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翻译及原⽂
重庆理⼯⼤学
⽂献翻译
⼆级学院电⼦信息与⾃动化
班级 112070102
学⽣姓名侯⼴鱼学号 11207991007
基于⽆线传感器⽹络节点的⼀氧化碳监测设计
zujue陈·詹事·秋⽉郭
发表于：20 JUNE2013
施普林格科学+商业媒体新york2013
摘要
保护环境，⼀个⽆线传感器⽹络（WSN）节点的设计⽅案，是远程监测监控⼀氧化碳的⽅法。

监控节点采⽤低功耗微处理器SSOR C8051F930作为⼀个控制器，利⽤⼀氧化碳⾦属⽜IDE （MOX）半导体传感器的检测原理是混合氧化物半导体PLE共及其树脂的氧化还原反应当加热时，⽓体浓度随⽓体浓度的变化⽽变化，在传感器、转换和处理数据等时，所收集的共信号的情况下，所收集的共信号被传送到接收器的⾼性能的⽆线射频芯⽚SI4432⽀持IEEE802.15.4通讯协议，并通过GPRS发送远程接收器的移动⽹络，实现远程监控
关键词：⼀氧化碳传感器微处理器数据处理⽆线射频芯⽚远程监控
1引⾔
⼀氧化碳是长时间吸⼊，可引起⼈体组织缺氧，最后导致窒息死亡。

设计⼀个实时监测⼀氧化碳⽓体监测系统，对⼀氧化碳的排放量进⾏检测是⾮常重要的。

在监测有害⽓体领域，国内外相关研究⼈员已经开发出⼀种⽓体传感器检测系统，⽓体检测技术已经逐渐成熟。

2010年西班⽛的Prades等设计了⼀个⽓体传感器由⾦属氧化物纳⽶材料可以快速地检测⼀氧化碳和⽔蒸⽓[ 1 ]。

2010年美国的Sazia A Eliza等，设计和硅等M进⾏⾼选择性的⽓体传感器可以监测HY -氢、⼀氧化碳等[ 2 ]。

2008年郑州航空⼯业管理学院设计的⼀种碳⽔化合物的研究对⼀氧化碳的密度分布在线检测系统采⽤单⽚机技术，CAN总线技术，实现在线监测和⼀氧化碳的浓度⼤钽实时分析和处理[ 3 ]。

2009年⽕灾科学国家重点实验室中国科学技术⼤学技术设计的⽆线⽕灾探测系统，采⽤短距离⽆线的收发芯⽚nRF2401和长距离⽆线GPRS通信模块，实现⽆线多传感器⽕灾检测[ 4 ]。

2011年太原⼤学的T型⼯程技术设计了煤矿井下探测机器⼈深深进⼊矿⼭环境完成煤炭开采区的有害⽓体检测从⽽代替员⼯完成勘探任务[ 5 ].对于⼤量的⼀氧化碳⽓体排放污染环境，由于煤的燃烧，提出的设计⽅案⼀氧化碳监测⽆线传感器节点监测⽹络使⽓体监测节点可以与⼩型化等特点，低功耗，⽆线通信，实现远程实时监测⼀氧化碳。

⼀氧化碳⽓体检测原理
2.1⽓体传感器的选择
⽓体传感器是化学传感器。

根据传感器的敏感材料与⽓体的相互作⽤机制的不同，⽓体传感器可分为半导体⽓体传感器、固体电解质⽓体传感器、接触燃烧式⽓体传感器、运算和⽓体传感器[ 6 ]，⽯英谐振式⽓体传感器、表⾯声波⽓体传感器、固体聚合物电电解质型⽓体传感器、电化学⽓体传感器。

半导体⽓体传感器可分为⾦属氧化物半导体⽓体传感器和有机半导体⽓体传感器。

⾦属氧化物半导体⽓体传感器可分为电阻式和⾮电阻。

本系统采⽤电阻式⾦属氧化物半导体⽓体传感器的温度调制实验平台。

2.2⾦属氧化物半导体⽓体传感器检测
原理
⼀氧化碳传感器的温度调制实验平台是⾦属氧化物半导体⽓体传感器，其主要成分是⾼活性⾦属氧化物SnO2烧结体。

这种类型的传感器利⽤氧化还原反应的物理现象，在与周围的⽓体浓度检测⽓体浓度的⽓体控制其电导率的变化与反应。

⼆氧化锡烧结体表⾯存在的活性粒⼦（SnO2?x）?。

当⾦属氧化物半导体加热到⼀定温度的空⽓，空⽓中的氧吸收性带负电荷的半
导体表⾯，电⼦在半导体的表⾯将被转移到吸附氧为负氧离⼦（O?，O2?）：21 O2 +（SnO2?x）?= O?AD（SnO2?x）（1）表⽰O?AD（SnO2?x）吸附在SnO2?X。

在这⼀点上，半导体表⾯上形成了⼀个正的累积空间电荷层表⾯势垒增加，阻碍电⼦流，导致材料的性能的提⾼。

在⽓敏材料，⾃由电⼦必须通过微粒的结合位点（晶界）⾦属氧化物半导体形成电⼦流，产⽣的氧屏障根吸附也存在于晶界处，阻碍了电⼦的⾃由流动，⽽这种电阻是由于传感器的电阻。

co
作为还原性⽓体，当表⾯⽓体接触该半导体时，CO和吸附氧负离⼦发⽣化学反应：
CO + O?AD（SnO2?x）= CO2 +（SnO2?x）?（2
通过氧原⼦捕获电⼦回到半导体氧化物的表⾯，与周围的环境CO浓度降低表⾯势垒降低，然后等⽓体的敏感程度材料减少。

与增强吸收⼀氧化碳，能量
I=AT2exp?qφs exp qVa?1
kT kT
的势垒电压φ和敏感材料θ表⾯覆盖由公式表达变化的关系（5）：
qN2θ2
φs=?s
2εε0Nd
其中，NS是每单位⾯积的电荷数，Nd是单位体积，供体数量的ε，ε0是半导体的介电常数，符号?”—
公式（6）表明，电导G亲portional平⽅的表⾯覆盖θ。

利⽤频率undlich吸附原理导出的关系，森—其中，K =αRTNα'，α=αexp（?KTE），的α和R是常数，B是⼀个常数与温度—
图1⼀氧化碳传感器节点的硬件设计图2传感器的硬件等效电路
3.1⼀氧化碳传感器的硬件组成
⼀氧化碳的⽆线传感器⽹络节点的硬件电路由信号调理电路、⽅法、数据处理单元、⽆线收发电路。

系统结构图1所⽰。

选择单⽚机芯⽚作为数据处理单元，内存空间的⽆线收发电路的核⼼是⽆线收发模块SI4432。

3.2信号采集与条件电路设计
传感器的硬件电路等效电路如图2所⽰。

CO传感器的温度调制实验平台具有⼀个加热过程的开端通电，将电阻加热后，将其与传感器的温度、温度、温度等进⾏改变它⼯作在敏感温度的⽓体[ 9 ]该电阻是由电压VOUT其串联电阻RL反射的关系，输出电压VOUT和半导体电阻是由图2利⽤公式计算⽓体浓度，然后⽤计算的⽓体浓度该传感器的温度对⽐实验平台的敏感是否与周围环境的温度和湿度有影响，温度和湿度有关热量补偿电路应考虑到消除影响在传感器信号检测电路设计，温度和湿度对传感器电阻的影响。

在⼀定条件下的湿度，这将弥补传感器的热量的变化使⽤⼀个热敏电阻温度。

传感器和热敏电阻应该在⼀个远离的电路，可以得到很好的补偿效应产⽣的热量的位置[ 10，1 1 ]。

信号采集和调理电路由电源控制模块、信号滤波和放⼤电路的电路，如模拟输⼊的I / O端⼝传输的模拟电压信号数据处理单元微控制器。

功率控制模块采⽤电压调节器78M05F调整10 V 到5 V的输出信号的传感器，当⼀氧化碳浓度低时，需要放⼤。

赖斯调理电路采⽤芯⽚
tmp47p443vn产⽣脉冲信号来控制加热使⽓敏电阻变化的热条件。

为了减少漂移和误差，负载电压信号由⼆阶滤波器和运算放⼤器调节，并传输到单⽚机的模拟输⼊引脚。

信号采集和放⼤等电路图如图3所⽰。

3.3数据处理单元
对于传感器信号采集和调理电路的输出电压信号，数据处理单元转换
图4输⼊/输出端⼝
C8051的1f930配置
对数字模拟，计算出相应的⽓体浓度值，建⽴了通过SPI串⾏端⼝[ 12通信模块的连续线较少的远程通信]。

除了上述功能，数据处理单元也必须读取数据和控制信息的通信模块进⾏数据融合控制的硬件平台的其他模块在⽆线传感器⽹络通信过程中，完成了协议处理和路由协议的研究。

C8051F930单⽚机是⼀种低功耗混合信号单⽚机，c8051f930具有10位A/D转换器，23个外部输⼊通道和⼀个汽车马蒂奇平均突发模式可以16位累加器提⾼A/D转换器的分辨率采样。

它保证了数据的快速、准确收集后及时处理。

I/O端⼝配置C8051F930如图4所⽰。

VOL电压输出信号的CO⽓体检测模块作为模拟输⼊连接到I / O C8051F930 P0.7引脚转换为数字/三维转换器。

模拟信号连接到I / O引脚
P0.1的内存空间。

对于这些模拟输⼊，选择0.5作为可编程增益，使⽤1.65伏作为在内部⾼速电压基准，计算相应的模拟电压的计算：
3300×ADC0
1023
C8051F930单⽚机可以读取和写⼊到内部⼯作区域的⽆线收发芯⽚SI4432通过内置的增强型SPI总线，各种参数配置灵活。

C8微处理器05 1f930采⽤4线SPI模式作为主控器件，包括MOSI，MISO，SCK 和Nsel。

MOSI⽤于传输串⾏数据由C8051F930 SI4432；MISO⽤于传输串⾏数据OM SI4432以C8051F930；SCK⽤于同步和Si4432 C8051F930单⽚机之间的串⾏数据传输；nSEL是⽚选信号。

只有当⽚选信号是低层次的，对SI4432操作有效。

3.4⽆线收发电路
SI4432⾼度集成、低功耗、多频段ISM⽆线收发器的ezradioprotm家族的⼀部分。

SI4432提供先进的⽆线功能，包括连续的频率范围从240930 MHz和⾼达20 dBm的输出功率可调。

内置天线分集和⽀持跳频可⽤于进⼀步扩⼤范围和提⾼性能。

4⼀氧化碳传感器节点软件设计
4.1信号采集的软件设计
处理模块
信号采集与处理模块的编程模型反映了A/D转换的中断函数和主函数来计算相应的电压。

ADC 内部流程图功能，如图5所⽰。

交流根据上述原理，在图5中的代码。

4.2⽆线收发模块的软件设计
⽆线收发器的软件编程采⽤模块化的设计⽅法，编程环境是Silabs IDE v4.02⽀持Keil COM编译器和汇编程序。

主要模块这个系统的编程是由主函数调⽤的独⽴函数。

该模块主要包括：初始化（包括
C8051F930、SPI、SI4432）、ADC中断功能，⽆线发送福功能和⽆线接收等功能。

⽆线发送功能负责发送数据包，包括数据加载、前导、同步字、数据负载的长度和CRC校验字节根据通信协议；⽆线接收功能是负责接收数据包并检查CRC校验字节的数据包来保证正确性收到的数据[ 13，14 ]。

该数据包在每⼀个前⾯加上⼀个前导码，可设置的长度。

要确定数据包的到达，接收器需要同步的前导码的
数据包。

同步字为标志的SYN同步模式是后序。

接收数据后，检测到同步字。

Si4432集成内部⼀些功能，如调制解调、编码/解码，所以只需设置数据加载的长度、前导和同步字的初始化时间。

（1）初始化函数：
Main()
{...while(1){
if(adc fl g==1;
{Vout=result;
Vout=Vout?3300;
Vout=Vout/1023;
EA=1;
adc fl g=0;...}...}
INTERRUPT(ADC_ISR,INTERRUPT_ADC0_EOC) {static unsigned long accumulator=0;
static unsigned int measurements=2048;
AD0INT=0;
accumulator+=ADC0;
measurements--;
if(measurements==0)
{measurements=2048;
result=accumulator/2048;
accumulator=0;
EA=0;
adc fl g=1;}
ADC0H=0;
ADC0L=0;}
图5的电路中断函数流程图
初始化函数初始化C8051F930单⽚机内部寄存器，SPI，Si4432⽆线收发频率的频率、⼯作模式、发送速率，等。

（2）⽆线发送功能
⽆线发送功能的流程图如图6所⽰。

如果数据传送成功，LED将被点亮。

代码在图6中。

RF_ENUM RFTransmit(uint8?packet,uint8length) {uint8temp8;
SpiRfWriteAddressData
(REG_WRITE|TransmitPacketLength),length);
for(temp8=0;temp8
{SpiRfWriteAddressData
(REG_WRITE|FIFOAccess),packet[temp8]);}
SpiRfWriteAddressData
(REG_WRITE|OperatingFunctionControl1),0x09);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable1),0x04);
while(RF_NIRQ_PIN==1);
ItStatus1=SpiRfReadRegister(InterruptStatus1);
ItStatus2=Sp&&iRfReadRegister(InterruptStatus2); return RF_OK;}
图6⽆线发送功能流程图
（3）⽆线接收功能
⽆线接收功能的流程图如图7所⽰。

从RX FIFO的数据送到LCD通过SPI总线的显⽰结果再接收下⼀个数据。

代码在图7中。

RF_ENUM RFReceive(void)
{SpiRfWriteAddressData
(REG_WRITE|OperatingFunctionControl1),0x05);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable1),0x13);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable2),0x00);
ItStatus1=SpiRfReadRegister(InterruptStatus1); ItStatus2=SpiRfReadRegister(InterruptStatus2); return
RF_OK;}
{xdata uint8i;
if(RF_NIRQ_PIN=0)
{ItStatus1=SpiRfReadRegister(InterruptStatus1);
ItStatus2=SpiRfReadRegister(InterruptStatus2);
if((ItStatus1&0x02)==0x02)
{?length=SpiRfReadRegister(ReceivedPacketLength)
for(i=0;i
{?packet++=SpiRfReadRegister(FIFOAccess);}
图7⽆线接收功能的流程图
5结论
通过对单⽚机数据处理和⽆线通信技术的研究，提出了⼀种低功耗的⽆线⼀氧化碳监测节点的设计传感器⽹络。

监控节点的⼀氧化碳检测范围从30 ppm⾄1000 ppm。

从理论上讲，数据传输距离可以是200⽶。

这个设计可以在将来完成：数据聚合算法，路由算法和定位算法，可以进⼀步设计。

该监控系统可实现远程监控监测煤矿井下⼀氧化碳、建筑，等。

对国家⾼技术研究发展计划（863计划）的⽀持（2006aa10z258）表⽰感谢。

作者⾮常⽀持国家⾼技术研究发展计划（863计划）（2006aa10z258）。

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原⽂：
Design of wireless sensor network node for carbon monoxide monitoring
Zujue Chen · Zhan Shi · Qiuyue Guo
Published online: 20 June 2013
Springer Science+Business Media New York 2013
Abstract Aim at protecting environment, a design proposal of Wireless Sensor Network (WSN) node for remote moni-toring Carbon Monoxide is presented. The monitoring node uses a low-power SOC microprocessor C8051F930 who acts as a controller, utilizes Carbon Monoxide metal ox-ide (MOX) semiconductor sensor whose detective princi-ple is that MOX semiconductor has redox reactions with CO and its resistance varies with gas concentration when it is heated, perceiving local CO concentration, condition-ing the collected CO signals from the sensor, converting and processing datas, etc. The datas can be transmitted to Sink by high-performance wireless radio frequency chip Si4432 which supports for communication protocol IEEE 802.15.4, and Sink uses GPRS to send them remotely to the mobile network, realizing remote monitoring CO.
Keywords Carbon monoxide sensor·Microprocessor·Data processing · Wireless radio frequency chip · Remote monitoring
1 Introduction
Carbon monoxide is inhaled for a long time,which can cause body histogenous hypoxia, finally leading to suffocation.
Z. Chen () · Z. Shi · Q. Guo
College of Computer Science and Communication Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China
e-mail: chenzujue@/doc/2b018a581a37f111f0855b4b.html
Z. Shi
e-mail: shizhan-shelly@/doc/2b018a581a37f111f0855b4b.html
Q. Guo
e-mail: hanruoxue1986@/doc/2b018a581a37f111f0855b4b.html It is particularly important to design a real-time monitor-ing system for carbon monoxide to detect carbon monoxide emissions.
In the field of monitoring of harmful gases, domestic and foreign relevant researchers have developed a number of gas sensor detection systems, gas detection technology has matured gradually. In 2010 Spain’s Prades, etc. designed a gas sensors made of metal oxide nanomaterials which can rapidly and selectively detect carbon monoxide and water vapor [1]. In 2010 U.S. Sazia A Eliza, etc. designed and sim-ulated a highly selective gas sensors which can monitor hy-drogen, carbon monoxide, etc. [2]. In 2008 the researchers of Zhengzhou Aeronautical Industry Management Institute designed a kind of carbon monoxide density distributed on-line detection system using single chip microprocessor tech-nology and CAN bus technology, realizing the concentration of carbon monoxide on-line monitoring and data real-time analysis and processing [3]. In 2009 State Key Laboratory of Fire Science China University of Science and Technol-ogy designed wireless fire detection system that uses short-range wireless transceiver chip nRF2401 and long-distance wireless communication module GPRS, realizing wireless multisensor fire detection [4]. In 2011 College of Mechan-ical Engineering of Taiyuan University of Technology de-signed a Coal Mine Detection Robot for the detection of harmful gases in coal mining areas to enter deeply into the mine environment and finish explorational tasks instead of the staff [5].
For a large number of carbon monoxide gas emissions pollute the environment because of coal spontaneous com-bustion, present a design proposal of carbon monoxide mon-itoring node for wireless sensor network so that the gas mon-itoring node can be with the characteristics of miniaturiza-tion, low power consumption and wireless communication, achieving real-time remote monitoring carbon monoxide.
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Z. Chen et al.
2 Carbon monoxide gas detection principle
2.1 The selection of gas sensor
Gas sensors are chemical sensors. According to the sen-sors’ sensitive materials and the different mechanisms and effects of the interaction with the gas, the gas sensors can be divided into semiconductor gas sensors, solid electrolyte gas sensors, the contact combustion-type gas sensors, op-tical gas sensors [6], quartz resonant gas sensors, surface acoustic wave gas sensors, solid polymer electrolyte-type gas sensors, electrochemical gas sensors. Semiconductor gas sensors can be divided into metal oxide semiconductor gas sensors and organic semiconductor gas sensors. Metal oxide semiconductor gas sensors can be divided into the resistive and the non-resistive. This system uses the resistive metal oxide semiconductor gas sensor TGS2442.
2.2 Metal oxide semiconductor gas sensor
detection principle
Electronics captured by oxygen atoms return to the sur-face of semiconductor oxide, the surface barrier decreases with its ambient CO concentration reducing, then the resis-tance of the gas sensitive material decreases. With the en-hanced absorption of carbon monoxide, the energy band of the metal oxide semi-conductor varies with the conductivity. Combine with Schottky barrier model about grain bound-ary and Freundlich isotherm adsorption principle about solid surface and gas t o derive the relationship of tin dioxide’s conductance G and measured CO’s concentration C as fol-lows. Tin dioxide semiconductor generates current under the action of the additional voltage Va:
I = AT 2
exp ?
kT
s exp kT a ? 1
(3)
q φ
q V
among which, the q is electronic charge, the V a is the ad-ditional voltage, the A is the Richardson constant, the φs is the variation of barrier voltage. Because conductance is the current’s derivation with the voltage, get the derivation as follows:
Carbon monoxide sensor TGS2442 is metal oxide semi-
d I
q φ
q
conductor gas sensor, whose main ingredient is high active
G
=
AT 2 exp
s
=
MOX tin dioxide sintered body. This type of sensor utilizes
a the physical phenomena of that MOX semiconductor has re-
AT q
q φ
dox reactions in contact with the gas and its conductivity
=
exp ?
s
(4)
k kT varies with the ambient gas concentration to detect gas con-
centrations.
The relationship of the variation of barrier voltage φs
The sintered body’s surface of tin dioxide exists many and the surface coverage of sensitive material θ is expressed
active particles (SnO 2?x ) . When the metal oxide semi-
by the formula (5):
conductor is heated to a certain temperature in the air, the q N s 2θ 2
oxygen in the air are adsorbed on the surface of negatively φs = ?
(5)
charged semiconductor. Electronics on the surface of semi- 2εε0N d
conductor will be transferred to the adsorbed oxygen into
among which, the N s is the number of charge per unit area,
negative oxygen ions (O ? , O 2?
):
the N d is the number of donor per unit volume, the ε, ε0 is
) O ?
ad (SnO 1 O + (SnO = )
(1) the semiconductor’s dielectric constant, the symbol ‘?’ in - 2 2?x 2?x dicates that the barrier reduces. The relationship of the con-
2 O ?ad (SnO 2?x ) signifies the O ?
is adsorbed on the SnO 2?x . ductance G and the surface coverage θ can be deduced by
formulas (4) and (5) as follows:
At this point a positive cumulative space charge layer which
is formed on the semiconductor surface makes the surface
AT q
exp q 2 2 θ 2
barrier increase, impeding the flow of electrons, which leads G =
N s
(6)
k
2kT εε0N d
to the increasement of the material’s resistance. Within the
gas sensitive material, free electrons must pass through the The formula (6) indicates that the conductance G is pro-
micro-grain’s binding sites (grain boundaries) of metal ox - portional to the square of the surface coverage θ . Utilize Fre-
ide semiconductor to form a flow of electrons, barrier gen- undlich adsorption principle to derive the relation of the sen-
erated by oxygen adsorption also exists at grain boundaries sitive material’s conductance G in the reducing gas and the
and impedes the free flow of electronics, which the sensor’s gas concentration C . Freundlich isotherm adsorption equa-resistance is due to. When reducing gas CO which is as the tion is:
detected gas contacts with the surface of the semiconduc- θ = KC b
(7)
tor component, CO and adsorbed oxygen negative ions have
chemical reaction:
among which, K = αRT nα’, α = α exp (?
E
), the α and
CO + O ?
ad (SnO 2?x ) = CO 2 + (SnO 2?x )
kT
(2)
the R are constants, the b is a constant related to tempera-
Design of wireless sensor network node for carbon monoxide monitoring
49
Fig. 2 Sensor’s hardware equivalent circuit
Fig. 1 The system structure diagram of WSN node for carbon monox-ide monitoring
ture. Eliminate θ by the formula (6) and the formula (7):
it work at the temperature of sensitive to the gas [9]. Af-
AT q
exp
q 2N 2K 2C 2b
A exp
B C
d
ter the R s is heated, it has adsorption reaction with carbon G
=
s
= (8) monoxide in the air, the change of metal oxide semiconduc-
k
2kT εεN
d
tor resistance is reflected by the voltage V out of its series re-
among which, A
= AT q
, B =
q 2
N s 2K
2
, d = 2b . The for- sistance R l . The relationship of the output voltage V out and
k 2kT εε0N d the semiconductor resistance R s is derived from Fig. 2, then
mula (8) gives the quantitative relationship between the sur-
calculate the gas concentration of CO indirectly by formulas
face conductance G of the sensitive materials reacting in
(9) and (10).
reducing gas and the gas concentrations C . In the circum-
stance of certain gas concentration, as the mutual adsorption
V
c ? V
out
R
l = V
, R
s = R
V
c ? V
out
(10)
effect between tin dioxide and the detected gas is affected
R
s
out
l V
out
by temperature, its electrical conductivity also have a great The sensitive of the sensor TGS2442 is influenced by the
relationship with the temperature. In the above given con- ditions and proper gas concentration range, the relationship surrounding temperature and humidity, the relevant temper- between the sensor’s resistance and carbon monoxide con - ature and humidity compensation circuit should be consid- centration can be approximately indicated by the following
ered to eliminate the impact from temperature and humidity equation:
on the sensor resistance when the sensor signal detection R s = A [C ]?α
(9)
circuit is designed. In a certain condition of humidity, it will compensate for the changes of sensor’s temperature to use among which, R s : senso r’s resistance; A : constant; C : gas
a thermistor. Sensor and thermistor should be in a position that is away from the heat generated by the circuit which can
concentration; α: slope of R s
curve [7, 8].
get a good compensation effect [10, 11].
Signal acquisition and conditioning circuit is made up of 3 Hardware design of carbon monoxide WSN node power control module, signal filtering and amplification cir- cuit, transmit the analog voltage signal as the analog input
3.1 The hardware composition of carbon monoxide WSN to the I/O port of microcontroller of data processing unit.
Power control module uses the voltage regulator node
TA78M05F to adjust 10 V into 5 V. The output signal of
Carbon monoxide wireless sensor network node hardware the sensor is small when carbon monoxide concentration is
low, which needs to be amplified. Conditioning circuit uses circuit is made up of the signal conditioning circuit collec- the chip TMP47P443VN to generate pulse signal to control tion, data processing unit, the wireless transceiver circuit. heating so that gas sensitive resistance changes in the heat- The system structure diagram is shown in Fig. 1. Select the ing conditions. To reduce drift and error, the load voltage
MCU C8051F930 chip as data processing unit while the
signal is conditioned by second-order filter and operational
core of wireless transceiver circuit is the wireless transceiver amplifiers and transmitted into the microcontroller’s analog module Si4432.
input pin. The diagram of signal acquisition and amplifica- 3.2 The design of signal acquisition and condition circuit
tion circuit is shown in Fig. 3.
Sensor’s hardware equivalent ci rcuit is shown in Fig. 2. The sensor TGS2442 for CO has a heating process at the be-
ginning of energization, the heating resistor Heater pack-aged together with it changes sensor’s temperature, making
3.3 The data processing unit
For the output voltage signal of sensor signal acquisition and conditioning circuit, the data processing unit converts
50Z. Chen et al. Fig. 3 Signal acquisition and
amplification circuit
Fig. 4 The I/O ports
configuration of C8051F930
the analogous to the digital, calculates the correspond-ing gas concentration value, establishes a continuous wire-less remote communication with a communication module through the SPI serial port [12]. In addition to the above features, data processing unit must also read the datas and control informations from communication module for data fusion control the other modules of the hardware platform, complete the protocol processing of MAC and routing in the process of WSN communication.
C8051F930 is a low power mixed-signal MCU of SOC.C8051F930 has a 10-bit A/D converter, which has 23 external input channels and a 16-bit accumulator for auto-matic averaging with burst mode which can increase A/D convert er’s resolution by oversampling. It ensures to collect the datas rapidly and correctly after the sudden rouse. The I/O ports configuration of C8051F930 is shown in Fig. 4. The voltage output signal of CO gas detection module as analog input connects to the I/O pin P0.7 of C8051F930 and is converted to the digital by A/D converter. The analog ground signal connects to the I/O pin P0.1 of C8051F930. For these analog inputs, select 0.5 as the programmable gain, use 1.65 V as the internal high-speed voltage reference, cal-culate the corresponding analog voltage:
V 3300 × ADC0 (11) 1023
out =
C8051F930 can read from and write to the internal reg-ister of the wireless transceiver chip Si4432 by the built-in enhanced SPI bus, configuring flexibly various parameters. The microprocessor of
C8051F930 uses 4-wire SPI mode as the master device, including MOSI, MISO, SCK and nSEL. MOSI is used to transmit the serial datas from C8051F930 to Si4432; MISO is used to transmit the serial datas from Si4432 to C8051F930; SCK is used to synchronize the serial datas transmission between the C8051F930 and the Si4432;
Design of wireless sensor network node for carbon monoxide monitoring 51
nSEL is the chip select signal. Only if the chip select signal is the low level, the operation on the Si4432 is valid.
3.4 The wireless transceiver circuit
Si4432 highly integrated, low power, multi-band wireless ISM transceiver is part of the EZRadioPROTM family. The Si4432 offers advanced radio features including continuous frequency coverage from 240 to 930 MHZ and adjustable output power of up to +20 dBm. Built-in antenna diversity and support for frequency hopping can be used to further extend range and enhance performance.
4 Software design of carbon monoxide WSN node
4.1The software design of signal
acquisition and processing module
The programming of signal acquisition and processing mod-ule reflects in the A/D conversion interrupt function and the main function to calculate the corresponding voltage. The flow chart of ADC interrupt function is shown in Fig. 5. Ac-cording to the above-mentioned theory, the code is in Fig. 5.
4.2 The software design of wireless transceiving module The software programming of Wireless transceiver uses the method of modular design, the programming environment is the Silabs IDE V4.02 which supports the Keil com-piler and assembler. The major modules of this system are programmed independent functions called by the main function. The modules include: initialization (including
C8051F930, SPI, Si4432), ADC interrupt function, wireless sending function and wireless receiving function and so on. Wireless sending function is responsible for transmitting the packet including data load, preamble, sync word, the length of the data payload and the CRC checking byte according to the communication protocol; wireless receiving function is responsible for receiving the packet and checking the CRC checking byte in the packet to ensure the correctness of the received data [13, 14].
The packet adds a preamble in front of each one, the length of which can be set. To identify the packet’s arrival, the receiver needs the preamble to synchronize the packet. Sync word as a sign of synchronization pattern is after the preamble. The receiver starts to receive datas after the sync word is detected. Si4432 integrates internally some func-tions such as modulation/demodulation, coding/decoding, so just set the length of the data load, preamble and sync word at the time of initialization.
(1) Initialization function Main ()
{ . . . while (1) { if
(adcflg = = 1;
{V out= result;
V out= V out3300;
V out= V out/1023;
EA = 1;
adcflg = 0; . . . } . . . }
INTERRUPT (ADC_ISR,INTERRUPT_ADC0_EOC)
{ static unsigned long accumulator = 0;
static unsigned int measurements = 2048;
AD0INT = 0;
accumulator + = ADC0;
measurements--;
if (measurements ==0)
{ measurements = 2048;
result = accumulator/2048;
accumulator = 0;
EA = 0;
adcflg = 1;}
ADC0H = 0;
ADC0L = 0;}
Fig. 5The flow chart of ADC interrupt function
The initialization function initializes C8051F930, SPI, Si4432 internal registors about wireless transceiver fre-quency, working mode, sending rate, etc.
(2) Wireless sending function
The flow chart of wireless sending function is shown in Fig. 6. If the datas are transmitted successfully, the LED will be lightened. The code is in Fig. 6.
RF_ENUM RFTransmit (uint8 ?packet, uint8 length) { uint8 temp8;
SpiRfWriteAddressData
(REG_WRITE|TransmitPacketLength), length);
for (temp8 = 0; temp8 < length; temp8++)
{ SpiRfWriteAddressData
(REG_WRITE|FIFOAccess), packet[temp8]); }
SpiRfWriteAddressData
(REG_WRITE|OperatingFunctionControl1), 0x09);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable1), 0x04);
while (RF_NIRQ_PIN == 1);
ItStatus1 = SpiRfReadRegister (InterruptStatus1);
ItStatus2 = Sp&&iRfReadRegister (InterruptStatus2); return RF_OK; }
ig.6The fl ow chart ofwireless sending function
(3)Wireless receiving function
The fl ow chart of wireless receiving function is shown in Fig.7.The data from RX FIFO is send to the LCD by SPI bus to display the result and then receive the next data.The code is in Fig.7. 5Conclusion Through the study on MCU data processing and wireless communication technology,present a design proposal of a low power carbon monoxide monitoring node for wireless RF_ENUM RFReceive(void)
{SpiRfWriteAddressData
(REG_WRITE|OperatingFunctionControl1),0x05);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable1),0x13);
SpiRfWriteAddressData
(REG_WRITE|InterruptEnable2),0x00);
ItStatus1=SpiRfReadRegister(InterruptStatus1); ItStatus2= SpiRfReadRegister(InterruptStatus2); return RF_OK;}
{xdata uint8i;
if(RF_NIRQ_PIN=0)
{ItStatus1=SpiRfReadRegister(InterruptStatus1);
ItStatus2=SpiRfReadRegister(InterruptStatus2);
if((ItStatus1&0x02)==0x02)
{?length=SpiRfReadRegister(ReceivedPacketLength)
for(i=0;i
{?packet++=SpiRfReadRegister(FIFOAccess);}
Fig.7The fl ow chart of wireless receiving function。