Serial Communication Based on LabVIEW for the Development of an ECG Monitor

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Serial Communication Based on LabVIEW for the Development of an ECG Monitor Bing Yang 1,a, Yu Guo 2,b, Zhidong Wang 3,c and Yan Gao 4,d Faculty of Mechanical and Electrical Engineering, Kunming University of Science and Technology, Kunming , PR China a @qq.com, b kmgary@163.com, c wzdhbdjk@ 163.com, d kmyangao@163.com Keywords: Serial communication; LabVIEW; Frame header; High byte; Low byte; Odd-even check. Abstract. The techniques of serial communication utilized in a developed electrocardiogram (ECG) monitor programmed by the LabVIEW are introduced in the paper. By utilized the VISA serial communication functions included in the LabVIEW, some functions of serial ports such as opening and closing, commands sending and responses receiving, etc. can be easily called. Then, the communication between the ECG sensor and the ECG virtual instrument is established. By this way, the opening and the closing controls of the ECG sensor, the ECG data acquisition, the data processing and storage, the real-time drawing of the ECG waveform and so on can performed simply. As a result, serial communication by the LabVIEW make the program development of the ECG monitor becoming much quicker, more convenient and high efficient. Introduction LabVIEW is the NI graphical, interactive programming design environment, which provides a short way for the developing of virtual instruments with the characteristic of programming simple, intuitive results. It s widely utilized in data acquisition, control, analysis and presentation and so on. Users collect data through a variety of devices, including: GPIB, serial devices (RS 232/RS 485), PLC, and plug-in data acquisition cards. LabVIEW comes with powerful data analysis and signal processing package to meet the various calculations and analysis needs. In addition, in the design of the instrument display, LabVIEW virtual instrument design has its unique advantages. Therefore, we select LabVIEW as a software development platform. Serial communication is a commonly used method of data transmission between computer and computer, or between computer and peripheral equipments, which is widely used in data acquisition, monitoring and instruments control and so on. A serial port can be utilized to send or receive data by bits, which can be used in a line at the same time to send data at one thread, and with another to receive. Since it is simple for operation and it can be easily used to realize the remote communication, serial communication become more and more popular in various devices and instruments. There are four the most important parameters in serial communication viz. baud rate, data bits, stop bits and odd-even check. In the following sections, a serial communication development for a virtual ECG monitor is introduced, which is programmed by the LabVIEW. System design In order to guarantee the serial communication between the hardwares and the monitor, it means that the real-time data collected by the ECG sensors should be sent successfully through the serial port to the receiving port of corresponding software. What must be down is to realize the sensor open and close, the ECG data collection and processing, error processing, electrocardiogram preliminary drawing. The structure is shown in figure 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-21/02/16,07:43:06)

2 3004 Resources and Sustainable Development Fig.1 The Structure of System Hardware Connection. In the project, we used HKD - 10C, USB interface, single guide digital ECG signal module provided by Hefei Electronic Technology Research which can connect computer directly through the USB interface and output binary digital signal at the same time. Through the LabVIEW development platform, computer can connect the ECG sensors. The structure of the hardware connection is shown in figure 2, where the ECG sensor can be controlled by the code based on VISA serial communication function. Fig2. Structure of Hardware Connection Some Interface parameters are listed as follows: Physical connection: TTL serial port. Full duplex is used in the serial communication, in which the each command is composed by a start bit, eight data bits, 1 stop bit and a black & white even parity bit with the baud rate: BPS. The realization of the serial communication in the ECG monitor. For sending and receiving real-time ECG data accurately and rapidly, this serial communication using the way of PC sending an order and machines answer, which employed the VISA function and serial interface instrument communication provided by LabVIEW platform. VISA itself does not have programming ability, but provides a set of independent standard I/O bottom function for the user to call, which is convenient to realize the upper application and interface bus instrument communication. VISA instrument control simple process is shown in figure 3. Fig.3 Flow Chart of VISA Instrument Control High and low byte extraction of ECG data. The data format returned from the upper machine through ECG sensors (HKD 10C) is shown in figure 4. Fig.4 ECG data Format

3 Advanced Materials Research Vols A complete ECG data contains four parts: frame header, high byte, low byte, odd-even check. The frame header is utilized to identify the beginning in a data frame, which let PC know the data after frame header is useful. What we need is extract useful high byte and low byte of ECG data, and then integrate them into useful data to draw waveform (refer with Fig.5). Fig.5 Waveform drawing The received data are displayed in the form of string, which can't be used directly for data processing. What we need to do is convert a string to ASCII code. However, how to convert a string to ASCII code is still a problem? The method used in the developed ECG monitor is that using the string to byte array function in the LabVIEW to convert a string into the corresponding ASCII code. How to accurately find out the frame header, high byte, and the low byte? The method which we used is that locates the right frame header position and extract the ECG data. Firstly, the VISA read function is used to control the number of bytes read. For example, if the number of bytes need read is 5, the one dimension array search function is employed to find the frame head position. If it is located in zero, one, then the frame data valid data is located in 2, 3. Secondly, extract the high byte and the low byte of ECG data by using the index array function. Then a while cycle is added to realize the ECG data extraction continuously, which lays a foundation for subsequent ECG data analysis. ECG data processing. The extracted high byte and the low byte need to be processed before we use them to draw waveform. Firstly, switch the high byte and low byte string into ASCII code value, and then convert the ASCII value into double progress floating-point number. Then, integrate the operation. The specific operation method is use high byte multiplied by 256 and then plus the low byte. At last we get the needed ECG data to draw electrocardiogram. Error data Processing. In the test process, the entire program operation results will be affected if an error occurred at a certain moment. If there is an error occurred in the communication, all the data collected must be given up and recollect. What affects the data accuracy in ECG data acquisition process? Tests showed that it is the frame header which affects the data accuracy greatly. What make the program could not find the correct frame header? There are many factors such as external factors of interference, the user's improper operation, etc. And a most intuitive tip will be offered when a wrong data occurs, which help the users to recollect.

4 3006 Resources and Sustainable Development Conclusion The serial communication can realize serial ports opening and closing, commands sending and responses receiving, and achieve the communication between monitor hardware (ECG sensor) and software, and then indirectly realize the ECG sensor opening and closing, ECG data acquisition, processing and storage, drawing real-time ECG waveform and so on. With more convenient, strong expansibility and makes serial communication much quicker, the serial communication has been becoming a trend in during Engineering testing. Acknowledgements This work was financially supported by The Innovation and Entrepreneurship Plan of Yunnan province, 2012 (the project No ). References [1] Serial communication in the application of PCR instrument monitoring system Based on LabVIEW. Feng Zhou, Jingqi Yuan, Yuanmin Wu, the automation instrument of volume 26 eighth period in August 2005; [2] ECG measurement system based on LabVIEW Qin Xin Gao Fengmei Long Yunling the article code: (2008 ) ; [3] Serial communication of temperature controller Based on LabVIEW; Fei Xue; [4] ECG real-time monitoring measurement system Based on LabVIEW; HaoYu Wang, Zhongjun Hu, Xu Zhang, Zongying Gong, WentingLi Li, article Numbers: (2006) -; [5] ECG signal acquisition Based on LabVIEW. Xuxin Zhou, Yu Wang, Zulong Xu, Yuming Lei, article Numbers x (2008) the (a) 0039.

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