Body AreA SenSor NetworkS: ChAllengeS And OpportunItIeS
C OV E R F E AT U REBody Area Sensor Networks:Challenges and OpportunitiesMark A. Hanson, Harry C. Powell Jr., Adam T. Barth, Kyle Ringgenberg,Benton H. Calhoun, James H. Aylor, and John Lach, University of VirginiaBody area sensors can enable novelapplications in and beyond healthcare,but research must address obstacles suchas size, cost, compatibility, and perceivedvalue before networks that use suchsensors can become widespread.Inroads into coordinated, intelligent computingare enabling sensor networks that monitor environments, systems, and complex interactions ina range of applications. Body area sensor networks (BASNs), for example, promise novel usesin healthcare, fitness, and entertainment. Each BASNconsists of multiple interconnected nodes on, near, orwithin a human body, which together provide sensing,processing, and communication capabilities.BASNs have tremendous potential to transform howpeople interact with and benefit from information technology, but their practical adoption must overcomeformidable technical and social challenges, as the “Re-58computerquirements for Widespread Adoption” sidebar describes.These challenges have far-reaching implications but offermany immediate opportunities for system design andimplementation.Although BASNs share many of these challengesand opportunities with general wireless sensor networks (WSNs)—and can therefore build off the body ofknowledge associated with them—many BASN-specificresearch and design questions have emerged that requirenew lines of inquiry. For example, to achieve social acceptance, BASN nodes must be extremely noninvasive, anda BASN must have fewer and smaller nodes relative to aconventional WSN. Smaller nodes imply smaller batteries,creating strict tradeoffs between the energy consumed byprocessing, storage, and communication resources and thefidelity, throughput, and latency required by applications.Packaging and placement are also essential design considerations, since BASN nodes can be neither prominent noruncomfortable.As with any technology, economic concerns can affectBASN adoption. To amortize nonrecurring engineeringcosts, each BASN platform will require either significantvolume in a single application or aggregate volume acrossPublished by the IEEE Computer Society0018-9162/09/ 25.00 2009 IEEE
several applications, creating design tradeoffs betweenapplication-specific optimizations and general-purposeprogrammability.Finally, value to the user will ultimately determine thetechnology’s success. BASNs must effectively transmitand transform sensed phenomena into valuable information and do so while meeting other system requirements,such as energy efficiency. A BASN’s value therefore restsin large part on its ability to selectively process and deliver information at fidelity levels and rates appropriate tothe data’s destination, whether that is to a runner curiousabout her heart rate or a physician needing a patient’s electrocardiogram. These disparate application requirementscall for the ability to aggregate hierarchical informationand integrate BASN systems into the existing informationtechnology infrastructure.Current work to address these challenges and realizethese opportunities points to a critical need for collaboration between technologists and domain experts who canhelp define the specifications and requirements for BASNsystems and applications. In applications targeting theaging population, for example, such collaboration couldinvolve physicians, nurses, psychologists, and sociologiststo ensure that a BASN provides valuable information whilebeing usable by the elderly in a safe and socially acceptable manner. The need for such collaboration is only oneof many requirements that research must satisfy to pavethe way for practical, accessible BASN use.application areasBecause of demonstrated need and market demand,BASN research thus far has concentrated on healthcareapplications, addressing the weaknesses of traditionalpatient data collection, such as imprecision (qualitative observation) and undersampling (infrequent assessment).In contrast, BASNs can continuously capture quantitative data from a variety of sensors for longer periods. Byaddressing challenges such as the energy-fidelity tradeoff, BASNs will enable telehealth applications—medicinebeyond the confines of hospitals and clinics1—and, becauseof their human-centricity, will facilitate highly personalized and individual care. As Figure 1 illustrates, BASNsintegrated with higher-level infrastructure will likely excelin healthcare scenarios, serving the interests of multiplestakeholders.In addition to delay-insensitive applications such aslongitudinal assessment, BASNs that can offer real-timesensing, processing, and control will augment and preserve body functions and human life. BASN researchersare already working to improve deep brain stimulation,heart regulation, drug delivery, and prosthetic actuation.BASN technology will also help protect those exposed topotentially life-threatening environments, such as soldiers,first responders, and deep-sea and space explorers.Finally, BASNs are well positioned to benefit fromthe intersection of two formerly disparate applicationareas. Physiological and biokinetic sensing applicationsRequirements for Widespread AdoptionWidespread BASN adoption and diffusion will depend on a hostof factors that involve both consumers and manufacturers.User-oriented requirements include the following: Value. Perceived value can depend on many factors, such asassessment ability, but overall, the BASN must improve itsuser’s quality of life. Safety. Wearable and implanted sensors will need to be biocompatible and unobtrusive to prevent harm to the user.Safety-critical applications must have fault-tolerantoperation. Security. Unauthorized access or manipulation of systemfunction could have severe consequences. Security measures such as user authentication will prevent suchconsequences. Privacy. BASNs will be entrusted with potentially sensitiveinformation about people. Protecting user privacy willrequire both technical and nontechnical solutions. BASNpackaging will need to be inconspicuous to avoid drawingattention to medical conditions. Encryption will be necessary to protect sensitive data, and encryption mechanismswill need to be resource-aware. Compatibility. BASN nodes need to interoperate with otherBASN nodes, existing inter-BASN networks, and even withelectronic health record systems. This will require standardization of communication protocols and data storageformats. Ease of use. Wearable BASN nodes will need to be small,unobtrusive, ergonomic, easy to put on, few in number,and even stylish. On-body and off-body user interfaceswill need intuitive controls and presentation ofinformation.Beyond user concerns, BASN manufacturers will face imposing and expensive regulatory processes (FCC certification andFDA approval, for example) to get products to market. Oncedeveloped, BASN systems will likely involve a complex web ofstakeholders (users, emergency services, caregivers, physicians,researchers, and so on). Each stakeholder will provide value toand derive value from BASN systems. Such dynamics createcomplex relationships that raise ownership and liability issues.Who will pay for BASN systems? Who will own BASN data? Howwill access to data and information be granted? Who is liable fordamages involving BASN systems? These questions must beanswered to protect all stakeholder interests and to promoteBASN systems’ widespread adoption and diffusion.JANUARY 200959
cover F E AT U REare increasing as athletes and fitnessenthusiasts seek to improve human performance, while gaming systems arepushing their envelope by integratingmore sophisticated interfaces based onhuman movement. With the crossing ofthese markets, BASNs are well positionedto deliver the biofeedback and interactivity necessary for next-generation fitnessand entertainment applications.Body Area SensingFigure 1. A body area sensor network and its environment. A BASN caninteract with existing systems, such as networks in hospitals and retirementcommunities. Body sensors in BASN nodes provide data to the bodyaggregator, which is central to managing body events. Body aggregatorsperform a multitude of functions, including sensing, fusing data from sensorsacross the body, serving as a user interface, and bridging BASNs to higher-levelinfrastructures and thus to other stakeholders.Figure 2. BASN node architecture. Although the architectural componentsare similar to those of a typical wireless sensor network node, a BASNnode presents unique challenges and opportunities—from sensing tocommunication. The sensor node (left) is the TEMPO inertial sensor nodedeveloped at the University of Virginia.60computerAs Figure 2 shows, BASN nodes createan interface to humans, typically encapsulating an energy source, one or moresensors, a mixed-signal processor, and acommunication transceiver. Some nodesalso support data storage or feedbackcontrol to body-based actuators, such asan insulin pump or robotic prosthetic.Although BASN and WSN nodes have similar functional architecture, differences intheir operational characteristics—sensing, signal processing, communication,caching, feedback control, and energyharvesting—present unique challengesand opportunities for BASN nodes.SensorsSensing is fundamental to all sensornetworks, and its quality depends heavilyon industry advances in signal conditioning, microelectromechanical systems(MEMS), and nanotechnology. Sensors fallinto three categories. Physiological sensors measure ambulatory blood pressure,continuous glucose monitoring, core bodytemperature, blood oxygen, and signalsrelated to respiratory inductive plethysmography, electrocardiography (ECG),electroencephalography (EEG), and electromyography (EMG). Biokinetic sensorsmeasure acceleration and angular rate ofrotation derived from human movement.Ambient sensors measure environmental phenomena, such as humidity, light,sound pressure level, and temperature.Although the number of sensors in theBASN in Figure 1 might seem unrealistic, BASN users are likely to tolerate andaccept some degree of burden if they perceive enough value in doing so.Sensors in typical WSNs are numerous, homogeneous, and generally
Signal processingSignal processing is needed to extract valuable information from captured data that stems from transient events,such as falls, as well as from trends, such as the onset offever. BASNs may need to concurrently capture, process,and forward information to different stakeholders. Timecritical information from both events and trends wouldgo immediately to emergency services, for example, butinformation that is not sensitive to delays would go to thephysician for review later on.Figure 4 shows the power consumption of wirelesstransceivers and microprocessors in popular BASN andWSN platforms. It underlines two characteristics of existing embedded technology: Processing data at a given rateconsumes less power on average than transmitting the datawirelessly, and reducing the data rate will reduce powerconsumption for both wireless transceivers and microprocessors. These characteristics create a tradeoff betweenprocessing and communication: On-node signal processingwill consume power to extract information, but it will alsoreduce in-network data rate and power consumption.Arbitrary data-rate reduction will lower the transmitted information’s fidelity, and for lossy compressionschemes, a rate-distortion analysis would need to definethe limits of such a reduction. Low-power computationaltechniques such as dynamic voltage-frequency scalingor dynamic power management will create opportunities for dynamic adjustment of algorithmic complexity,and therefore trade off energy and fidelity based on anapplication’s predefined or situational needs. Contextawareness and predictive models might better inform andguide processes that control data reduction.Resource constraints challenge BASNs, including integer-only math, limited memory ( 20 Kbytes), and limited10,000Power consumption (mW)1, 0001 001010.110–210–1100101102Date rate (bps)103104105Figure 3. Average power consumption of continuousambulatory monitoring applications. These differencessuggest the need to support multiple applications in anarrow range of data rates (such as combining ECG, EEG,and EMG on a single node) or to support a single applicationacross a wide range of data rates, such as acceleration.ABP: ambulatory blood pressure; CGM: continuous glucosemonitoring; L, T, SPL: light, temperature, sound pressurelevel; SpO2: pulse oximetry; RIP: respiratory inductiveplethysmography; ECG: electrocardiography; EMG:electromyography; EEG: electroencephalography.10,0001, 000Power consumption (mW)insensitive to placement error. BASN sensors, in contrast,are few, heterogeneous, and require specific placement.Indeed, ineffective placement or unintended displacementfrom movement can significantly degrade the captureddata’s quality. Such requirements call for strategies thatwill minimize and detect placement error, such as betterpackaging combined with on-node signal classification.Commercial sensors exhibit a wide range of powersupply requirements, calibration parameters, outputinterfaces, and data rates. Figure 3 shows the power consumption and data rate across a sampling of commercialsystems for continuous, ambulatory monitoring. Engineering BASN nodes to accommodate this breadth of sensingrequirements could necessitate an application-specificapproach that minimizes the design space, improves efficiency, and amortizes cost over a single application.Likewise, BASN nodes designed with a high degree of configurability could amortize cost over a much larger rangeof applications, including those unforeseen.1 001010.1103104105106Date rate (bps)107108Figure 4. Average power consumption of wirelesstransceivers (orange) and microprocessors (blue) intypical BASN and WSN platforms. For a given data rate,wireless transceivers consume more power on averagethan processors. Reducing an application’s data rate byextracting only the essential information will reduce powerconsumption.clock frequency ( 20 MHz). Therefore, BASN nodes mustbreak complex signal-processing tasks into manageablesegments to minimize algorithmic complexity whilemeeting real-time deadlines. Such efforts will necessitateoperating systems that allow access to efficient hardwareperipherals. In addition, work is needed to create featureextraction algorithms and classification methods that areeffective yet are not so computationally complex that theywould be infeasible for resource-constrained hardware.JANUARY 200961
cover F E AT U RECommunicationCommunication is essential to node coordination.BASNs are unique in that they attempt to restrict thecommunication radius to the body’s periphery. Limitingtransmission range reduces a node’s power consumption,decreases interference among adjacent BASNs, and helpsmaintain privacy. WSNs typically communicate over radiative radiofrequency (RF) channels between 850 MHz and2.4 GHz. Unlike WSNs, wireless BASNs are challenged bythe dramatic attenuation of transmitted signals resultingfrom body shadowing—the body’s line-of-sight absorption of RF energy, which, coupled with movement, causessignificant and highly variable path loss.The deployment and control ofprosthetics or remote roboticassistive devices is a possibleapplication of BASNs.Preserving quality of service (QoS) over traditionalwireless links could require one of several approaches,including adaptive channel coding; transmission powerscaling; multiple input, multiple output; novel transceiverarchitecture; and QoS-aware media access protocols. Ultrawideband communication could help mitigate aspectsof this problem in the near future.2Technologies such as smart textiles, magnetic induction,3 and body-coupled communication4 also showlong-term promise. In smart textiles, wires are embeddedin clothing, thereby reducing communication power overhead and simplifying networking schemes.5 Cost, ease ofcleaning, and manufacturer standardization could limitmarket uptake.Magnetic induction uses magnetic near-field effects tocommunicate between two coils of wire. Near-field communication typically suffers less path loss than radiativecommunication, but coil dimensions complicate packaging.Despite this complication, implantable and swallowed sensors have exploited this communication technology.Body-coupled communication uses the human body as achannel. BASN transceivers of this nature are either in contact with, or capacitively coupled to, the skin. Body-coupledcommunication is appealing because little radiated energyis detectable beyond the human body, channels are highlystable, and energy requirements are low. However, additional research will need to determine the safety of thisapproach.Future BASNs might implement several types of transceivers to serve situational needs. For example, a sensornode could employ both lower data rate, lower power communication transceivers in parallel with higher data rate,62computerand higher power transceivers for both longitudinal andcritical communication needs. Transceiver diversity couldalso help mitigate body shadowing.StorageThe microelectronics industry is exploring lower powernonvolatile memory such as MRAM and RRAM. Consequently, the availability of on-node storage might enhanceBASN functionality. Because long-term data collectionoften needs no real-time aggregation, on-node storage isa reasonable solution for archiving data, thereby increasing battery life.Longitudinal assessment is insensitive to delay metricsthat challenge time-critical monitoring. Some applicationsmight choose to cache data until body channel conditionsare more favorable for transmission. Consequently, conditional caching could prolong battery life, decrease formfactor, or decrease bit errors.On-node storage could also be used to archive data forsignal classification. By storing biokinetic gait patterns overtime, for example, a BASN could learn to classify healthygait from pathological gait. Such an archive could informthe signal-processing routines needed to detect longitudinal trends (recovery from surgery) and instantaneousevents (falls).Feedback controlBASNs open exciting opportunities for augmenting andassisting bodily functions. Medical devices such as deepbrain stimulators now run in an open-loop mode becauseno local feedback is available from the brain’s centralcortex to adjust the stimulator’s excitation cycles. The accurate and reliable assessment of tremor through bodyarea sensors could change that by empowering feedbacktremor control.The deployment and control of prosthetics or remoterobotic assistive devices is another possible application.EMG signals from the eyelid or jaw might be used to control a device that assists or replaces a limb or to activate arobotic device that opens doors or controls simple household appliances. Other forms of feedback control includedrug delivery and blood glucose regulation facilitated byimplantable biochemical sensors.Clearly, if BASNs are to control or help assess life-criticalphysiological events, they must be reliable. Unlike traditional WSNs, the failure of one BASN sensor could threatenlife. Such applications will require fail-safe, fault-tolerantdesign principles.Energy harvestingAlthough the microelectronics industry has faithfullyadhered to Moore’s frenetic pace, advancements in commercial battery technology have been gradual. To remaina practical energy source for BASNs, battery technology
Body Area NetworkingNetworking among devices in, on, and around the bodyposes unique challenges for resource allocation, sensor3.02.5Harvestable power (mW)must continue to increase energy density, and investmentsin increased energy density must have commensuratelevels of investment in battery safety—particularly in lightof recent battery recalls.The high energy density of lithium-based batteries ishelping power many portable consumer technologies. Suchbatteries work well for handheld electronics, but their capacity is limited in diminutive BASN enclosures. The needto replace or recharge batteries frequently makes BASN useless desirable. Supercapacitors and carbon-nanotube-basedenergy stores have great potential to improve battery capacity, but have not yet matured to commercial availability.Energy harvesting—taking energy from ambientsources, such as sunlight or vibration—is an attractive solution to energy woes. Recharging batteries with harvestedenergy could not only extend battery life, but also simplifyBASN use. Research challenges are formidable becauseof node placement variability and uncertainty about theuser’s exposure to ambient energy. These realities severelyconstrain opportunities.Figure 5 shows the results of our investigation to estimate the average power that a BASN user can harvestper hour per day. For each of seven energy-harvestingsources,6 we correlated the amount of power available persquare centimeter with that source’s availability duringcommon human activities. We then compiled statisticsfrom the US Department of Labor’s 2007 “American TimeUse Survey” (www.bls.gov/tus) on the percentage of Americans engaged in each activity at a given hour.The figure shows an optimistic view of harvestablepower, thus defining an upper bound for a system’s powerconsumption from harvesting alone. The total powershown is available only if someone deploys all sources(at 1 cm2 each) simultaneously and combines their poweroutput. The data also illustrates a pronounced blackoutperiod that renders these BASN nodes nearly powerless.Finally, the available harvestable power will differ substantially among individuals, which means it will be necessaryto carefully match application profiles to activity levels inthe target demographic.Energy-harvesting sources vary widely in the energyavailable per area. For example, a solar panel in full outdoor sunlight provides up to 15 mW per square centimeter,but the same device generates only 10 µW in indoor lighting for the same area. Both placement and packagingwould be affected by such variation.Thus, although increasing battery life through harvesting would revolutionize BASNs, more research is neededto create highly efficient hybrid solutions that incorporateenergy generation and storage.2.0VibrationsPressure variationAir flowHuman powerTemperatureSolar (inside)Solar (outside)1.51.00.5002468 10 12 14 16 18Hour of the day (military time)20 22Figure 5. Results of correlating seven energy-harvestingsources with each source’s availability over an average workday. Each segment represents the average amount of powerthat an individual could expect to harvest at any given timewhen all sources are being deployed. Nightly blackouts are aparticular challenge and will require efficient energy storagemechanisms.fusion, hierarchical cooperation, QoS, coexistence, andprivacy. On the one hand, minimalistic networking techniques increase system runtime and reduce obtrusiveness;on the other, sacrificing QoS or privacy is unacceptablefor life-critical or sensitive medical applications. BASNsintroduce a wide range of application scenarios, yet it isnot certain if a unified network solution is preferable overapplication-specific protocols and topologies.Unlike conventional WSNs, BASNs are generally smaller(fewer nodes and less area covered) and have fewer opportunities for redundancy. Scalability can lead to inefficiencieswhen working with the two to 10 nodes typical of a BASN.Adding sensor and path redundancy to address node failure and network congestion might not be a viable strategyfor a BASN seeking to minimize form factor and resourceusage. Consequently, the focus must be on generating intelligent and cooperative QoS for the nodes.On-body and in-body (implantable) networks exhibitheterogeneity because of placement constraints and sensorrequirements. Wearability requirements can vary drastically across applications. Some call for multiple wirednetworks in a single garment; others call for multiplewirelessly networked devices securely attached at various body locations; and still others call for ultraminiature,biocompatible implanted devices with less frequent communication to the outside world.BASNs also have a distinctly hierarchical nature. Theycapture large quantities of data continuously and naturalistically, which microprocessors must process to extractactionable information. Data processing must be hierarchical to exploit the asymmetry of resources, preserve systemefficiency, and ensure that data is available when needed.JANUARY 200963
cover F E AT U REof wireless technologies, such asBluetooth, cellular, and IEEE 802.11;interactive user interfaces such astouch screens; and highly capableembedded microprocessors, such asthe ARM 11 and OMAP, make newermobile phones and personal digitalassistants attractive hosts for bodyarea aggregation.At the body aggregator, data processing must reveal relationshipsamong a body’s sensors. With proFigure 6. Hierarchy of networks and resources. Data processing starts with thegressively richer resources, moreindividual BASN and progresses through communication with existing wirelesssophisticated and dedicated datatechnologies via the Internet. Because power consumption and data rate increasemining systems could uncoverwith each processing level, hardware and software will need to interoperateinformation related to small andthrough multiple levels of infrastructure to share information.large populations. Each successivehierarchical level must aggregateFigure 6 shows the levels and their respective requiremore data by supporting higher data rates, making morements for data processing, archiving, and management.general inferences, and archiving more information.During data fusion, systems can detect or react to notableConsequently, hardware and software will need to interoccurrences from dynamic data, explicit queries, and sooperate through multiple levels of infrastructure to shareon. Specific reactions might include heightening the stateinformation. Moreover, information gained at each levelof awareness, collecting data at a higher fidelity for closerwill provide feedback to and inform the refinement ofinspection, forwarding events to higher levels, or evenclassification schemes, feature-detection algorithms, andimmediate response.sensor coordination, placement, and design.Aside from a BASN’s inherent characteristics, designersmust consider the desired destination of sensed information.TopologyStand-alone BASNs route data for storage or for processingStar and star-mesh hybrid topologies show promise forto another location in or on the body; other BASNs movemeeting wearability, size, and data-fusion needs.7 Both thedata from the body through a gateway into other ambientstar and star-mesh hybrid topologies exploit the resourcenetworks. An example of integration with existing wirelessasymmetry (aggregator versus node) and hierarchicaltechnologies is an assisted-living facility, in which eachnature of BASNs. In a star network, all peripheral nodesresident’s BASN wirelessly communicates to a back-endconnect to the body aggregator, which allows for highmedical network. All the BASNs must maintain sufficientdata throughput and simplified routing. Having a centralQoS by cooperating to mitigate network interference andcoordinator also means having a single point of failure,transmit relevant information for further processing andhowever. To address that weakness, a star-mesh hybridpresentation. BASNs should also encrypt information totopology extends the traditional star approach and createsensure that only trusted stakeholders, such as physiciansmesh networking among central coordinators in multipleor caregivers, have access to it.star networks. The failure of a single coordinator can trigger the reorganization of nodes and coordinators withHierarchical aggregationminimal service interruption. Star-mesh hybrid topologiesData processing at the sensor node reveals informacould also link aggregators and bridge networks from thetion specific to the sensor’s locality. Information, however,body area to a wider area.might also come from relationships between data collectedat multiple sensors over time. The body area aggregatorCoordinationhas the important role of combining data from multipleStandards will help guide industry efforts by making itsensors on the body.easier to fulfill the promise of compatible and interoperThe aggregator typically possesses a richer collectionable networked technology. Fortunately, the IEEE 802.15.4of resources and a greater energy capacity than the BASNand the IEEE 802.15.6 working groups are leading the effortnodes. In addition to its role as a data fusion center, theto address scalable, body-area network coordination.8aggregator creates a bridge between the nodes and higherZigBee technology, such as the CC2420 (http://focus.ti.com/level infrastructure. It can also offer user interfacing andlit/ds/symlink/cc2420.pdf), employs the 802.15.4 Mediumcan possess its own sensing capabilities. The convergenceAccess Control protocol to allocate guaranteed time slots64computer
to specific nodes. In this protocol, the coordinator preventsnodes from transmitting during other nodes’ reservedslots. Collision avoidance and network coordination will beessential to maintaining QoS in both WSNs and BASNs.Standardizing BASNs is not easy. Because of their hierarchical nature, they exhibit significant communicationasymmetry, and all BASN nodes exist within range ofeach other, so they are likely to hear the entire network’stransmissions. Another challenge is that BASN nodes willlikely exhibit differences in transmitted data rates. Finally,BASNs that span application types, such as life-criticaland non-life-critical, must coexist, and will require somescheme for prioritizing and encrypting messages. A
These challenges have far-reaching implications but offer many immediate opportunities for system design and implementation. Although BASNs share many of these challenges and opportunities with general wireless sensor net-works (WSNs)—and can therefore build off the body of knowledge associated with them—many BASN-specific
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Laser Sensor Microphone Sensor Projectile Sensor Valve Sensor Photogate Sensor Motion/Distance Sensor Camera Shutter Sync Sensor Clip Sensor Multi-Flash Board 2. . Camera Axe 5 in a much cheaper package for the DIY/Maker crowd. Hardware The top of the both versions has a display screen, a number of buttons, a power switch (not on shield .
Laser Sensor Microphone Sensor Projectile Sensor Valve Sensor Photogate Sensor Motion/Distance Sensor Camera Shutter Sync Sensor Clip Sensor Multi-Flash Board. . Camera Axe 5 in a much cheaper package for the DIY/Maker crowd. Hardware The top of the both versions has a display screen, a number of buttons, a power switch (not on shield
SENSOR STATUS SENSOR BYPASS Press to bypass, press again to re-enable GREEN Sensor is dry RED Sensor is wet Red light indicates sensor is bypassed RAIN SENSOR BYPASS Blue/White wires to normally closed sensor terminals Orange/White wires to normally open sensor terminals 2 3 5 6 4 1 5 Wireless Rain
4. Sensor Settings pane—Set the sensor parameters in this pane 5. Status bar—Shows whether the sensor is connected, if a software update is available, and if the sensor data is being recorded to a file 6. Live Sensor Data controls—Use these controls to record, freeze, and play real-time sensor data, and to refresh the sensor connection
A sensor bias current will source from Sensor to Sensor- if a resistor is tied across R BIAS and R BIAS-. Connect a 10 kΩ resistor across Sensor and Sensor- when using an AD590 temperature sensor. See STEP 4 Sensor - Pins 13 & 14 on page 8. 15 16 R BIAS R BIAS-SENSOR BIAS CURRENT (SW1:7, 8, 9, 10)
Wireless sensor networks (WSN) Or: Wireless sensor & actuator networks (WSAN) SS 05 Ad hoc & sensor networs - Ch 1: Motivation & Applications 16 WSN application examples Disaster relief operations Drop sensor nodes from an aircraft over a wildfire Each node measures temperature
