| In recent years, the appearance of wireless sensor network which is a hot subject makes sensor itself a richer, more powerful processing, more micro volume and lower device costs and power consumption device. So it has broad application prospects in military, civilian, industrial production and other fields. It is known as one of the 21st century's most influential technology and the 10 technology which will change the world.Wireless sensor network node is a typical example of embedded systems which is composed of sensor, processor, wireless communication and energy supply modules. It follows the general design principles of embedded system. The principles are that hardware and software can be trimmed and meet the stringent requirements in functionality, reliability, cost, size, power consumption and other aspects. In practical application, the sensor nodes need to complete the collection and conversion of the monitoring data, data transmission and control, or even handle compression and decompression, encryption and decryption and other tasks. But the capacity of batteries-powered are generally not large enough and most of the nodes work in harsh environment or the area in which there is no human. It isn't able to recharge the batteries or change them so once the battery power is used up that means the nodes will lose its role. Therefore, low-power has become the core of the research.When the wireless sensor network nodes are running in the network, the energy comes mainly from three operations that are processing, sensor and wireless transmission. The energy consumption of processing is mainly due to the implementation of microprocessor instructions. Processor has large difference in energy consumption when it is activated or in a state of sleep. The energy consumption of sensing including converters, front-end processing, A / D conversion operation. It is different with the different sensor types. And wireless module may be at the four states: sending, receiving, leisure and sleep. The power instructions of the four states are not the same. Wireless module is the main energy source, the power instructions at leisure state almost equal to the receive state. In order to save energy, we should make wireless module sleep as far as possible.Considering the energy loss links of wireless sensor network node, this paper gives low-power design and research mainly from two aspects hardware and software. For hardware we should try to choose low-power and high integration chips which have rich on-chip resources, choose large capacity batteries as power supply, use a lower voltage and frequency as far as possible and low-power components and structure of the circuits. This paper compares various modules and chips in the market and selects MSP430F149 ultra-low power MCU and CC2420 RF chips as the preferred according to the functional requirements of wireless sensor network nodes. MSP430 MCU uses 1.8 V to 3.6V voltage as the power supply voltage. The power consumption is only 0.1 uA in RAM data retention mode and 250 uA / MIPS in activities mode, but the traditional MCS-51 MCU is 10 uA ~ 20uA / MIPS. The maximum input leakage current of MSP430 MCU is only 50 nA, but MCS-51 is generally 1 to 10 uA. The work frequency range of CC2420 is 2.4835 ~ 2.400 GHz; It has strong ability to dispute the interference from near channel (39 db), ultra-low current (RX: 18.8Am, TX: 17.4mA) high receiver sensitivity (-94 dbm), integrated VCO, LAN, PA and power rectifier and a low power supply voltage (2.1 to 3.6 V). We choose new ultra-low power memory FM24CL16. It can be data retention when there is no power, has high read and write speed, parallel port access speed of 70 ns, 20M serial clock speed, no 10 ms'waiting time and a standby current of less than 1 uA, write current is less than 150 uA and can be erased almost unlimited number of at least 100 million times. We use energy-saving MOS switching circuit in the sensor module and a zero-power WG Series magnetic WeiGen sensor in the instrumentation field in which wireless sensor network is applied widely. For portable devices, the power supply system is essential and is composed of LDO and batteries. The paper studies on the performance of various batteries and selects the economic and applicable No.5 high-octane alkaline batteries. And chooses ultra-low-power and ultra-low dropout TPS76927 as LDO, ultra-low dropout ensures that when the batteries'voltage drop to close to 2.7 V the system can still obtain stability system work voltage, so the battery can be fully used. At the end part of the hardware design also present some specific application examples in different nodes with a number of low-power technologies. Such as application of zero-power electromagnetic valve, improvement of valve states detection circuit and ultra-low-power design of embedded real-time clock.The software measures include the choice of low duty cycle mode and dynamic power management: when the system doesn't work, let system enters sleep mode in order to reduce energy consumption; short-range wireless communications technology ZigBee protocol based on the IEEE 802.15.4 standard and TinyOS embed operating system which is suitable for wireless sensor networks: ZigBee protocol has some advantages such as low power consumption, low transmission rate and low cost, until now it is the one of the preferred technology using in wireless communications applications in wireless sensor networks; and reasonable design of dormancy scheduling mechanism.The paper also do a series of experiments about nodes that made based on the design above, including MCU module, RF communications module and the measure of the battery capacity. And obtain effective and convincing experimental data: current consumption about MSP430 MCU module of the node system is 295 uA when the MCU is working and is 30 uA under sleep mode 3; the working current of CC2420 module is 17.4 mA when receiving data, is 18.8 mA when sending data and is 1 uA at sleep mode; the working current of the entire system is about 18.4 mA when collecting ,receiving and sending data, and current consumption of dormancy is 31 uA; total capacity of three batteries in tandem can be used is 2779.5 mAh. We can get the conclusions by compute these experimental data: the service life of wireless sensor network nodes can be increased to about eight years based on the low-power hardware design and reasonable software mechanisms that given in this paper, and can meet the application requirements of various filed in great extent. |
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