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Temperature monitoring based on wireless communication system design

In Electronic Infomation Category: T | on March 18,2011

Abstract: SCM technology and M66005-0001FP datasheet and wireless sensor network technology, introduces the hierarchical structure of a wireless communication with the temperature monitoring system, and M66005-0001FP price and designed based on this hierarchical structure of communication protocol, given the system hardware architecture and M66005-0001FP suppliers and software design. The application results show that the system can be widely applied in areas of need for temperature monitoring.

1 Introduction

Temperature and is closely related to peoples production and life, the need for temperature monitoring of the situation very much. Traditional wired routing complexity of the existence of temperature measurement methods, the line is easy and aging issues. Wireless temperature measurement compared with wired temperature measurement, a low cost, easy to carry, so simple and quick to build the network, especially in the wired network is not smooth or environmental factors limit the field lines across the case of inconvenience, the use of wireless communication temperature monitoring technology even more practical and efficient.

Wireless sensor network technology in the 21st century has been greatly developed, the typical sensor network is defined by a large number of homogeneous, tiny, resource-constrained, the basic dynamic of the sensor nodes are not randomly distributed in the formation of the measured area the large-scale, self-organization, multi-hop, unpartitioned network.

In some occasions we do not need to build large-scale, self-organizing network, combined with wireless sensor networks, this paper presents a layered structure with the temperature monitoring system for wireless communications, and gives it kind of hierarchical structure of the communication protocol, the system draws on the characteristics of wireless sensor networks also need not consider sensor network self-organization of network construction, reducing power consumption.

2 system structure

Reference to the wireless sensor network clustering structure to reduce power consumption for the purpose of this paper, the structure has two temperature monitoring based on wireless communication systems, system consists of a large number of wireless sensor nodes, secondary nodes and a master nodes. System structure shown in Figure 1, the master node M is equivalent to a wireless sensor network cluster head, is also the master node. 1,2, ... ..., N is equivalent to the wireless sensor network in the first two clusters, the paper referred to as the secondary node, A1, A2, ... ..., Am for the second child of node 1, B1, B2, ... ... , Bm for the two child nodes of node 2, N1, N2 as the secondary node Ns child nodes and so on. Distributed sensor network node cluster head node is mainly used for receiving sensor data reporting, and its fusion processing. Master node M of the system is not energy limited, mainly responsible for the collection and coordination of all child nodes of the data and upload to the monitor after the host. Two each sensor node is responsible for collecting data on child nodes, and is responsible for receiving and orders issued by the master node, in transit from the role of the entire structure. Child nodes of the sensor is mainly used with the RF transceiver temperature acquisition and transmission. To save energy, the underlying sensor nodes operating in sleep - listening mode, only the second node receives the data request command to transfer data only.

Figure 1 System structure

Master node and monitoring the computer through the serial port communication, the two nodes to be placed in close proximity with the location of the master node, the sensor sub-nodes placed randomly. The low-cost RF transmission systems, power consumption, using two layers of communication solutions to meet the more remote temperature monitoring.

3 system hardware design

3.1 sensor node hardware design

A complete sensor nodes need to have small size, low power, short-range communication features, so that a sensor node typically consists of sensors modules, processor modules, wireless communication module. Sensor nodes of the system hardware architecture shown in Figure 2.

Figure 2 sensor node hardware structure DALLAS

temperature sensor produced DS18B20, DS18B20 has a unique single-bus interface, can communicate only one interface pins, and can exist in multiple DS18B20 bus with a single measurement range - 55 to 125 , with 9-bit digital value and read out the temperature, very few external components needed, small size, to meet the requirements of sensor nodes. MCU is Atmel Corporation

ATmega16L AVR-based enhanced R ISC structure of low-power CMOS 8-bit micro-controller.

Atmega16L data throughput of up to 1M IPS / MHz, thus easing the system power consumption and processing speed in the contradiction between, there are six sleep mode, and 1MHz, 3V, 25 in the normal mode when the power is 111mA, idle mode is 0135mA, suitable for low power requirements of sensor nodes.

Wireless communications chip company NRF905 Nordic wireless transceiver chip. NRF905 is a work in 433 / 868 / 915 bands, programmable single-chip RF transceiver, small size, simple peripheral circuits, high integration. NRF905 prefix can be automatically completed and the CRC (cyclic redundancy check), will be on-chip hardware automatically Manchester encoding, decoding, using the SP I interface with micro-controllers. Very low power consumption, to - 10 dBm transmitter output power when the current is only 11 mA, during receive mode current is 1215 mA. The main feature is programmed by microcontroller chip NRF905 assigned to each address, the address width of up to 4 bytes.

Temperature sensor node is responsible for the collection and wireless transmission, the sensor data collected DS18B20 will send Atmega16L, At2mega16 mouth of the data sent through the SP I NRF905, then NRF905 after the data package sent to the secondary node.

3.2 master node and secondary node hardware design

Master node and secondary nodes of the hardware structure shown in Figure 3, the processor is using a low-power microcontroller ATmenga16L, launching the companys NRF905 Nordic chip wireless transceiver chip, a difference is the master node and monitoring via RS232 computer communications, the master node to collect the data from each sensor nodes simply sent to the monitor after the computer, monitoring computer responsible for data preservation and temperature display.

Figure 3, two nodes and master node hardware architecture

4 Communication Protocol

System uses a hierarchical structure as shown in Figure 1, the master node work with data requests, by order of the data on the secondary node request, the second node receives the data request command, the collected data to the main nodes centrally, the master node to address with the temperature sensor data to the host computer. NRF905 can only receive 32 bytes of data, so the bottom is not an infinite number of sensor nodes, according to DS18B20 communication protocol, DS18B20 collected temperature data is two bytes, and each sensor has only 1 byte address, so that each sensor node sent to the secondary data is three bytes, or two bytes of the temperature data and one byte of the address data. Two nodes transmit a maximum of 32 bytes of data, in order to ensure the stability of data transmission, the system corresponding to each secondary node 10 low-level sensor nodes, a total of 20 secondary nodes constructed, the system underlying the total number of sensor nodes is 200. All nodes of the system are of the same communication channel, when there is simultaneous transmission of data over the case of the node, it will lead to the formation of mutual interference between the received data is not correct, therefore need a mechanism to channel a reasonable allocation of resources, reduce data conflict. Based NRF905 communication features that the two NRF905 modules with the same frequency band necessary to communicate successfully and address the design of communication protocols, communication protocol algorithm is as follows:

(1) the master node M using polling data requests work, according to the order of data requests on the secondary node, the master node for each secondary node after sending the command request data channel will enter the listening state, a certain time slot T, the master node has been in a state of listening channel.

(2) two-channel listening node to receive data requests from the master node commands, data requests received after the end of the listen command, sends a reply message.

(3) the secondary master node M with similar work, according to the order of data requests to the sensor nodes, secondary nodes for each sensor node sending the requested data will be entered after the command channel listening state, a certain time slot within the two nodes Tm channel state has been in listening.

(4) sensor nodes listening channel, receiving data from the secondary node request command, the command received after the end of the listener, send temperature data.

(5) the secondary node and sensor node for data transmission and reception of data packets.

(6) the primary node and secondary nodes for data transmission and reception of data packets from the second node.

(7) monitor the primary node and host communication, each sensor node to send the temperature data acquisition and sensor addresses.

Wireless transmission of data in the system must have a uniform format, the data packet format is as follows:

Which the preamble is automatically added by the device, take a byte; destination address is the packet to reach the destination address, and occupation of a byte; data attributes used to describe the packet is a packet or a command packet , is one byte; valid data collection, including the node information and address information can be set to a maximum of 32 bytes; CRC check done automatically, the system uses 16-bit CRC checksum takes 2 bytes. Communication issued by the master node

packet format is as follows:

Where the destination address is the address of the secondary node, the command word is the command to request data, the data request command with 0AH representatives, one byte, the effective data length is empty.

Secondary node response packet format is as follows:

Whose destination address is the address of the primary node, use the word 0BH response that takes 1 byte, the effective data length is empty.

Two nodes with a given collection point data packet format is as follows:

Destination address is the primary node where the address, data, signs with 0CH that one byte, the effective length of the data including the temperature sensor data and sensor node address data, taking up 30 bytes.

System, all nodes work in the same channel, same time only two nodes in communication, and only the primary node of a node in a data communications requirements will be connected, other times not connected the two sides are in a state of and communication protocols for efficient data to avoid conflict, reduce process flow chart in Figure 4 the master of low system power consumption.

master program flow chart in Figure 4

5 software

Follow the communication protocol, the system software includes the master node of the program design, the secondary node, and the underlying programming sensor programming. Master node is responsible for the coordination of the entire system, the systems data request commands are issued by the master node, the data are also a summary of the final completion of the master node. Two nodes from the transit procedures in effect throughout the system, the underlying sensor is only responsible for data collection and transmission. Follow the communication protocol, each node of the program during the design of the system to have a unified plan, the system is in addition to the master module outside of each NRF905 assigned a different address, the entire system a total of 220 NRF905 modules, corresponding to the 220 address, the address configuration is the key to achieving the communication protocol. NRF905 communication is characterized by two NRF905 module has the same frequency band necessary to communicate successfully and address, which address more than 200 different modules to communicate successful software process must be strictly observed, and apart from each other than the master node at boot time NRF905 have been configured with a unique address, and set to receive mode.

Master programming is the key to the communications, the secondary node the primary node software design and programming the same. Master program flow chart shown in Figure 4, the master node controller initialization NRF905 module configuration NRF905 Node 1 address is the address of the secondary, the main controller is set to launch NRF905 mode, send the data request command, because the master node configuration is the address of the secondary node 1, the master node sends the data request command, node 1 can receive only two, the other two nodes not receiving, point to point communications realized. Completion of the master node sends a data request command, enter the wait state 1, the secondary node receives the response message from the received response message wait state after the end of 1, 2, waits to receive data packets from the second node, to close After the end of the packet wait state 2. After entering wait state node if the node does not receive the response from the secondary information or data packet will automatically end waiting for a certain time delay. Master node controller reset NRF905 second node address is the address of 2, repeating the process a second node of each completed acquisition of data packets, the master node controller, the address must be reset NRF905 node address for the next two , and so on until a complete secondary nodes collect the data, the main controller through the serial port to transfer all data to the monitoring host, transmission is completed the controller to reconfigure NRF905 emperors address to the next round of data collection. Accordance with the above process, the master node controller 20 to store the address of the secondary node, which is the key to polling communications.

6 Conclusion

This paper, a cluster-like structure with two layers of the temperature monitoring system for wireless communication, communication protocol is simple and reliable, the system draws on the characteristics of sensor networks and sensor networks need to consider the construction of a similar network design, greatly reduce energy consumption. Simple structure, small size, the system can be widely used in greenhouses greenhouse temperature, grain temperature monitoring, power switching temperature and other fields.

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