FarmInformationmeasurementandcontrolbyUsingWirelessRemoteMethods1.doc

精品論文推薦farm informatio n measur ement and c o n t ro l by usin g w i r e les s rem o te methods 1yong he* zhengjun qiucollege of biosystems engineeringcollege of biosystems engineeringand food science and food sciencezhejiang university zhejiang university hangzhou, p. r. china 310029 hangzhou, p. r. china 310029 abstractgsm is one of most important technology in wireless communication system, which contains three main services of short message, speech communication and data communication. aiming at the feature of farm information acquisition of large quantity information, real-time and working in field, the paper combined the gsm module with farm information acquisition, and advanced a new farm information measurement system using wireless communication technology namely gsm technology. the measurement system became more convenient after gsm technology putting to use. the system includes gps receiver, moisture sensor, a device which was designed by programming of single chip computer to measure soil moisture and positioning, two gsm wireless communication modules and a computer. the system could realize the function of transmitting the farm information to laboratory in the forms of gsm short message, and solved the problem of limitation of information storage and the inconvenience of carrying a datalogger device to the farmland.keywords: farm information; wireless remote; information measurement1 int r o ducti o nas the social economy is developing fast in 21st century, high speed, high performance, and convenience have become a very common demand of people. so as to existing wired communication technology cant yet meet the need of getting communication and information at anytime anywhere 1. however, the integration of internet and wireless communication technique make many applications change from ideal into reality, such as vehicle guiding, remote monitor, wireless internet, wireless pos, logistics control and etc. in a word, more and more devices are required to own the ability of wireless communication 2.there are several kinds of communication modes, and they can be classified into two parts of wired communication and wireless communication according to transmission medium. in the case of farm information acquisition, wired measurement mode is suited for fixed measuring points and persistent monitoring. the more the measuring points scatter, the higher the costs of information acquisition. a survey showed that costs for communication in large farmland and data scattered acquisition system were higher than the costs for monitoring 3. therefore, it is not properly to conduct mobile measurement and faraway field measurement by wired communication mode because of economic and technique problems.1 support by specialized research fund for the doctoral program of higher education(20040335034)-6-farmland information acquisition has its particularity for many reasons. first farmland information is mass and manifold and the measuring coverage is huge. second, field works have special needs on data acquisition device, such as power, volume and weight. finally, the system is required to have multi-channel measurement ability together with the possibility to obtain and handle multiplex signal at the same time. the traditional method to solve these problems is using wireless radio. however, there are still deficiencies in acquisition of farmland information, such as the costs of device is high, communication distance is short, using wireless frequency resource, easy to be interfered and etc 4. so a new farm information acquisition system by using wireless remote method and gsm technology was advanced in this article.2 wirele s s communicati o n te c h no logy and g s mgsm is short for global system for mobile communication system. it provides three main services of short message, speech communication and data communication. because service of short message make the wireless communication module more popular to be used, wireless communication module is also called gsm short message module 5. gsm short message service has the character of always online, no dialing, low price, large coverage and etc. for gsm technology, short message service is the only one that neednt set up end-to-end channel and also provide service when the mobile device is in point-to-point communication. short message service is asynchronous communication for sending only one sentence per each message. in gsm system, each message is handled as individual time and transmitted by smsc (short message service center).gsm can offer speed of 9.6 kbps data communication service when on-line whereas gprs can offer speed of 100kbps. considering the feature of farm information acquisition and the cost for communication, gsm short message service is suitable to use for transmitting data in large-scale field measurement system. there are two forms of short message service. one is point-to-point, message transmit from one user to another. the other is plot radio, where the message is sent to all registered users by smsc. due to point-to-point short message neednt set up specialized communication channel and the cost is cheap, it is adopted. each short message can transmit 160 coded data of 7 bits or 140 coded data of 8 bits or 70 unicode code. therefore, gsm short message could be used to transmit data and command in measurement and control systems which have low demands in real-time and transmitting speed, so virgin investment for building wireless communication network could be saved 6.gsm module is the kernel part to realize wireless data transmission. wireless communication module wmod2b based on standard of gsm produced by wavecom company is cited in this system. it belongs to commercial grade module with the characters of small volume (98*54*25mm), light weight (130g), low energy consumption (10ma at free state) and high performance. wmod2b module consists of mainframe, antenna, serial communication line, power line. it provides services of wireless modem, wireless fax, short message and speech communication 7. the short message service is suitable to apply in the situation of frequent transmittance of small data flow.the mainframe of wmod2b module is showed as below (see figure 1.):figure 1:the mainframe of wmod2b modulewmod2b module has three interfaces, as power, antenna and db15 communication interface. the module uses broad electric tension of 532 volt direct current and has direct current guard circuitinside the module. the module power is supplied by an electric accumulator. wmod2b module usesoutlay highly sensitive intensified antenna directly fixed beside the modem. the antenna shouldnt be shielded prevent from influence of signal receiving. db15 communication interface consists of a standard nine-pines rs-232 serial interface, speech interface and a reset line. it is only need to use rs-232 interface in this system and speech function is not cited.3c o nstruc tio n o f wireless ac quisition sy s t em in this paper the soil moisture quick-location testing device was used as an example for the wireless measuring system. the self-designed device connected with a moisture sensor and a gps receiver, so it could quickly and accurately obtain longitude and latitude and moisture content of the measuring points. as the device was designed by single chip computer, the memory capacitance is limited and it cant save a large quantity of data. therefore, traditionally the measuring device has to connect with a computer what is used to save data for further processing. however, this method is not proper to be used for two reasons. on one hand, the farmland is large and it always took long time to do the testing carrying with the computer from one point to anther. on the other hand, the computer is big and heavy and the power just lasts for about 2-3 hours. the new measuring system could solve this problem by sending farm information directly to computer by gsm wireless communication technology. the system includes a soil moisture quick-location testing device which was designed to measure soil moisture and positioning, two gsm wireless communication module and a computer. the construction of wireless data acquisition system is shown in figure 2.moisturesensorgps receivertestin grs-232gsm modulegsm modulecomputeoutdoor indoorfigure 2: gsm wireless data acquisition system3.1soil mois tu re qu ick - l oc ati on t es t i ng d evi ce soil moisture quick-location testing device is an important part to obtain information in this system. it picks gps location data and soil moisture content, and controls wmod2b module to send out data in the forms of short message. the at89c2051 type of single chip computer is cited as control center of the device. gps receiver could output several formats of location data according to standard of nmea-0183 8. single chip computer receives gps data and picks rmc sentences because it contains main location data, such as longitude and latitude and etc; the device uses swr-2 type of moisture sensor to measure soil moisture content. the analog signals outputted by moisture sensor are changed to digital signals by adc0809 analog-to-digital converter. then, volume content of soil moisture is gotten after some treatment of cpu.3.2 sms d ata se n d i ng modu l eone gsm module is used in this system as sms data sending module. it is in charge of sending farm information to smsc in forms of short message. wmod2b module is connecting with the testing device by rs-232 serial interface and controlled by at commands. at commands was first advanced by hayes company and became a standard modem command language system. before using gsm module to send out short message, it is necessary to set the module first, such as testing the signal strong or not and set short message pattern. there are three interface agreements to control sms in gsm system, block mode, text mode and pdu mode. in this system, text mode is used to send farm information and the max length of short message is 140 bytes. supposed use encode mode of 7 bits, it could send 160 characters.3.3sms d ata r e c ei vi ng m odu le another gsm module is used as sms data receiving module. its function is to receive short message, and transmit it to computer. wmod2b module has two modes to receive short message through smsc. one is received directly by serial interface. another is received by sim card. the mode of using serial interface is very easy but it need computer always on line otherwise the information will be lost. so the system chooses the mode of using sim card to receive short message. then the information which is received by wmod2b module would be transmitted to computer by rs-232 serial interface.3.4 d a ta a f te r-tr ea tmen t pr og r a mwhen using the wmod2b module to realize wireless communication, it needs software to communicate with computer and get data for further treatment. so a program for information fast-transmission was developed by visual basic 6.0 to realize the corresponding function of the system. the program was not only for receiving, sending, saving, deleting gps data and the value of moisture content, but also for advanced process of gps coordinate diversion, area calculation, graphic making and so on. the interface of the program is given below (see in figure 3.):figure 3:the interface of information fast-transmission programthe main functions of the program included:a. data receiving: the function of gathering gps information and moisture value could be realized by control unit of mscomm, and the information is showed on display windows. the value of ph and electric conduction could be also added as wished.b. data sending: the sending module was already designed by wavecom company and taken withwmod2b module, and it could be used to transmit experimental data or manual input data. c. data management: saving, searching and deleting received data.d. coordinate diversion: change gps longitude and latitude from original coordinates to plane coordinates.e. further treatment: calculate farmland area and make graphics of farm shape according to gps plane coordinates after diversion.4pract i cal appl ica tio n o f system the example was measuring soil moisture and position information of farm by wireless communication system. the experimental system was divided into two parts, an outdoor acquisition part and an indoor receiving part. (see in figure 4. and figure 5.)figure 4: devices for outdoor data acquisitionfigure 5: devices for indoor data receivingbefore the test, inserted two sim cards separately into the groove of two wmod2b modules. when testing, brought the acquisition part namely soil moisture quick-location testing device, map315 gps receiver and a wmod2b module to farmland. connected the communication lines, started the device, chose some sample points and plug the probe of the moisture sensor into soil. the gps orientation data and moisture value of the measuring point would be showed on screen of the device. at the same time, the data were transmitted to gsm module through rs-232 serial interface and sent to smsc in the forms of short message according to certain agreement.the receiving part was put in laboratory, included another wmod2b module and a computer. the computer should install the communication program and set number of smsc. when ready, the farm data were turn-sent by smsc to another wmod2b gsm module and showed on the windows of the program right away. lastly, saved all the gps data and moisture data of the sample points as a document.the test got the sample points by random sampling method, and the measuring time of each point is 20 seconds. there were totally 30 sample points. the measuring data had been handled by the extended function- spatial analysis of arcview3.3 and the results were showed in figure 6. the points in the map are the sample points. the depth of the color stands for how much the moisture content is, the deeper the color, the higher the moisture content. there are many lines in the map, which called equation lines, have same moisture content if the points are on the same line.figure 6:plane map of soil moisture content distribution.the result of the test showed that:(1) the moisture content is usually high due to the test was done after raining. the content are between 17.5%40.5% in these 30 sample points and the average value is 31.1%(2) it can be seen from the map that the distribution of soil moisture is not uniform. the moisture content of south part is higher than the north part.(3) the test indicates that data communication is successful, and farmland information wireless measurement system works well. though there is some data delay but this would not effect the data communication.5 co nc l us io n sthis paper introduced the common situation of gsm wireless communication technique, and applied in acquisition of farmland information. a new measuring system included gps receiver, moisture sensor, soil moisture quick-location testing device, two gsm wireless communication module and a computer was built. farmland geographic information and moisture value were measured by soil moisture quick-location measuring device and were transmitted real-time to a computer by using wireless remote method. the method solved the problem of limitation of information storage and the inconvenience of carrying large measurement device to farmland. the test proves that the measurement system is workable and has advantage of low cost, broad coverage and the data transmission distance is nearly unrestricted. therefore, it is a very effective way to measure farm information. in this paper the soil moisture quick-location testing device was used as an example of the wireless measuring system, but surely wmod2b module could be used in many farmland information acquisition systems as long as the testing device had rs232 serial interface for connection.r e fer en ce s1 qian ping(2003) wlan and agricultural informationization, computer and agriculture, pp. 20-22.2 zeng hui(2003) gsm wireless communication apply in changeable information mark system of highway,china tra