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ECGR-6185Advanced Embedded SystemsWireless Sensor Network for pH SensingSushant SenguptaSensor Network for pH Sensing• Introduction.• Architecture.• Working.• Application.Introduction• An aqueous sensor network is described consisting of an array of sensor nodes that can be randomly distributed throughout a lake or drinking water reservoir.• The data of an individual node is transmitted to the host node via acoustic waves using intermediate nodes as relays.• Each node of the sensor network is a data router, and contains sensors capable of measuring environmental parameters of interest.IntroductionThree types of nodes:-• General nodes: They are simply dispersed in water.• Host node: It is placed on land & physically connected to a computer and uses a RF transceiver for wireless communication.• Uplink node: The uplink node (floating green sphere) transfers information across the water/air boundary, using a RF transceiver to communicate with the host node, and acoustic transducer to communicate with the submerged nodes.Introduction• The nodes (blue spheres) are scattered throughout the lake and communicate acoustically (red lines).• The uplink node (green sphere) contains both an acoustic transducer, and a RF transceiver through which it communicates to the host node (black sphere) that is directly attached to a computer.Block DiagramExplanation of Block Diagram• The critical components are the main controller module that oversees the sensor node operation.• The acoustic transducer interface circuitry that amplifies and modulates the output and input signal to/from the transducer.• The sensor interface circuitry that converts the raw sensor signals to digital information, and the power supply.Explanation of Block Diagram• Although the nodes can be equipped with different types of sensors in this work they are equipped with magnetoelastic sensor arrays to monitor ambient pH. • The host node contains only a RF transceiver, and communicates with the computer via RS232 protocol.• The uplink node contains both RF and acoustic transducers, while the rest of the nodes contain only acoustic transducers.The Sensor NodeThe Sensor Node• The circuit modules and batteries are mounted on a frame that slides into the protective frame made of PVC pipe.• Before deploying the sensor node is sealed and connected to a concrete block acting as an anchor.• The acoustic transducer is mounted inside a PVC cap, with its front end exposed to water.The Sensor Node• The magnetoelastic sensor array is mounted within an open pipe, fitted through a 3 cm in diameter PVC cap, through which water flows.• A 100-turn loop of 40 gauge wire is wrapped around this open pipe, creating in effect a solenoid, which is used to transduce sensor information.Aqueous Sensor Network Design•The nodes are represented by red spheres.•The communication links represented by blue lines.Aqueous Sensor Network Design• To establish a network, the host node first sends out a broadcast signal containing its identity, which is 4.• The signal is modulated using on-off modulation scheme.• The data is encoded with one-byte-to-twelve-bits conversion before transmission.Aqueous Sensor Network Design• The broadcast signal format is:Aqueous Sensor Network Design• The first byte of the broadcast signal is Preamble, which is always CC in hex decimal. It is used for the receiver to synchronize (lock) to the frequency of the signal.• The preamble is followed by Start, which is always C0, to indicate the beginning of the actual data.• the Length field shows the length of the data. • Since the host does not know the specific target of its initial broadcast transmission, the To field of the data is set to zero.Aqueous Sensor Network Design• The identity of the node is stored in the From field.• The Command field is set to 01 indicating this is a broadcast signal. • The Level field indicates the number of nodes this broadcast signal has passed through, with the host node starts at 1.• The Checksum field is used for error detection.Aqueous Sensor Network DesignAn acknowledgement signal back to the host to indicate that the node has received the host’s broadcast signal:Aqueous Sensor Network Design• The Preamble, Start, Length, From, To, and Checksum fields are identical to the broadcast signal.• In the Command field, ‘3’ indicates this is an acknowledgement signal and the X in Command field is the sequence number, which is toggled between 1 and 0 per each successive transmission. • The sequence number is important for the node to know if its acknowledgement signal is received correctly by its parent node.Aqueous Sensor Network Design• Note that when Node 6 sends out a broadcast signal, Node 3, which is at the same hierarchical level as Node 6, will also receive it.• To avoid confusion each node is programmed to accept only signals from a node of higher level.• Hence, the broadcast from Node 6 will be ignored by Node 3 and the host node.Aqueous Sensor Network Design• After all nodes know the identity of their parent nodes, they will acquire sensor data and transmit it at a predetermined time interval. The relayed sensor data has the form of:Aqueous Sensor Network Design• The Preamble, Start, Length, To, From, and Checksum are identical to the broadcast signal. • The ‘2’ in Command field indicates this transmission contains sensor data. • To know the origin of this sensor data, The Data field starts with the identities of the nodes that relay the data, followed by a byte of zero, and then the actual sensor data. • For example, when Node 6 relays Node 7 data to Node 4, the• Data field is:pH Sensing• To measure pH independently of background salt concentrations, one sensor element is coated with poly(3-sulfopropyl methacrylate-co-isooctylacrylate), abbreviated pSPMA-IOA, a strong polyelectrolyte gel the swelling/shrinking of which is dependent on solution salt concentration and independent of pH.• Another magnetoelastic element is coated with poly(acrylic acid -coisooctylacrylate), abbreviated pAA-IOA, a pH responsive polymer described earlier that also responds to ambient salt concentration levels.• Cross correlation between the frequency responses of the polymer coated magnetoelastic elements enables an absolute determination of pH.pH Sensing• A sensor interface circuit is used to convert the measured resonant frequency of a


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UNCC ECGR 6185 - Wireless Sensor Network for PH Sensing

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