Networked Embedded Greenhouse Monitoring and ... - LaRIS - FESB

Networked Embedded Greenhouse Monitoringand ControlDarko Stipanièev, Member, IEEE, Maja Èiæ and Jadranka Marasoviæ, Member, IEEEAbstract— Networked embedded systems have become quiteimportant nowdays, especially for monitoring and control ofdistance and dislocated objects. Small greenhouses are typicalexamples. First, they are usually located far away from theowners house, and second, the plant grow is an example of theprocess which need constant 24 hours monitoring.In this paper networked embedded greenhouse monitoring andcontrol based on simple embeded web servers and 1-wireprotocol for conecting sensors and actuators is described.Hardware and software architecture of embedded web servers isanalysed and the experimental results of monitoring and controlof laboratory greenhouse is presented.Index Terms — Embedded web server, Greenhouse Monitoringand Control, Internet, Networked Embedded Systems, TINI, 1-Wire protocolTI. INTRODUCTIONoday, advances in sensors, actuators andmicroprocessor technology, both on hardware andsoftware level, have enabled distributed implementation ofsensor and control actions over sensor/actuators networks.If we connect such local sensor/actuators, private networksto global network (Internet) additional features could beexhibit. The monitored and controled system could becomeaccessible from almoust anywhere. The process parametersdata display, remote control, system testing and systemreconfiguration could be done using standard browsers onworkstation computers. That alows us to use large screens,menus, buttons, on-line helps, instead of simple alpha –numeric displays usually connected to such embeddeddevices.The bridge between distributed sensors and actuators onThis work was supported in by the Ministry of Science andTechnology of Republic Croatia under Grant TP-01/0023-02"Embeded Web servers in Monitoring and Control of dislocatedsystems" and in part under Grant 0023008 "Intelligent Agents inModeling and Control of Complex Systems".Authors are with Laboratory for Modelling and Inteligent Systems(http://laris.fesb.hr), Faculty of Electrical Engineering, MachineEngineering and Naval Architecture, UNIVERSITY OF SPLIT,R.Boškoviæa bb, 21000 Split, C r o a t i a. D.Stipanièev (e-mail:dstip@fesb.hr ), M.Èiæ (e-mail: maja.cic@fesb.hr), J.Marasoviæ(e-mail: jadranka.marasovic@fesb.hr ).one side and Internet on the other side could be embeddedWeb servers. They are low cost devices which allow us touse standars network protocols like TCP/IP and HTTP.In this paper greenhouse monitoring and control systembased on simple 1-wire sensor/actuators local privatenetwork and embedded Web servers for connecting thisnetwork to Internet is described.Sysem design, protocols, software and hardwarerequirements for embedded Web servers are presented,detail description of greenhouse monitoring and controlsysstem is given together with experimental results oflaboratory greenhouse model monitoring and temperaturecontrol.II. EMBEDDED WEB SERVERS SYSTEM DESIGNEmbedded systems require web server software thatenhance their networking functionality without taking upvital system resources. Web enabling of devices is possibleby adding web server software to existing embeddedsystem. Requirements for embedded Web servers are:- Small memory footprint: Server must use very littlememory and it must not fragment memory. Manyembedded devices use simple memory allocators thatcannot manage memory effectively. This problem isusually solved by using statically allocated or preallocatedmemory blocks.- Dynamic page generation: Since the content of the pagesserved will be status information and sensor readingspart or all of the web pages will have to be generated onthe fly.- ROMable web pages: Since embedded systems do nothave disk drives or any other memory storage units, webpages and other web content have to be stored in ROMor flash.Reducing embedded web server capabilities to minimalset of necessary functions makes hardware requirements aswell as energy consumption very small. Thereforedimensions and the price of the device are miniaturecompared to the desktop PC with full functionalitypreserved at the same time.

A. ProtocolsAlthough TCP/IP (Transmission ControlProtocol/Internet Protocol) is the main communicationprotocol that enables connection of different devices innetworks, it is not implemented in full. Only the necessaryparts are used and parts that are not needed for this sort ofcommunication are excluded. Furthermore, TCP/IPprotocol is basis for upper level network protocols whichwill be used in embedded systems. If the system uses RS-232C or modem link then point-to-point (PPP) or serial-lineInternet protocol (SLIP) is needed. File transfer protocol(FTP) is used for uploading new files and programs to thesystem. Opposite to the receiver-driven information flowthrough Web browser, information flow could be devicedriven.Using Simple Mail Transfer Protocol (SMTP)application can periodically send information via e-mail.B. SoftwareA minimal set of software for embedded Internet systemincludes an operating system and application software, ahttp server, a TCP/IP stack, and drivers for communicationhardware. The use of Internet allows the embedded systemto offer substantial online capabilities without using systemresources. With HTML pages pointing to other networklocations, the system can offer more online documentationand richer graphics than the system hardware couldotherwise support. In addition, supplying the raw data tomore powerful “partner” on the network and presenting theresults of “partner” calculations can virtually increase thesystems processing power. As we can see with cleverprogramming and the use of Internet, systems capabilitiescan be virtually increased to a higher level. The presence ofembedded web server must not obstruct the systemsprimary real-time operation in any way and thereforesystem response must be compromised to main function.The Internet software should not be the limiting factor forthe speed of data flow between the server and the browser.The HTML pages should not be burdened with extensivegraphics. The presence of too many graphical elementsconsumes much more memory than text and therefore takesmuch more time to download to browser. The pagedownload time should be acceptable for the user, not longerthan couple of seconds. [1].C. HardwareHardware requirements result from the given selection ofrequirements and a set of software to resolve thoserequirements. The minimal setup for network enabling ofembedded systems includes 8-bit microprocessor, Ethernetand/or serial interface and enough memory to store and runapplications. No I/O devices are needed since all thisoperations are managed through Internet.Further system improvements depend on desired systemprice and capabilities. These 8-bit devices can address up to16MB memory and often include hardware-acceleratedinterpreters for higher-level languages, which make themadequate for this purpose. Memory storage devices such ashard disk drives are definitely optional and most of thesedevices will run software directly out of ROM or flashinstead of loading it into RAM memory. This enables thesystem to boot in just a second or two as opposed to theminutes that a desktop Windows system can take.D. System DesignIn a new system design, system hardware will be chosenaccording to the overall requirements of the system.Application software needs to be developed in order toachieve the required system functionality. System designermust compromise between hardware and software solutionsfor each problem. Hardware solutions are easier to design,faster and more accurate in operation. Software solutionresults in smaller production cost and system modificationsare simpler. Particularly, connection to Internet must beconsidered. When embedded processor is located in thevicinity of local network installation, 10Mbps Ethernetinterface is chosen. Otherwise, serial port is used to transferdata over telephone or radio channel.For the program development any software developmentkit can be used, with the additional libraries supplied by thehardware manufacturer. Since the software will bedeveloped on a different platform, portability is veryimportant for the embedded systems. Java, as objectoriented, platform independent programming language,eliminates the need to recompile applications when movingto a different processor. Since a complete set of standardclass libraries is available, there is less code to write andmaintain. HTTP and FTP client support is built in alongwith support for handling URLs, IP addresses and nameresolution.To put a web server on a device, the server must be ableto generate dynamic web content based on data from thedevice. Although it is not necessary to support a largenumber of users, the Web server must process multiple,simultaneous browser requests.III. NETWORK EMBEDDED GREENHOUSE MONITORING ANDCONTROLNetwork embedded greenhouse monitoring and controlsystem is a small-size network of tightly coupledphysical/information system components (sensors,actuators, processing and communication resources) withlimited reliability and changing physical topology. Thesystem core is Embedded Web Control Unit connected onone side to sensor/actuator local network and on the otherside to Internet.Between existing interface devices, minimalconfiguration suitable as a working interface needed forlow-cost networking is TINI TM [2], so we have choose himas a central part of our Embedded Web Control Unit.

The TINI board is a Java TM computer that uses a TINIchip set plus 512 Kbytes commodity SRAM and interfacecircuitry in a 68-pin SIMM stick form factor. TINI’s threechipchip set consists of a DS80C390 processor, 512Kbytes Flash ROM containing the firmware and anEthernet controller.Optimised for the embedded Java environment, theprocessor supports 24-bit addressing, an 8/32-bitCPU/ALU, and high clock rates (~60 MHz and beyond),and other Java enhancements. One of the most interestingTINI features is its I/O ports. TINI has Ethernet 10Base-Tinterface, 1-Wire® net interface and dual serial (RS-232)ports. Ethernet interface is used for permanent Internetconnection, serial port for dial-up modem Internetconnection and 1-Wire net interface for sensors andactuators connection.TINI software is divided into categories: run-time codein Flash ROM (the RTOS, TCP/IP stack, Java VM andAPI packages) and high-level networking protocols (FTP,TELNET, DHCP, DNS), development tools (JDK) andJava applications.TINI OS is very small and provides basic services suchas task scheduling, a file system, and memory and I/Omanagers. Unlike most small, embedded controlleroperating systems, TINI OS is designed to switchheavyweight tasks. Specifically, it is optimised to switchbetween multiple executing instances of a Java byte codeinterpreter. This provides the foundation required forrunning multiple Java applications. Multiple native/kernelprocesses are managed through cooperative multitaskingand are therefore subject to tight execution timerequirements.All sensors and actuators are connected to DallasSemiconductor 1-Wire Net [3]. 1-Wire Net uses one signalfor both, power and network connection. Each sensor oractuator has its own 1-Wire chip with a unique ROMregistration number that contains a family code, serialnumber and a CRC for checking the correct delivery of theregistration number.The sensors used inside our experimental greenhousemodel were temperature and humidity sensors, but parallelywe have monitored the weather conditions outside thegreenhouse (temperature, wind speed and wind direction)having im mind future predictice control algorithms. Insidetemperature were measured in the air, on the groundsurface and 5 cm inside the ground. Other type of sensors,like barometric preasure or lighting sensors can beconnected too.The temperature and humidity inside the greenhousecould be controlled using heaters, overheat protectiondevices (ventilators) and water wetting system.Laboratory, experimental greenhouse is shematicallyshown on Fig.1. and Fig.2. shows the laboratorygreenhouse model.Fig. 1. T0, T11, T12, T13, T21, T22, T23 are temperature sensors and H0is the humidity sensor. Actuators are heater, wetting system and vent1 andvent2 for overheat protection.Fig. 2. Laboratory greenhouse model used in our experimentsEmbeded Web Control Unit is shown in Fig.3.1-wire sensors could be parallely connected, so almoustunlimited number of sensors could be used. Of course,practically, there are some limitations because the processorhas limited capacity. We have succesfuly worked with 30sensors, and that is more than enough for any greenhouseapplication.Embedded Web Controller software is conceived as acollection of servlets – software agents, runing parallely,each of them performing one specific task. The central oneis MonitoringServlet responsible for reading 1-Wiresensors and displaying data in the form of dynamic HTML

Fig. 3. Embedded Web Controller based on TINI embedded Web serverpage. Fig.4. shows typical monitoring screen layout.file. The third servlete is ArchiveServlet which isresponsible for process data archive. All proces variablesvalues are stored in predefined intervals to process.xml file:3A0008000F51401021.012:39:131< sample >720008000F469810< value >21.5< time >12:39:17< no >1…As the Embedded Web Server memory is not big enough tostore archive files, they are stored to another standard Webserver. JavaScript/JavaApplet program was writen todisplay the archive data. Fig.5. shows one example ofdisplaying archive temperature data.Fig. 4. Monitoring HTML page created by MonitoringServletThe important feature of the designed system is thepossibility of 1-Wire topology changing without anyinfluence to system funcionality. The special software agentDefineServlet check the 1-Wire network, detect the actualsensor/actuator network configuration and writeidentification numbers in xml file address.xml Detailsensor description (min, max values, units) could beinserted in the same file using special Web form.Temp. T03A0008000F514010-1045°C. . .Fig. 5. Displaying archive temperature data using JavaScript/JavaAppletapplicationFor control purpose, four control servlets weredeveloped, each of them responsible for its type of control.Fig.5 shows the control dynamic HTML page created bycentral ControlServlet . The ControlServlet is activatedfrom the main monitoring page and it is protected byUserID and Password.Before displaying process parameter valuesDefineServlet read the sensor identifacion date from xml

Fig. 5. Control HTML page created by ControlServletFour types of control procedures were applied:a) Simple switch on – switch off control of all actuatorsusing output relays. Any actuator could be remotely switchon and switch clicking in the appropriate checkbox inControl Web page (OnOffServlet).b) Feedback on – off control. The user chose thecontrolled variable (for example temoerature T0 fromFig.2) and its referent value (FeedbeckOnOfServlet).c) Feedback discrete PID and DDC control based ondifference equation:u n =k 0 *u n-1 +k 1 *e n +k 2 *e n-1 +k 3 *e n-2where u n and u n-1 are controle signals in nT and (n-1)*Ttime instant, e n , e n-1 and e n-2 are error signals in nT, (n-1)*T and (n-2)*T time instant and k 0 , k 1 , k 2 and k 3 areregulator constants defined by user through standard Webform (DDCServlet).d) The time on – off control. This type of control isespecially important for wetting system but it could be usedfor any actuator. The user choose the time moments whenone of actuators would be swiched on and time duration ofits activ state, For example the wetting system could beswitched on at 6:00 , 12:00 and 18:00 for 20 seconds(TimeOnOffServlet).Fig.6. shows two control examples. The first one, shownin Fig.6a) is temperature control using heater and thesecond one, shown in Fig.6b) is temperature control usingcooling devices (ventilators).Fig. 6. Temperature control using a) heater and b) ventilatorsIV. CONCLUSIONIn this paper we have presented network embeddedgreenhouse monitoring and control based on embeddedWeb server unit which gather and route data from localsensor/actuator network to global network - Internet.The developed experimental system, based on TINIembedded Web server, collect data from distributed sensorsand activate connected actuators using simple 1-wire localnetwork. On the other side Web server is connected toInternet through Ethernet or dial-up network. Thedeveloped system shows all advantages of NetworkEmbeddes System Tecnology (NEST), like the possibilityof changing physical topology and low dimensions and costin comparison with PC based system, preserving the fullfuncionality at the same time.REFERENCES[1] R.A.Quinnell: “Web servers in embedded systems enhance userinteraction”, EDN Magazine, April 10. 1997.[2] Tiny InetrNet Interface, www.ibutton.com/TINI[3] D. Awtrey: “Transmitting Data and Power Over a One-Wire Bus”,Sensors, February 1997, pp. 48-51[4] J. Turley: "Microprocessors for Consumer Electronics, PDA's andCommunications", Embedded Systems Conference, September 26.-30. 1999.[5] M. O’Brien: “Embedded Web Servers“, Embedded SystemsProgramming, November 1999.www.embedded.com/internet/9911/9911ia2.htm