is shown in Figure 1. The system mainly consists of three parts: temperature measuring device, ARM controller and display transmission unit. The ARM controller adopts Samsung's S3C2410A. The temperature measuring device is responsible for temperature collection, which is composed of DS1 8B20 temperature sensor in this system. The whole system working process is to set the temperature value by the keyboard first, and the ARM controller controls the temperature sensor to collect the temperature signal. After the fuzzy PID control module calculates, the PWM wave is output to control the power drive module to realize the heating and cooling control of the temperature, and the temperature is displayed on the LCD at the same time.

　　2.2 Controller S3C2410

　　The S3C2410 processor is a 32-bit microcontroller produced by Samsung based on the ARM920T processor core of ARM and manufactured using a 0.18um process. The processor has: independent 16KB instruction cache and 16KB data cache, MMU, LCD controller supporting TFT, NAND flash controller, 3-way UART, 4-way DMA, 4-way Timer with PWM, I/O port, RTC, 8-way 10-bit ADC, Touch Screen interface, IIC-BUS interface, IIS-BUS interface, 2 USB hosts, 1 USB device, SD host and MMC interface, 2-way SPI. The S3C2410 processor can run at up to 203MHz.

　　S3C2410A is a low-power, highly integrated ARM920T core 16/32RISC embedded processor designed by Samsung Electronics Co., Ltd for handheld devices. It runs at a frequency of up to 203MHz, has independent 16k instruction and 16kB data caches, an MMU unit for virtual memory management, an LCD controller (STN&TFT), a boot unit system manager for non-linear (NAND) FLASH, a 3-channel asynchronous serial port (UART), input and output ports, a real-time clock unit (RTC), an 8-channel 10-bit ADC with a touch screen interface, an IIC bus interface, an IIS bus interface, a USB host unit, a USB device interface, a 2-channel SPI interface and a phase-locked loop (PLL) clock generation unit.

　　This system design adopts 32-bit RISC embedded processor working mode and NAND FLASH boot mode. The NAND FLASH memory expansion selects K9F1208 produced by Samsung Electronics, with a single chip capacity of 64MX 8bit (64M bytes), an operating voltage of 2.7~3.6V, an 8-bit data width, hardware data protection function, and support for power-on automatic boot function. According to system requirements and to give full play to the data processing capabilities of the 32-bit CPU, this system uses two HY57V561620Ts in parallel to build a 32-bit SDRAM memory system, with a total of 64MB of SDRAM space, which can meet the requirements of embedded operating systems and various relatively complex functional operations. [page]

　　2.3 Implementation of temperature acquisition unit

　　The temperature acquisition unit mainly samples the temperature signal in real time and responds to the host's command [31. The temperature sensor of this system uses DS18B20. DS18B28B20 is a single bus temperature sensor launched by the American semiconductor company DALLAS. The device has many advantages such as small size, simple structure, wide practical voltage, networking, low cost, easy bus expansion and maintenance, and has control circuits, transceiver circuits and storage circuits. DS18B20 has a wide voltage application range (3~5.5V) and can realize 9~12-bit digital conversion of temperature signals through programming, with a maximum resolution of 0.0625℃. Its measurement temperature range is -55~+125℃, among which, within the range of -10~+85℃, the accuracy can reach ±0.5℃. Since DS18B20 transmits data through a data line, the entire system must strictly work according to the timing specified by the single bus protocol of the device, so DS18B20 has a strict communication protocol to ensure the correctness and integrity of each data transmission. According to the communication protocol of DS18B20, when the host controls DS18B20 to complete temperature conversion, it first resets DS18B20 before each reading and writing. After the reset is successful, it sends a ROM instruction, and then sends a RAM instruction, so that the DS18B20 can perform the predetermined operation. The ROM operation command is mainly the operation of the sensor address. The RAM instruction mainly completes the temperature measurement, mainly including the operations of reading registers, writing registers, temperature conversion, etc.

　　2.4 Keyboard and LCD display unit

　　The system uses the keyboard control chip ZLG 728 with SPI interface to connect with the SPI interface of $3C2410A. The row lines R[2:0] and column lines C[7:0] scanned by ZLG7289 form a matrix keyboard. At the same time, the tasks of scanning, decoding, and de-jittering can be automatically completed inside the chip.

　　SPI (Serial Peripheral Interface) bus system is a synchronous serial peripheral interface, which enables MCU to communicate with various peripheral devices in serial mode to exchange information. SPI has three registers: control register SPCR, status register SPSR, data register SPDR. Peripheral settings include FLASHRAM, network controller, LCD display driver, A/D converter and MCU, etc. SPI bus system can directly interface with a variety of standard peripheral devices produced by various manufacturers. The interface generally uses 4 lines: serial clock line (SCLK), host input/slave output data line MISO, host output/slave input data line MOSI and low-level effective slave select line SS (some SPI interface chips have interrupt signal line INT, and some SPI interface chips do not have host output/slave input data line MOSI).

　　The full name of SPI interface is "Serial Peripheral Interface", which is first defined by Motorola on its MC68HCXX series processors. SPI interface is mainly used in EEPROM, FLASH, real-time clock, AD converter, and between digital signal processor and digital signal decoder.

　　The SPI interface is a synchronous serial data transmission between the CPU and peripheral low-speed devices. Under the shift pulse of the master device, data is transmitted bit by bit, with the high bit first and the low bit last. It is full-duplex communication. The data transmission speed is generally faster than the I2C bus, and the speed can reach several Mbps.

　　S3C2410A has an integrated LCD controller, so it can easily control various types of LCD screens, such as STN and TFT screens. The system uses Samsung 3.5 reflective TFT LCD LTS350Q1, 320 X 240 pixels, 256k colors, White LED backlight, and a built-in four-wire touch screen, which can be directly connected to the touch screen driver circuit of S3C2410A. The touch position can be directly sampled by the ADC circuit built into the CPU.

　　The keyboard and LCD connection diagram is shown in Figure 2.

　　3 Design of fuzzy self-tuning PID control algorithm module

　　The fuzzy self-tuning PID control system can detect and analyze uncertain conditions, parameters, delays, interferences and other factors during the control process, and use fuzzy reasoning to achieve online self-tuning of the three PID parameters, f and . The fuzzy self-tuning PID control not only maintains the characteristics of the conventional PID control system, such as simple principle, easy use, and strong robustness, but also has greater flexibility, adaptability, and accuracy.

　　The fuzzy self-tuning PID controller is based on the conventional PID controller to establish parameters K, K, K and the absolute value of the deviation IE I and the deviation change rate.

　　The absolute value of the IEcI is a binary continuous function relationship of the controller. The binary function relationship is]: = (, J j), = 0, J), K = (JEc}). The fuzzy self-tuning PID controller can adjust K, K and Kd online according to different IEcI.

　　The input deviation, deviation change rate and output membership function are shown in Figure 3 respectively.

　　For the membership degree in FIG3, when n=p, a and b are respectively 0.3 and 0.3; when n=i, a and b are respectively 0.06 and 0.06; when n=d, a and b are respectively 3 and 3.

　　The fuzzy-PID control system is a two-input three-output system. The input is the deviation E and the deviation change rate EC, and the output is the PID parameters K and. Seven different fuzzy language variables are used for description: negative small (NS), negative middle (NM), negative 3v (NB), zero (Z), positive small (Ps), positive middle (PM), positive large (PB). The control rule is: if E and EC then K, K, According to the basic principle of PID control and combined with practical experience, the fuzzy control table is designed as shown in Table 1.

　　4 System Software Design

　　The software part adopts the embedded Linux operating system, and the main process of the system is shown in Figure 4. The system is powered on to start the BootLoader, initialize the system hardware, load the operating system, and bring the system into a suitable environment. After the system boot loading is completed, a series of new threads are created, including the temperature data acquisition thread, the fuzzy self-tuning control algorithm thread, and the output thread, and the communication pipeline FIFO between the new threads is created. Whether to stop sampling can be controlled by the keyboard and external interrupts. If sampling is stopped, the threads are merged and the application is terminated.

　　The centroid method is used to defuzzify , and obtained from the fuzzy control rule table to obtain accurate values, and then these values ​​are substituted into the following formula:

　　5 Conclusion

　　This system uses the high-performance ARM9 series processor S3C2420 and the embedded Linux operating system. The temperature sensor uses the most popular single-bus temperature sensor DS18B20. A high-precision temperature controller in the biochemical analyzer is designed and implemented. The results show that the system can well control the temperature of the biochemical analyzer reaction pool within the required range, thereby effectively improving the detection precision and accuracy of the biochemical analyzer.

References:

[1]. S3C2410A datasheet http://www.dzsc.com/datasheet/S3C2410A_589565.html.
[2]. ARM920T datasheet http://www.dzsc.com/datasheet/ARM920T_139814.html.
[3]. Device datasheet http://www.dzsc.com/datasheet/Device_1397784.html.
[4]. DS18B20 datasheet http://www.dzsc.com/datasheet/DS18B20+_819975.html.
[5]. ROM datasheet http:// www.dzsc.com/datasheet/ROM_1188413.html.
[6]. ZLG7289 datasheet http://www.dzsc.com/datasheet/ZLG7289_1134608.html.