Development of a Cost Effective Wireless Sensor System for Indoor
Contents
1. pe RR A eap eam eap enpe Pe Rm id ls in in ni i mt ha i 1 1 1 D 1 1 1 s sak ks 1 1 mal 1 1 1 ERE a EE s 1 1 1 mama mm dmm ami 1 1 1 1 1 1 1 q o o o o o o ee i H i 1 sadaa decdec desleal B 1 lcd odds pore Cat rat LA decdocdo Lolo li lil il il El Ei A da rrr Pree Ct cet Cat cet eet O aod Bos an E a e 1 D 1 T gu en mm ap Ed D T D D D D 4 F i gt rP 7 T 4 E i i 1 1 T 4 M T r 7 T 1 i i T 1 1 1 1 i Li EE e ela L sb Li E La T l L A4 d L L 4 t 1 5 07 Ep ee A o q e app A ee a s tA MIR Mm mm penam ae on rm s L Rs k ko sebscksebzakze 1 1 L 4 1 sdssds gee A als wade sd ss es des dass 4 12 isa e o nee o kas usa il kas id Pek eae Val A Sol Ll AT ee Mec pete mt iR Rm ARR TP RR iR AAA RE RE sg E I L apes whe le ee ee dis ee ee 15 57 14 57 v 14 13 il oF 11 57 12 07 12 67 13 4 15 57 13 oF T EW 1 a Wiel Figure 3 12 Output voltage vs input voltage of the heat Y vi t ing circui2. A ee ee ee ee gt jaguar jan gt ap a y MRE 3 4 t6 TT t AR P ees is r w O 7 R MN 1 y T 1 T T T T T n 4 e E x v g Kas _ a ds ts co Du Jee decdect H E UD A dice O DE E TE A RA A Wu ond M desdes Lee i i i i i i i oe E A AO A PE A E E E E ks Lot A AP CU H M cda n D E E QE A NS O T PAP A H ROPA J day o sy a ee ee A L a eer E du ed 9 sss f C L Ab robs N R F 3 7 o 4 F q r LI r g 7 a i P r jane i gt een n u M MENS i La 4 1 1 i gt ou E a i 4 s EN A O PR i wee a su ow imd i a Sa eS aul sdasdesiesiaejsamadasdaeatbkest aaa das bam boo MEM L CENE S PE 412 k a L z a ERA PR En U S FE O Lk kh EE AA a i EMEN amp ake Gow don sd wet cok s c A ES Bee Soe o H shes ok lah disci ru i b al O UD 4 H ho A A OR A A AN AA H _ SES M tH i gt G ZA S A A A P een O A DIT SA ee jane r P ees F A i t lt t r dnd EE y H Mr 1551 15 07 7 5V7 1 07 8 5V 9 97 9 57 10 97 15 5V 11 0V 11 5V 12 97 12 57 13 07 13 57 14 07 14 57 TW IN 1 01 t current inpu v vi 3 13 Input voltage vs Figure 20 3 4 1
3. MEN Eni Figure 3 28 Experimental setup 1 Figure 3 29 Experimental setup 2 similarly regulated voltage of 1 42 V was obtained for input voltages of range 7V to 15V when the control voltage was set as 5V as in Figure 3 29 33 The control voltage was varied from 0V 5V keeping the input voltage of 15V The output voltage remained at 1 42 V when control voltage was varies from 0 to 0 7V It changed to 4 92 V when the control voltage was above 1 0V 34 CHAPTER 4 DESIGN AND DEVELOPMENT OF SENSOR NODE MODULES 4 1 Introduction The sensor node module we developed 1s equipped with multiple sensors a processing unit a wireless communication module for receiving and transmitting various sensed signals and commands and an adapter for power supply The processing unit is Arduino Uno a microcontroller board based on Atmega328 Wireless communication is achieved by using the Xbee module For placing multiple sensors with their conditioning circuits Sensor Shields were designed The side view of the sensor node is shown in the Figure 4 1 The main components of the node are Arduino board Xbee shield Xbee and the sensor shield The Xbee module and sensor shield are placed on the Xbee shield This Xbee shield 1s mounted on top of the Arduino board Figure 4 1 Block diagram of sensor node module Several factors like cost power consumption space utilization was considered for the design of the module We have pu
4. 3 4 3 Heating Circuit for Ozone Sensor 3 4 3 Design The heating requirements for ozone sensor are 5V and 180 mA approximately The regulator has a maximum current capacity of 1 5A This sensor needs the same voltage as that for VOC Sensor Hence the heating circuit design was similar to that of the VOC sensor Therefore R1 240 ohms R2 680 ohms and R4 36 ohms The design circuit with the heating resistor of ozone sensor as load R3 1s shown in Figure 3 19 U1 LM317K IN ZOUT u lout Vout R3 31 Figure 3 19 Heating circuit for ozone sensor 25 3 4 3 2 Simulations The graphs of input voltage vs output voltage and input voltage vs input current were plotted in Cadence PSpice In the Figure 3 20 it was observed that a constant voltage of 5 01 V was obtained when input voltage was varied from 7V to 15V EAU 4 2 8 ANT A q A A I yr 7 5 7 57 A DY 8 5V 3 3 5V 1 0 14 54 11 07 11 54 12 0V 12 5V 13 07 13 51 14 0 14 5V 15 V gt VIIDUTI v n Figure 3 20 Input voltage vs output voltage From the graph in Figure 3 21 the current consumption was observed to be a constant of 166 6 mA when input voltage was varied from 7V to 15V 26 167 mA 166 ImA 1665 2mA 165 8m 165 ba uv 1 3V 8 uv y SV 9 uv 9 9V 10 0v 10 5 11 04 11 54 12 0V 12 54 13 FV 13 5V 18 DV 18 5V 15 UV 3 I 01 IB Figure 3 21 Input voltage vs input current
5. 26 Wan Rong Kong Dequan Analysis on Influencing Factors of Indoor Air Quality and Measures of Improvement on Modern Buildings Bioinformatics and Biomedical Engineering 2008 ICBBE 2008 The 2nd International Conference on vol no pp 3959 3962 16 18 May 2008 doi 10 1109 ICBBE 2008 492 27 Gaudioso M Khalaf W Pace C On the Use of the SVM Approach in Analyzing an Electronic Nose Hybrid Intelligent Systems 2007 HIS 2007 7thInternational Conference on vol no pp 42 46 17 19 Sept 2007 doi 10 1109 HIS 2007 16 28 Sensors and Actuators B Chemical Toward innovations of gas sensor technology http www uta edu rfmems BMC 0720 0902 backup Background Toward 20innovations 200 f 20gas 20sensor 20technology pdf 29 Chirag Borkar Development of Wireless Sensor Network System for Indoor Air Quality Monitoring Master s Thesis December 2012 30 Pengpeng Chen Zhanming Lu A Web Based Indoor Environment Monitoring System Using Wireless Sensor Networks Computational and Information Sciences ICCIS 2013 Fifth International Conference on vol no pp 2007 2010 21 23 June 2013 doi 10 1109 ICCIS 2013 529 69
6. 58 A similar procedure done for CO2 estimation was carried out for this one also By minimizing the least square error we get 0 H H H x Solving for 0 we get a 1 3813 and b 1555 9 Hence the conversion formula 1s y n 1 3813xV n 1555 9 Estimated VOC concentration in ppb unit Then voltage values were put in this equation to see if it matches with the concentration measurement from Graywolf Sensor The Figure 6 11 shows the estimated concentration y n from our system and concentration x n taken from Graywolf system raywolf e Estimated m Ke Q c a Q gt v DD No of Readings Figure 6 11 Estimated VOC concentration and the Graywolf measurement Experiment 2 6 3 2 Conversion formula for the CO Sensor The signal model for the CO sensor was taken the same as that of VOC sensor y H0 a Vector parameter 0 El here a and b are the unknown parameters Observation 59 matrix H V 1 0 V is the matrix for sensor output voltage millivolts By minimizing the least square error the parameters are calculated 0 H H H x Solving for 0 we get a 20 017 and b 36 14 Hence the equation for estimated CO concentration y n 0 017xV n 36 14 Estimated CO concentration in ppm unit The Figure 6 12 plots the estimated concentration y n and concentration x n taken from Graywolf system Graywolf e Estimated MN c Oo m OO DO No of Rea
7. 3 4 3 3 Experiments and Tests The power is provided using a power supply and measurements was taken using a multimeter A constant output voltage of 4 99V could be obtained when the input voltage was varied from 7V to 15V The heating resistor of the sensor was connected as the load As shown in the Figure 3 22 the circuit was given an input of 15V to produce an output of 4 99V The difference of 02V with the simulated voltage could be the losses in the circuit The input current of the circuit was measured to be 165 mA The current consumption almost the same as the simulated result obtained 27 Figure 3 22 Experimental setup 3 4 4 Heating Circuit for CO Sensor 3 4 4 1 Design The CO sensor requires a high voltage and low voltage to be provided alternately for its heating After applying a high voltage of 5 0 1 V for 60 seconds a low voltage of 1 4 0 1 V has to be provided for 90 seconds A transistor is used in combination with the regulator for switching between the two regulated voltages The transistor used is 2N2222 This transistor is a NPN bipolar junction transistor which can be used for medium and low power application with high switching speeds In the circuit in Figure 3 23 V1 represents the adapter voltage 1 e the input for the circuit The resistors R1 R2 R3 and R4 are used for determining output voltage of regulator The resistor R7 1s the heating resistor The voltage source V2 represents the control voltage o
8. 0 here a and b are the unknown parameters H 5000 V 1 0 V is the matrix for sensor output voltage in millivolt unit x n is the concentration measurement in ppm unit taken from the Graywolf sensor Least square error E 0 Yao x n y n x H 0 x H 0 xix 2xH0 0 H HO For minimizing the least square error E 0 E 0 00 Putting 2H x 2H H 0 0 we get 0 H H H x Solving for 0 we get a 0 3618 and b 472 47 2d Hence the equation for CO2 concentration is y n 0 3618 5000 V n 472 47 Estimated CO2 concentration in ppm unit Then voltage values were put in this equation to see 1f 1t matches with the concentration measurement from Graywolf sensor The Figure 6 10 plots the estimated concentration y n and the concentration measurement x n taken from Graywolf system Graywolf e Estimated 00 O gt CO2 ppm ON O O EN MN 3 roo O No of Readings Figure 6 10 Estimated CO2 concentration and the Graywolf measurement Experiment 2 6 3 1 Conversion formula for the VOC Sensor The signal model for the VOC sensor was taken as y H 0 where H is the observation matrix and 0 is vector parameter of dimension 2X1 0 o here a and b are the unknown parameters H V_ 1 0 V isthe matrix for sensor output voltage millivolts x n is the concentration measurement in ppb unit taken from Graywolf sensor
9. XBP24BZ Figure 5 1 XCTU software showing the configuration of Xbee Modules 5 2 Data Acquisition The base station or coordinator receives the data at regular intervals from the routers or sensor nodes Each sensor node is programmed using Arduino programming for collecting the sensor output values A timer 1s set in Arduino which start counting when the program begins running After each 5 minutes the data 1s collected The data of individual nodes are collected by the coordinator node which 1s connected to the computer The collected values are stored in the computer in text files Python programming is done to store the collected data in files Python x y ver 2 7 3 is used It is an engineering and scientific development software based on python programming language Qt graphical user interfaces and Sypder environment used for analyzing visualizing and computation of data 24 49 CHAPTER 6 CALIBRATION 6 1 Calibration Setup The sensors we have used in our system are inexpensive sensors Its output may not be accurate and may depend on several factors The datasheet of these sensors did not have conversion formulae to convert the output voltage to gas concentration units Hence it was necessary for these sensors to be calibrated For the calibration of the gas sensors it required special chamber for maintaining the gas concentration at fixed levels a source for generating the gas and a reference instrument for measuring the act
10. c Connection diagram 6 The ozone sensor is a six pin sensor The Pins A and B are used to fetch signals and H pins are used for heating the sensor For the measurement of sensor a loop voltage Vc and heater voltage Vu has to be applied to the sensor pins as shown in the connection diagram in Figure 3 3 When the sensor reaches the required temperature output 1s measured across the adjustable load resistor RL The load resistor Rr is connected in series with the sensor The value is of this resistor 1s chosen in such a way to obtain a good range of output voltage We have taken its value as 10kohms For meeting the heating power requirements of the sensor a heating circuit has to be designed The specifications of the sensor are given in Table 3 3 3 2 4 Carbon Monoxide Sensor MQ 7 Carbon monoxide sensor is also a heating semiconductor sensor similar to VOC and ozone sensors although its heating requirements 1s slightly different from them The working principle and composition of the semiconductor type sensor are explained in section 3 2 2 It is highly sensitive to carbon monoxide and has long stable life 10 nn Figure 3 4 a CO sensor b Connection and pin diagram 7 Table 3 4 Sensor Specifications Value 5 0 0 1 V AC DC 5 0 0 1 V AC DC 1 4 X 0 1 V AC DC 60 1 seconds 90 1 seconds Heater resistance Ru 33 5 Q Room Temperature Heater Power Consumption 350mW Standard working conditions Mo
11. 2 WV 6 9 NV 6t S WV 68 7 WV 60 7 WV 6r WV 62 C WV 6 T WV 6t cI Wd 6S TT Wd 60 TT Wd 6T 0T Wd 62 6 Wd 6 8 Wd 67 2 Time of day Figure 6 6 Carbon monoxide sensor output in mV from the IAQ system WV 67 01 WV 65 6 NV 60 6 WV 61 8 NV 62 2 WV 6 9 NV 6t S WV os v WV 60 7 NV 6r WV 62 C WV 6 T NV 6t cI Wd 65 TT Wd 60 TT Wd 6T 0T Wd 62 6 J Wd 6 8 _ a L E Wa 6 2 qdd uone nuo uo Time of day Figure 6 7 VOC concentration in ppb from the Graywolf Sensor WV 67 01 WV 68 6 WV 60 6 WV 61 8 WV 62 2 WV 6 9 WV 6t S WV os v gt NV uid NV 6L o NV Sud WV 6 T NV 6t cI Wd 65 TT Wd 60 TT Wd 6T 0T Wd 62 6 Wd 6 8 Wd 67 2 Figure 6 8 VOC Sensor output in mV from the IAQ System 55 x lt A N A A Ov OV O el AH 11 59 PM 12 49 AM 10 49 AM Time of day Figure 6 9 Temperature C and relative humidity 96 readings from the Graywolf sensor 6 3 Modeling and Estimation In the above experiments the outputs of CO VOC sensors increased linearly as concentration of gas 1s increased For CO2 sensor voltage output decreased linearly as carbon dioxide increased The temperature humidity sensors are already calibrated They showed a deviation in reading due to the heat dissipated within the module It was observed from the experiments conducted that the temperature in sensor node module 1 was higher by 4
12. 24 it is observed that a voltage of 4 97V is obtained when control voltage is LOW 0 to 0 6V and a voltage of around 1 42V is obtained when the control voltage is HIGH As in Figure 3 25 the current intake is observed to be 153 mA when control voltage is LOW and around 45 mA when control voltage is HIGH with the input voltage Vin 15V Figure 3 24 Output voltage vs control voltage V2 Vin 15V 30 1404 14 0x1 1101 1004 ETEA LIE M 0 5 1 07 1 57 2 07 2 5 3 07 1 57 4 07 4 57 3 07 c IJP IN Figure 3 25 Input current vs control voltage V2 Vin 15V Figure 3 26 shows that a regulated voltage of 4 98 V is obtained when input voltage is varied from 7V to 15V when control voltage is kept at OV 5 2v es DEN DPA CI PS O AC A A AA A DOSE REM IA AA A A OA A A PUN DOS A O CT E UR EON SSE c A A AA A A OOO ACA A TA A RA A PO MECA OA RC OA A AS e E PA A A A A IA A A A A A A E A T A 1 nd ccdacdacdecdeadssdeccbech os pida l i BEN y y T IL 4 oe ee ee eee P Li FOER ERNES BSRR RAREN PLbib bii PP PP D PPP iil lil il ilii AA A Lili iii REE EA AAA TUR ECO PERO PORRA ER RA RA PO OO LOS ELI DONO UN A AA RCA AS IC RS e emeret derer d a pos exem engeren dejen ederent pen remet O perennem RS ARI else s 4 4 4 4 pm O AA E O DA AO O AA A O AA AA A AO A om uuum 4 6 or n ss 1 1 L 1 i y EN iiibiiii iiiipiii
13. 3 6 represents the sensor s output voltage The resistors R1 and R2 determine the gain of the amplifier The capacitor Cl acts as the low pass filter V2 79 i Vin 1 Vout 700mVdc M 6 8k C1 100nF o Figure 3 6 Signal conditioning circuit for CO2 sensor 13 3 3 1 Signal Conditioning Circuit for CO2 3 514 Design Gain of the amplifier The positive power supply voltage of 5V and the negative supply voltage of OV is given to the Op amp As MCP6001 can produce rail to rail output an output voltage of range 0 to 5V can be obtained The required gain to amplify the maximum output voltage of the sensor to the saturation voltage of the Op amp is Gain max 5000mV 600mV 8 33 The actual gain for the amplification 1s taken lesser than the maximum gain Hence Gain 7 8 The gain of MCP6001 is given by the equation G 1 RI R2 To obtain the gain of 7 8 we set RI 6 8 k ohms and R2 1 k ohm Cut off frequency of the filter Arduino Uno takes 100us to read an analog input Hence the maximum sampling frequency possible is 10kHz According to Nyquist Sampling rate sampling frequency max gt 2 Signal frequency Le Signal frequency lt Sampling frequency 2 5kHz Hence the cut off frequency of filter should be less than 5 kHz A cut off frequency of approximately 200 Hz can be obtained by using a 100nF capacitor A frequency of this range 14 was selected as the change in carbon dioxide in the air 1s expecte
14. 3 Experiments and Tests The circuit was tested using a DC power supply and Agilent multimeter When the input voltage was varied from 8V to 15V a constant output voltage of 5 94 V was attained The heating resistor of the sensor was connected as the load As shown in the Figure 3 14 the circuit was given an input of 15V to produce an output of 5 94V It 1s a little lesser than the simulated output This could be due to the losses in the circuit The current intake was observed to be 130 mA The current consumption was lesser than the simulated current as the resistance of the heater resistor increased due to the temperature rise The sensor heater resistance was measured using the multimeter It was measured to be 45 ohms when it got heated to the required temperature It was increased from 30 ohms to 45 ohms E Es md Figure 3 14 Experimental setup for heating circuit 21 3 4 2 Heating Circuit for VOC Sensor 3 4 2 1 Design The heating resistor of the sensor requires a voltage of 5 0 2 V and takes a current of approximately 56 mA The resistor R3 in the Figure 3 15 represents the heating resistance of the VOC sensor at room temperature The values for resistors R1 R2 and R4 are chosen using the output equation of the regulator given as Vo 1 25 1 R2 RARI Putting Vo 5V 5 1 25 1 R2 R4 R1 Taking R1 240 ohms R2 R4 720 ohms Approximating the resistance values to available standard resistors R1 240 ohms R2
15. 680 ohms and R4 360hms Vin lin 2 3 lout Vout V1 15Vdc C2 0 1u R3 Bg O Figure 3 15 Heating circuit for VOC sensor 224122 simulations The graphs of input voltage vs output voltage and input current vs output voltage were plotted in Cadence PSpice In the Figure 3 16 it was observed that a constant voltage of 5 01V 22 was obtained when input voltage was varied from 7V to 15V AAA AAA AAA A AA AAA ASAS AAA AA AAA AAA ASAS AS AA AAA AAA SAS AA A PA eed A PAI PA ISA PA RI EA AS AA A O A RA PA SR MAI AA AAA AAA A PARRA A PA AAA A O PR A A EA A AAA beoqse AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA AAA SA A AAA ARAS AAA AA A AAA ARAS AS A AAA ASE AAA AAA AAA A ARA AA AAA A 4 4 AS AAA AAA AAA AAA AAA AAA AAA A AAA AAA A AAA AAA AAA A TS beeecepeeqeoceedecasecsos2scscsdesqeecsccccepocboococcecqesccecbocpoospescocccode os Poococqecdocsee ccc ep cep cc foc ccc gece cc Pec ospoosocococ odeee ee ce gsc ge cds cece peogeosocdocQesqesoe eese focpocncnncanoprrbrccaraogonoconhocoropercosanadacaancnnaegos hecsesposgssccodocaseapaososacodosgoesessescopochocssosooqosesse oespooposcescsodhoasessoossogoodoescsossopooposiesasoaseaposscoehoopooscoecsesadeooscssosqosgoodacoscopeopacsaodooqesqesosossoeloagsasesescepos oossososgosasadsacsosposccssodooaosossessopgoo ee oe o OO E T G o a TEE ee TTT a A ee ee ee ee eee ee ee eee Cee T T T OTOT RT A eee T T SV 89 0 8 5V 5 uv 9 5V 1 UV 18 5V 11
16. HV 11 5V 12 UV 12 5V 13 Pf 13 5Y 14 Uv 14 5V 15 UV 3 Vf IOUTI Figure 3 16 Input voltage vs output voltage From the graph in Figure 3 17 the current consumption was observed to be a constant of 90 1 mA when input voltage was varied from 7V to 15V 23 mA e M n H h T o n S nV P rN V_h H O t OP vP P r D r n v H A E F r _ TD V T n n M B5 Snl 85 mA aa 7 0V 7 51 a ey a w 93 0V 5 51 10 0 18 5Y 11 8Y 11 5V 12 0V 12 5 13 0V 13 5V 14 0V 14 5V 15 0Y 1 01 I8 Figure 3 17 Input current vs input voltage 3 4 2 3 Experiments and Tests The circuit was tested using a dc power supply and Agilent multimeter A constant output voltage of 4 99V could be obtained when the input voltage was varied from 7V to 15V The heating resistor of the sensor was connected as the load As shown in the Figure 3 18 the circuit was given an input of 15V to produce an output of 4 99V The difference of 02V with the simulated voltage could be the losses in the circuit The input current of the circuit was measured to be 63 16mA The current consumption was lesser than the simulated current as the resistance of the heater resistor increases when temperature rises To ensure the increase in resistance the heater resistance of the sensor was measured It was measured to be 79 ohms under operating conditions 24 Figure 3 18 Experimental setup for heating circuit
17. _ Zl ARDUINO 1 36 The microcontroller in Arduino UNO is Atmega328 It is preprogrammed with a bootloader which helps in uploading the programs into the microcontroller memory without the need of an external device programmer Atmega328 belongs to Atmel 8 bit microcontroller family It has advanced RISC architecture Its features include 32KB flash memory with read while write capabilities IKB EEPROM 2KB SRAM 23 general purpose I O lines 32 general purpose working registers three flexible timer counters with compare modes internal and external interrupts serial programmable USART a byte oriented 2 wire serial interface SPI serial port 6 channel 10 bit A D converter programmable watchdog timer with internal oscillator and five software selectable power saving modes Arduino is programmed using the Arduino programming language based on Wiring and the Arduino development environment based on Processing Its features are briefed in the Table 4 1 4 3 Wireless Communication Module 4 3 1 Xbee PRO S2B We have used Xbee module for wireless communication as they are small cost effective radios which enable low power and low bandwidth simple wireless communication Xbee 1s a wireless microcontroller made by Digi International It has 20 pins of which 11 are digital I O pins and 4 are analog pins Xbee PRO series 2 1s used as 1t consumes lesser power and gives better range than Xbee Series 1 It uses a frequency of 2 2 GHz 10 The com
18. common source which produced all of these gases was used A paper was burnt and was kept near the sensors placed in the test container We know that the incomplete combustion of a substance produces of a mixture of carbon monoxide and carbon dioxide gas Burning of paper is an example of incomplete combustion It produced CO CO2 and VOC gases The VOC might 53 have been produced due to the volatile matter of the burning paper The container was kept closed to maintain these gases for a while The data was collected in each 5 minute intervals by keeping the sensors along with gray wolf sensor inside the test container We can see from the Figure 6 5 and 6 7 that the concentration of CO and VOC increased drastically for some time and then decreased CO2 also increased to 1000 ppm Similar pattern of variation was observed for the CO2 concentration also Comparing the sensor output values with the concentration of the gases we observe a linear relation for VOC and CO For CO2 sensor the variation was similar to that found for the Experiment 1 Figure 6 9 plots the temperature and humidity variations from the Graywolf sensor 9 8 6 5 4 3 2 1 cOOOOo00o00 7 39PM4TTTTTTT T 8 39 PM P m E a c w E D qu E Q Q E Q 10 19 PM 11 09 PM 11 59 PM 12 49 AM 10 49 AM Time of day Figure 6 5 Carbon monoxide concentration in ppm from the Graywolf sensor 54 WV 67 01 WV 65 6 NV 60 6 WV 61 8 NV 62
19. from Graywolf system and IAQ system Test 2 nd ZT 6 Wd 27 8 Wd Z Z Wd Zv 9 Ind ZS S nd 20 5 Wd LT Figure 7 8 CO concentration ppm from Graywolf system and IAQ system Test 2 e N O u Graywolf lAQ m e c Q E qu E Q Qs E Q oc ul 10 07 PM 10 57 PM 11 47 PM 10 37 AM Time of day Figure 7 9 Temperature in Celsius from Graywolf system and IAQ system Test 2 N N O O un O Graywolf JAQ Relative Humidity Y Ui 10 07 PM 10 57 PM 11 47 PM 10 37 AM Time of day Figure 7 10 Humidity concentration from Graywolf system and IAQ system Test 2 7 2 Analysis From both the tests we observe that the values obtained from our system displayed good relation to the standard system we used for comparison In the first test results it can be clearly 65 seen that gas sensors in our system responded to the pollutants faster than the Graywolf system However they took longer time to come back to the normal values than the Graywolf system This trend of slow decline was observed for the second test also From the second test results we notice that our system was less sensitive than the standard system for higher concentration of pollutants whereas 1t can be seen from Test 1 that 1t responded similar to Graywolf system when the pollutant concentration was not very high On the whole the performance of the IAQ system was good enough for
20. minutes The data collected was then plotted to study the characteristics of the sensors 6 2 1 Experiment 1 Data was collected for different weeks from our lab at normal conditions Our system was kept close to the Graywolf system and readings were taken at an interval of 5 minutes Except for CO2 humidity and temperature all the other parameters were present in negligible concentration The Figure 6 1 shows the CO2 concentration from Graywolf sensor and Figure 6 2 shows the CO2 sensor output of our system The Figures 6 3 and 6 4 shows the temperature and humidity values collected We can see that the carbon dioxide concentration increased from 9 00 a m and reached 1ts peak at 3 00 p m and then gradually decreased This variation was seen as 10 was a Monday and the presence of people made the CO2 concentration vary During the previous two days Saturday and Sunday the concentration was almost a constant low value m E E c a qu E E lt P Q Q Figure 6 1 Carbon dioxide concentration in ppm from Graywolf Sensor 51 x gt lt NO 00 N 2 8 11 AM 2 8 4 PM 2 8 9 PM 2 9 2 AM 2 9 7 AM 2 9 12 PM 2 9 5 PM 2 9 10 PM 2 10 3 AM 2 10 8 AM 2 10 1PM 2 10 6 PM 2 10 11 PM 2 11 4 AM Date Time Figure 6 2 Carbon dioxide sensor output in mV from IAQ system It is observed by comparing Figures 6 1 and 6 2 that CO2 sensor voltage decreased linearly as the CO2 concentration incre
21. were the connected together by Zigbee network The nodes were developed in such a way that 1t 1s compact in size and wireless connection of sensor nodes enable to collect air quality data from multiple locations simultaneously The collected data was stored in a computer We employed linear least square approach for the calibration of each sensor to derive a conversion formula for converting the sensor readings to engineering units The system was tested with different pollutants and data collected was compared with a professional grade monitoring system for analyzing its performance The results indicated that the data from our system matched quite well with the professional grade monitoring system Copyright 2014 by Sherin Abraham 11 ACKNOWLEDGEMENTS This thesis would not have been possible without my close association with many people I take this opportunity to extend my sincere gratitude and appreciation to all those who made this thesis possible First and foremost I would like to extend my sincere gratitude to Dr Xinrong Li my advisor for his constant support and help throughout my thesis work His continuous encouragement and advice has helped me to improve my ways of learning and thinking styles I would like to thank Dr Yan Wan and Dr Kamesh Namuduri for being my committee members and guiding me in my research I am very thankful to my department for supporting me financially for my studies My heartfelt regards to my friend
22. 4 Temperature in Celsius from Graywolf system and IAQ system Test 1 62 N N O c aa O sraywolf AQ pa Ct c lt 3 15 Z p S o a Figure 7 5 Humidity concentration from Graywolf system and IAQ system Test 1 7 1 2 Test 2 Another test was performed to see how VOC sensors responded when it was exposed to other types of volatile materials For that two to three drops of nail polish remover was poured into a piece of cotton and was placed in the test chamber with its lid closed The nail polish remover used was the one containing 100 acetone The readings by both the systems are shown in Figures 7 6 to 7 10 Graywolf AQ VOC ppb l f 8 27 PM 3 gt E Ed E J E dj T 5 07 PM 5 57 PM 6 47 PM 4 17 PT N N D No c o 10 07 PM 10 57 PM Time of the day Figure 7 6 VOC concentration ppb from Graywolf system and IAQ system Test 2 63 Graywolf NV Ze 0T NV Zb 6 WV ZS 8 WV Z0 8 NV ZT Z NV Zc 9 NV Ze S NV Zv v NV ZS NV Z0 WV ZT Z Time of the day yraywolf WV Ze 0T NV Z 6 WV ZS 8 WV 20 8 NV ZT Z TWV 2 9 JV LE S NV Zi NV LSE NV Z0 NV ZT Z 64 Id 5 01 Wd 0 0I Wd 0 0T 00 O udd zo Wd ZYT 6 Wd 2 8 Wd Ze Z Wd Z 9 Wd ZS S Wd Z0 S Wd ZI v l Wd Zv TT Wd ZS 0T o Figure 7 7 CO2 concentration ppm
23. 5 C and humidity lower by 6 In sensor node module 2 temperature was higher by 6 5 C and humidity lower by 7 5 This can be corrected using a correction factor It was observed that these gas sensors were independent of slight temperature and humidity variations Therefore a linear signal model is assumed with two unknown parameters for all the sensors The estimation is done using the Least Square Approach In this method a signal model is assumed and no probabilistic assumption is made about data Statistical performance can t be assessed as no assumption of data is made But this estimator is widely used because of its ease of implementation 16 56 In this estimation technique we try to minimize the squared difference between the actual signal and the assumed signal 16 Let the actual signal be x n and assumed signal be y n The assumed signal may depend on several parameter Suppose 0 is the unknown parameter it 1s depended on Then least square error is given by E 0 Ynzo x n y n Here N 1s the number of observations taken The least square estimator 1s the value of 0 that minimizes E 0 It will be a value that makes y n closest to x n The estimation was done in MATLAB ver 7 14 for the measurements taken from Experiment 2 6 3 1 Conversion formula for the CO2 Sensor The signal model for the CO2 sensor in vector form was taken as y H 0 where H is the observation matrix and 0 is vector parameter of dimension 2x 1 a
24. 9 0000650 Dur zi Jn x E i t s NP TA BD a r A c s 3 w A e 3 eet Sie i kai J O a i x r IL mc cf ly 5 dt E Zi ae 7 l e gt s bicis SEC 2n X ANN It 4 Figure 4 9 Type I sensor node module The sensors in sensor node type II are ozone CO and temperature sensor The ozone sensor needs a regulated voltage of 5V and 180 mA for the heating purpose The CO sensor requires a constant high voltage of 5V and low voltage of 1 4V and consumes a maximum current of 250 mA Along with the Xbee module maximum current consumption comes around 650 mA Hence a 9V A adapter was chosen for powering this Module It is implemented in a similar way as senor node I The sensor shield and Xbee is mounted on Xbee shield which is placed on top of the Arduino The final implementation of the type II sensor module is as shown Figure 4 10 44 wooo OPO eo y o Dae O99009000RNE o AEF y y y gt E 7 gt Figure 4 10 Type II sensor node module 45 CHAPTER 5 NETWORK ARCHITECTURE AND DATA ACQUISITION 5 1 Network Architecture The network we propose consists of several sensor nodes organized in ZigBee network One of the nodes 1s the ZigBee coordinator and the others are end devices or routers Details of the communication protocol used operation of communication module and how the network 1s set up is discussed in this section 5 1 1 Operation of Communication Module As mentioned before w
25. DEVELOPMENT OF A COST EFFECTIVE WIRELESS SENSOR SYSTEM FOR INDOOR AIR QUALITY MONITORING APPLICATIONS Sherin Abraham B Tech Thesis Prepared for the Degree of MASTER OF SCIENCE UNIVERSITY OF NORTH TEXAS May 2014 APPROVED Xinrong Li Major Professor Yan Wan Committee Member Kamesh Namuduri Committee Member Shengli Fu Chair of the Department of Electrical Engineering Costas Tsatoulis Dean of College of Engineering Mark Wardell Dean of the Toulouse Graduate School Abraham Sherin Development of a Cost Effective Wireless Sensor System for Indoor Air Quality Monitoring Applications Master of Science Electrical Engineering May 2014 69 pp 7 tables 63 figures bibliography 30 titles Poor air quality can greatly affect the public health Research studies indicate that indoor air can be more polluted than the outdoor air An indoor air quality monitoring system will help to create an awareness of the quality of air inside which will eventually help in improving it The objective of this research is to develop a low cost wireless sensor system for indoor air quality monitoring The major cost reduction of the system 1s achieved by using low priced sensors Interface circuits had to be designed to make these sensors more accurate The system 1s capable of measuring carbon dioxide carbon monoxide ozone temperature humidity and volatile organic compounds The prototype sensor node modules were developed The sensor nodes
26. F module to enter states of low power consumption when not in use In command mode the incoming data is interpreted as commands This mode is used to read or change the module parameters 5 1 2 ZigBee Protocol ZigBee specifies a set of high level protocols for wireless networking applications It 1s based on IEEE 802 15 4 MAC PHY as a standard and adds a network layer above it for advanced mesh routing capabilities It is very suitable for home and industrial applications as it designed for low power low data rate and low cost applications ZigBee operates in radio bands 868 MHz 915 MHz or 2 4 GHz Data transmission rates ranges from 20 kbps to 250 kbps It enables good network security by using 128 bit symmetric encryption keys 17 It supports three types of devices coordinator routers and end devices Coordinator selects the PAN ID for the network and it connects routers and end devices to the network Each network is defined with its unique PAN ID Hence a coordinator is in charge of setting up the entire network There can be only one coordinator for a network It should always be powered There can be multiple routers in a network A router has to first join a network After that 1t can allow other devices to join the network and also helps in routing data The router also can never go to sleep The end devices have to join the network for transmitting or receiving data It can neither route data packets nor allow other devices to join the net
27. SA 9 3 2 4 Carbon Monoxide Sensor MQ 7 10 3 2 5 Temperature and Humidity Sensor RTH03 11 3 3 Measunne CIT la oca 2 3 3 1 Signal Conditioning Circuit for CO2 14 o com een uwa S a yas amaga 17 3 441 Heating Circuit for COZ Sensor siria did 18 3442 Hoating Circuit Tor DO led idad 22 345 Hoana Circuit Tor Ozone EOS dd 25 3 4 4 Heating Circuit for CO Sensor cccccccccccccceeeeeeeaaeseeesssseseeeeeeeeeeeeees 28 CHAPTER 4 DESIGN AND DEVELOPMENT OF SENSOR NODE MODULBES 35 4 FAME CD CL A dei usn do e O E Go aaa RUM Cetus 35 A Processime Bor RR 36 4 3 Wireless Communication Module 37 Zl ADEE PRO D2B AAA a mauka O CEU 3T A e A AA 38 aa DESTEMOLE sensor MEA Type da 39 4 5 Design of Sensor Shield Type Il oooooocononcnononnnnnnnnnnnannnnnnnnnnnnnnnnnnnnnncncnnnnnos 4 4 6 Mer PG UN G 0 Sa 43 CHAPTER 5 NETWORK ARCHITECTURE AND DATA ACQUISITION 46 5 1 INSTWOTK ATC HATE CULO a iaa 46 5 1 1 Operation of Communication Module 46 3412 ZeBe LOCO ad 47 SA lo II A Pies au ida is 48 3 2 Data ACQUISITION ner 5e acr DE o en D b eee 49 CHAP TER O CALIBRATION ui ete titration iei aa Ut enata 50 6 1 Calibration Se UA ui toes Me
28. ased It was also observed that the sensor output was not dependent on humidity variations From Figures 6 3 and 6 4 we can see that the temperature of our system is higher and humidity is lower than the actual values This is due to the heat developed by the gas sensors in the module Since the module was designed small and the temperature humidity sensor was put together with more than one gas sensor in a module the reading of the temperature humidity sensor was influenced by the heat developed in the module We confirmed this by hooking up a similar temperature sensor in another module and readings were taken by keeping it far away from the other sensor nodes 22 ice O ul ha N N G mo Ul pa e lt P q O Qu E lt P GrayWolf IAQ Cc ul 2 8 6 AM 2 8 11 AM 2 8 4 PM 2 8 9 PM 2 9 2 AM 2 9 7 AM 2 9 12 PM 2 9 5 PM 2 9 10 PM 2 10 8 AM 2 10 1PM 2 10 6 PM 2 10 11 PM 2 11 4 AM 2 10 3 AM Date Time Figure 6 3 Temperature values in Celsius from Graywolf and IAQ system AQ Realtive Humidity GrayWolf 2 8 6 AM 2 8 11 AM 2 8 4 PM 2 8 9 PM 2 9 2 AM 2 9 7 AM 2 9 12 PM 2 9 5 PM 2 9 10 PM 2 10 8 AM 2 10 1PM 2 10 6 PM 2 10 11 PM 2 11 4 AM 2 10 3 AM Date Time Figure 6 4 Relative humidity in percentage from Graywolf and IAQ system 6 2 2 Experiment 2 For the calibration VOC CO and CO2 sensors respective gases had to be introduced A
29. cg pilirliiiibiiii iiii ei ii Perea pibibliiiibiiiilg AA EE ARAN A A AA A A A A A A A A A A A ee 1 Wo NUM ICA RAROS ROCA ERA BECA MORO CRA RECO OA MORA CRC ACA ROS OIC AO A ee peepee beeper pur qu qud qM MARIA rem erp ee o A ppp 4 4 o a a ol o pe 4 AA A A o der ur o ol ecb dos ol o A uber gen Eds o a o A AA P barro qn do q oq q RENTA AAA AAA AAA Ponds thins dae Seals AA AAA PRA AAA AAA PAR RN sade sins dea TO APA PAPA AAA EA A 4 29 E E A A ee A A A A A A O A O A A die A A A N A A O E A A A A E wa IA AA AE AA OA O A A A MA SAO E rd Pr LM MAA AAA A O A A A PR A A A A A AA NNNM O A 4 0V 7 0v 7 5VW 2 0v 3 5V s 03 3 3v 19 0v 10 51 11 0v 11 5Y 11 0v 12 54 13 9v 13 51 114 0v 14 5v 15 9 y V V0CT yv vi 3l Figure 3 26 Input voltage Vin vs output voltage Vout V2 0V It is observed that an output voltage of 1 42 V could be obtained when the input voltage is varied from 7V to 15V keeping the control voltage at 5V a qv mye te J PT TP n U l t as i i 3 i i j i 3 3 il 7 07 7 EV H 0v Boy 5 07 B cy 10 51 10 5 11 01 11 5 13 0 12 0 13 0 11 0 14 07 1a 15 0 3 VIVDUT Figure 3 27 Input voltage Vin vs output voltage Vout V2 5V 3 4 4 3 Experiments Two power supplies were provided one for the control voltage and the other for the input voltage A constant output voltage of 4 92V was obtained when the input voltage was varied from 7V to 15V at control voltage set as 0 42 V as shown in the Figure 3 28 32
30. circuits are explained in Chapter 3 The parts of sensor node module its selection design of sensor shields and module implementation are discussed in the 4 chapter In 5 chapter the network architecture communication protocol building of the network and how the data 1s collected are detailed The sensors did not have any formula for converting their output to gas concentration units In addition these sensors may not be very precise Hence they had to be calibrated The 6 chapter deals with calibration estimation and derivation of conversion formula Then the system is tested The experiments done with the system the results obtained and observations are discussed in Chapter 7 Finally the summary and future work is given in the Chapter 8 CHAPTER 2 DESCRIPTION OF THE SYSTEM INDOOR AIR QUALITY MONITORING SYSTEM The main components of the system are sensor nodes base station and server The sensor nodes collect the indoor air quality IAQ information from different locations inside the building and this data 1s sent to the base station The base station forwards it to a server Then it can be made available in the internet which can be accessed by web clients Firstly a sensor node has to be designed considering several factors like cost size and power consumption The parameters that can be measured by the system are ozone carbon dioxide carbon monoxide temperature and humidity The cost reduction 1s achieved by using inexpensiv
31. d crc m AUTHOR SA TITLE Sheet1 Figure 4 5 Circuit diagram of sensor shield type 1 40 Figure 4 6 PCB layout of sensor shield type I 45 Design of Sensor Shield Type II This sensor shield comprises of carbon monoxide ozone sensor and temperature humidity sensor The shield size was same as that of the shield I and the headers were used to mount the shield easily on the Arduino The output of the sensors was connected to the corresponding header pins to make it easy to use and handy The circuit diagram of the shield is given in Figure 4 7 The main components of the circuit diagram are sensors regulators transistor and connectors One 6 pin connector and one 8 pin connector is used The voltage regulator U2 provides 5V regulated voltage The regulated 5V is used for heating ozone sensor and for the measuring circuits of all the sensors The CO sensor requires a constant high voltage of 5V and low voltage of 1 4V to be given alternatively This alternating voltage is provided by regulator U1 in combination with the transistor 2N2222 The design details of the heating and conditioning circuits had been discussed in the previous chapter 41 The power 1s obtained through the Vin pin and Gnd pins of Arduino board through the jumper JP1 The control voltage for switching the transistor on and off is given through the digital pin 2 through the connector JP3 The output of temperature sensor 1s connected to the digital pin 4 by the co
32. d to be slow A capacitor of 100nF is used as a low pass filter to obtain a cut off frequency of 210 Hz Hence C1 100 nF 3 3 1 2 Simulation DC Analysis iv 5 mv 10m V 1541 20m Y 25 baV Atta AStaV 4007 45 nV tim 55 mV f fmV 5 mV 70 mV c VIYUUT Figure 3 7 Input voltage vs output voltage of signal conditioning circuit For the DC analysis DC voltage input was varied from 0mV to 700 mV and the output voltage of the circuit was observed An amplified output of range 4700 mV to 800 mV was obtained for maximum 600mV and minimum voltage 100 mV output of the sensor 15 3 3 1 3 AC Analysis Frequency Analysis E c BRAY Foun fV Pied Figure 3 8 Frequency response of the filter The frequency response was obtained by giving an input signal of magnitude 600 mV with frequency varying from 10Hz to 30kHz The Gain of Op amp in Decibels is G 20 log Vo Vin Since the input signal magnitude given is Vin 600mV the output is Vo 4700mV The the gain is G 20 log 4700 600 17 87 Db From the Figure 3 8 it 1s observed that the same gain is obtained The cut off frequency of filter is found to be 210 Hz Hence the filter passes signals with frequency lesser than 210 Hz and attenuates signals greater than 210 Hz 3 3 1 4 Experiments and Tests The tests were conducted using A gilent multimeter and a power source DC voltage was 16 applied to the conditioning circuit using a power source The amplifi
33. dia http en wikipedia org wiki ZigBee 18 Final Report Embedded Systems for Environment Sensing http mesl ucsd edu gupta cse237b f09 ProjectReports EnvironmentalSensing pdf 68 19 Ying Han Neng Zhu Nan Lu Jing Chen Yan Ding The Sources and Health Impacts of Indoor Air Pollution Bioinformatics and Biomedical Engineering 1CBBE 2010 4th International Conference on vol no pp 1 4 18 20 June 2010 do1 10 1109 ICBBE 2010 5515150 20 United States Environment Protection Agency Indoor Air Quality http www epa gov 1aq 21 Occupational Health and Safety Administration Indoor Air Quality in Commercial and Institutional Buildings https www osha gov Publications 3430indoor air quality sm pdf 22 PPM Technology Wireless IAQ Profile Monitor http www ppm technology com 23 Bhattacharya S Sridevi S Pitchiah R Indoor air quality monitoring using wireless sensor network Sensing Technology ICST 2012 Sixth International Conference on vol no pp 422 427 18 21 Dec 2012 do1 10 1109 ICSensT 2012 6461713 24 Python Tutorial http docs python org 2 tutorial 25 Jelicic V Magno M Paci G Brunelli D Benini L Design characterization and management of a wireless sensor network for smart gas monitoring Advances in Sensors and Interfaces IWASI 2011 4th IEEE International Workshop on vol no pp 115 120 28 29 June 2011 doi 10 1109 IWASI 2011 6004699
34. dings Figure 6 12 Estimated CO concentration and the Graywolf measurement Experiment 2 The conversion formula for CO CO2 and VOC sensor was modeled using the data collected from Experiment 2 The equations modeled here were used in the tests carried out in the next chapter for calculating the gas concentration for our system 60 CHAPTER 7 RESULTS AND ANALYSIS 7 1 Testing Experiments were performed with different pollutants to analyze the performance of our system and the accuracy of the equation we modeled The sources which produced these pollutants were burning material for the first test and acetone based nail polish remover for the second test These are common pollutants that can cause poor indoor air quality 7 1 1 Test For the first test a paper was burnt for a short duration and flames were put off immediately Then it was put in our test chamber containing the Graywolf and IAQ system and the chamber lid was closed The results produced were as shown in Figures 7 1 to 7 5 Gray Wolf Time of the day Figure 7 1 VOC concentration ppb from Graywolf system and IAQ system Test 1 61 gt e E Figure 7 2 CO2 concentration ppm from Graywolf system and IAQ system Test 1 gt oO E Figure 7 3 CO concentration ppm from Graywolf system and IAQ system Test 1 m gt qv E Mm c WM N C a wo 9 o m3e 19dulo l wn Figure 7
35. e have used Xbee as the communication module Its hardware details were explained in the previous chapter Here we will see how it operates Xbee module interfaces to the host device through a logic level asynchronous serial port The data enters the module UART through its D3 pin The module has a buffer to store this data Each data byte consists of a start bit 8 data bits and a stop bit The start bit has low voltage level and stop bit has high voltage level It has two serial interface protocols One is Transparent Serial Interface AT and the other is packet based Application Programming Interface API In AT mode the data is transmitted to the intended receiving module without any modification For controlling the radio settings AT commands can be used In API mode the data has a packet structure It allows addressing parameter setting and packet delivery feedback and may also include remote sensing and control of analog and digital pins It has five modes of operation These are Idle sleep transmit receive and command mode 10 Xbee module is in idle mode when it 1s not receiving or transmitting data It goes to 46 transmit mode when the data in the serial buffer 1s ready to be packetized When the data 1s received by the Xbee it enters into receive mode When the modules are not in use it can go to sleep mode Only the end devices can be in this mode In this mode it will be in a low power consumption state Sleep modes allow the R
36. e sensors Hence these sensors had to be conditioned and calibrated The Arduino Uno is used as the processing unit and Xbee module is communication unit for the sensor node The sensor nodes can be placed at several locations for the collection of IAQ data simultaneously from multiple locations The nodes are connected together by a Zigbee network The coordinator or base station is an Arduino board with Xbee module The coordinator is connected to a computer using a USB cable to store the IAQ data in the computer The router node can help in routing the data and coordinator is in charge of the whole network These details are seen in detail in Chapter 5 The data can then be put in the Web server The development of the Web portal is not covered in this thesis The block diagram of the system is given in Figure 2 1 IAQ data Figure 2 1 Block diagram of the indoor air quality monitoring system CHAPTER 3 DESIGN OF INTERFACE CIRCUITS FOR SENSORS 3 1 Introduction The sensors we have used in our system are carbon dioxide carbon monoxide ozone volatile organic compounds VOC and temperature humidity sensors The gas sensors belong to the category of chemical and semiconductor type sensors These sensors require heating and signal conditioning circuits for proper functioning The design simulation and testing of the heating and conditioning circuits for each sensor is detailed in this chapter The design and simulations of the circuits was pe
37. ed Then Vo 1 25 1 R2 R1 3 4 1 Heating Circuit for CO2 Sensor 3 4 1 1 Design The heating circuit of the sensor requires a heating voltage of 6 0 1 V and current of 200mA as given in Table 3 1 The heating circuit is shown in Figure 3 11 R3 is the sensor s heating resistance at room temperature The output of the regulator is Vo 1 25 1 R2 R1 The value of the resistors is obtained by equating the output voltage equation to 6V 6V 1 25 1 R2 R1 R2 RI 3 8 18 Taking R1 180 ohms R2 684 ohms R2 is approximated to a standard resistance value 680 ohms Therefore R2 680 and R1 180 This gives Vo 5 972 V U1 LM317K IN OUT lt R3 30 Figure 3 11 Heating circuit for CO2 sensor 34 1 2 Simulations From the simulation graph shown in the figure 3 12 1t was observed that a constant output voltage of 6V could be achieved for the input voltages between 8 V to 15V Figure 3 13 shows that the heating circuit takes a current of 207 mA 19 1 1 1 r i sad r L andado il ee lol eee 1 1 1 r r 1 1 D D D t k D A s ss qas qes Bla A A A tmm nam e ee le Kk mx O A E lt rr Bene Cee queue qo A A A qasasqa et ee mpe me ea ajea mr A qam drm mmm HR mmn mr 1 eee ees
38. ed voltage observed from the multimeter was found to match with the simulated results The Figure 3 9 shows that the circuit produced an output of 4 45V when an input voltage of 600 mV was given Figure 3 9 Experimental Setup for Conditioning Circuit 3 4 Heating Circuits All the gas sensors have to be heated to a particular temperature for its working Each of them requires specific heating voltage requirements Carbon dioxide sensor required 6V regulated heating voltage while ozone and VOC sensor required 5V Carbon monoxide sensor required 2 voltage levels which has to be switched alternately after certain time periods LM317T was selected as the voltage regulator for obtaining constant voltage levels LM317T is a three terminal positive adjustable regulator which can give a regulated output between 1 2V to 37V It is capable of providing an output current of more than 1 5 A 3 17 Output 1 1 Adj 2 Output 3 Input Figure 3 10 Pins and connection diagram 3 The pins of the regulator and the circuit for general applications are given in Figure 3 10 The resistors R1 and R2 determine the voltage output of the regulator The capacitor Co 1s added to improve the transient response and Ci 1s used when the regulator 1s located far from the power supply filter The voltage output of the regulator is given by the equation Vo 1 25 1 R2 R1 lady R2 3 Since Iadj is lesser than 100 uA the term ladj R2 can be neglect
39. ene meses 50 6 2 Experiments 51 OE EXP la 51 O22 0 A dto mbi TDi bant P ola 53 6 3 Modele and ESTIMAN ceret REL E Ert rhet I Mp Heu ied 56 6 3 1 Conversion formula for the VOC Sensor 58 632 Conversion formula Tor the C O Sensor vcd 59 CHAPTER 7 RESULTES AND ANALY SES or USERS OU P ERI NE et 61 7 1 PP O 61 VN GELT A TE 61 NOME US ORT RECEN II A ana RUNE 63 o O O ESR 65 CHAPTERS SUMMARY AND FUTURE WORK cra 67 BIBLIOG RAP A a aan and O aa O 68 CHAPTER 1 INTRODUCTION 1 1 Motivation and Background Scientific evidence indicates that indoor air can be more seriously polluted than the outdoor air Indoor air pollution is caused by indoor as well as outdoor pollutants The industrial emissions and traffic exhaust are some of the sources of outdoor pollutants which can enter inside and get trapped if the ventilation of the building is inadequate The main sources of indoor pollutants are cooking smoking cleaning construction materials central heating and cooling systems and humidification devices biological pollutants etc 19 26 Some of the major pollutants are CO2 CO VOCs ozone radon dust and so on The US Environmental Protection Agency and its Science Advisory Board lists poor air quality as the top five health concerns An average person spends 90 percent of their time indoors according to the research studies People exposed to poor indoor air quality environments may get sick with symptoms s
40. f transistor and R5 represents the base resistance 28 When a high control voltage 5 V 1s applied to the base of transistor 1t conducts and the regulator voltage output depends on resistor R1 and R4 Hence resistors R1 and R4 are chosen to obtain a voltage of 1 4 V Putting Vo 1 4V Voltage equation is 1 4 1 25 1 R4 R1 Therefore R1 240 ohms R4 28 8 ohms Approximating R4 to standard resistor value R4 30 ohms Vo 1 406 V U1 LM317K Vin lin 2 Vout IN E 15Vdc l C2 R4 R7 0 1u 30 3 V2 R5 I Q 2N2222 5Vdc S R6 2k O Figure 3 23 Heating circuit for CO sensor When a low voltage 0V to 0 7V 1s given to the transistor base it does not conduct and thus the R1 R2 and R3 controls the regulator output voltage The regulator output voltage is Vo 1 25 1 R2 R3 R1 To obtain 5V 5 1 25 14 R2 R3 R1 Since R1 240 R3 30 R2 1s approximated to 680 ohms which gives an output of 4 9 V 3 4 4 2 Simulations simulations were done by keeping input voltage constant varying the control voltage and by keeping control voltage constant varying the input voltage In Figure 3 4 2 and Figure 3 4 3 29 the voltage output and current intake is plotted for control voltage ranging from 0 to 5V keeping input voltage constant whereas in Figure 3 24 and Figure 3 25 the output voltage and input current 1s plotted for input voltage of range 7V to 15V keeping control voltage constant From the Figure 3
41. low cost indoor air quality monitoring system which 1s compact in size and capable of efficiently collecting air quality parameters from different locations at a time Then this data can be made available in the Internet so that the sensor node data can be accessed by any location in the world 1 3 Contribution to the Research This thesis involved the development of a low cost reliable monitoring system to monitor the indoor air quality parameters The major cost reduction of the system 1s achieved by using low cost sensors First part was to design interface circuits to make it more accurate Then prototype sensor node modules were developed Six air quality parameters can be measured by the system developed Then linear least square approach was employed for the calibration of each of these sensors to derive a conversion formula for converting the sensor readings to engineering units A wireless sensor network was developed to acquire data from the individual sensor nodes and store the data to a PC Finally the system was tested with different pollutants to analyze its performance 1 4 Organization of the Thesis The whole idea of the indoor air quality monitoring system is explained in Chapter 2 First part in building the system is the design of sensor node modules The sensors and their interface circuits form some of the major components of the sensor node The details of each sensor its working design and simulation of conditioning
42. monitoring the indoor air quality parameters as the trend in variations of parameters are good enough for our application Considering the cost of the system and 1ts application 1t showed good performance 66 CHAPTER 8 SUMMARY AND FUTURE WORK A reliable low cost IAQ monitoring system which can measure 6 air quality parameters was developed The low cost sensors used in this system has been made precise and reliable by conditioning and calibrating it The reduced cost of the system compared to the other available system may encourage more people to use this system which will ultimately help in improving the indoor quality of air The sensor units were connected together wirelessly This enables to take measurements from multiple locations and also give access to remote locations More devices like video camera light sensors can be added to the sensor node This will help in the better analysis of the sources causing the pollution More number of sensor units can be made thus making it a full fledged system to collect data from many rooms in a building or house Collecting the data efficiently can be another area of future work Efficient data collection can be done by developing a better communication protocol 67 BIBLIOGRAPHY 1 Carbon Di Oxide Sensor MG 81 1 datasheet http www olimex cl pdf CO2b pdf 2 Operational Amplifier MCP6001 datasheet http ww 1 microchip com downloads en DeviceDoc 21733h pdf 3 Three Terminal Posi
43. munication protocol used is Zigbee The details on Zigbee protocol will be covered in the next chapter The Figure 4 4 shows the Xbee PRO S2B module More features of Xbee are listed in the Table 4 2 37 Table 4 2 Features of Xbee PRO S2B Operating Voltage 2 6V 3 4 V DC Operating Current Transmission 205mA up to 220 mA 4 3 2 Xbee Shield An Xbee shield is used to connect Xbee to the Arduino board The Shield makes Xbee convenient to use as it can be directly plugged into the Arduino without the need of any other connection It makes the module compact and easy to use The Xbee shield provides regulated voltage of 3 3V for the operation of Xbee The Xbee shield has two jumpers The serial communication between Xbee and computer via the USB cable is enabled by putting the jumper in the USB position For the Xbee to communicate to the Arduino the jumper has to be put in Xbee position The shield covers 8 digital pins and 6 analog pins of the Arduino The female pin headers on the shield help to use all the pins except the digital pins 0 and 1 which is used by Xbee The Xbee shield we have used is shown in Figure 4 3 Figure 4 3 Xbee shield Figure 4 4 Xbee PRO S2B 38 44 Design of Sensor Shield Type I This shield is incorporated by carbon dioxide sensor VOC sensor and temperature humidity sensor along with their heating and measurement circuits Temperature humidity sensor is placed away from the gas sensors in the sen
44. nation Address High J 4075AC8A DL Destination Address Low 407AAC8A i MCV Made Identifier Getting modem type OK Modem s firmware not updated Setting AT parameters OK Write Parameters Complete COM5 9600 8 N 1 FLOW NONE Modem Parameter Profile Remote Configuration Versions PC Settings Range Test Terminal Modem Configuration Modem Parameter and Firmware Parameter View m Profile Read write Wie Restore Clear Screen Save Always Update Firmware Show Defaults Load Modem XBEE PRO Function Set Version XBP24BZ7 gt ZIGBEE COORDINATOR AT Y 2047 1 43 Networking BM 3FFFJID PAN ID Bl 7FFF SC Scan Channels o B 3 SD Scan Duration Y 0 Z5 ZigBee Stack Profile Y FF NJ Node Join Time B 3FFF OP Operating PAN ID J 94E6 OI Operating 16 bit PAN ID Bl 17 CH Operating Channel 0 Bg A NC Number of Remaining Children Addressing Bl 134200 SH Serial Number High Y 40744C84 SL Serial Number Low J 0 MY 16 bit Network Address j B 134200 DH Destination Address High Y 40744085 DL Destination Address Low B NI Node Identifier B 1E NH Maximum Hops ow Bl 0 BH Broadcast Radius i B PETAR Md amta Nna Renta Rraadeact Timo Getting modem type OK Madem s firmware not updated Setting AT parameters OK Write Parameters Complete Wersions Download new versions COM6 9600 8 N 1 FLOW NONE
45. nnector JP3 and output of the other sensors are connected to analog pin 1 and analog pin 2 via connector JP2 The PCB design of this sensor shield is given in Figure 4 8 JE EE z Oo wi cL e qi E AUTHOR SA TITLE sheet Dates 2 11 2014 4 54 34 PM Figure 4 7 Circuit diagram of sensor shield type II 42 Figure 4 8 PCB layout of sensor shield type II 4 6 Implementation After the development of the sensor shield boards the parts are assembled together As mentioned before two types of sensor nodes were made Each node had different power requirements which had to be considered for selecting the adapter First senor node contains CO2 VOC and temperature sensor The carbon dioxide sensor requires 6 V of constant voltage and a current of 200 mA whereas VOC needs 5V and 56 mA The power taken by temperature Sensor was negligible The Xbee PRO module draws a current of maximum 220 mA for transmission and 62 mA for reception It requires a supply voltage of 2 7 to 3 6 V Hence the total current taken by the sensors and the Xbee module comes around 43 476 mA The voltage requirements are below 9V The recommended range for powering Arduino is 7 to 12 volts Hence a 9V 1 A adapter was chosen for this sensor node For the implementation of the module the Xbee shield and sensor shield is placed on the Xbee shield This Xbee shield is mounted on top of the Arduino board as shown in the Figure 4 9 3 O 0000900 21
46. r OP Db M a Dd oL Rr 10k Q Temperature 20 2 Humidity 65 5 20 2000 ppm CO Conditioning Period More than 48 hours 2k 2 20k Q in 100 ppm of CO The connection and pin diagram is as shown in Figure 3 4 For standard working condition the circuit voltage Vc is 5 0 1 V For heating the sensor a high and low voltage has to provided alternatively After applying a high voltage of 5 0 1 V for 60 seconds a low voltage of 1 4 0 1 V has to be provided for 90 seconds The output signal measurements is made across resistor Rr after every heating cycle 1 e 2 5 minutes from high voltage to low voltage The value of Rr for standard working condition is 10kohms as per the datasheet 7 3 2 5 Temperature and Humidity Sensor R TH03 RTHO3 1s a digital sensor It is very compact with low power consumption and long term 11 stability For collecting the data from the sensor the microcontroller has to send a start signal to the sensor The sensor then changes its status from stand by to running and sends a 40 bit data indicating the temperature and relative humidity After that the sensor changes it status to standby mode and remains in this mode till it gets another start signal from the microcontroller S Figure 3 5 a RTHO3 b Connection diagram 8 Table 3 5 Specifications Parameter Power Supply Current Supply Sensing Element Operating Range Humidity 0 100 RH Temperature 40 80C Humidity 2 RH Tempera
47. r according to their function and firmware was updated as the latest version The serial interface protocol selected is Transparent Serial Interface The network PAN ID has to be set the same for all modules in the network and the destination address of each module is given in such a way to make the routers and coordinator talk to each other A screen shot of two instances of XCTU software 1s shown in Figure 5 1 It shows one Xbee configured as router and the other one configured as coordinator 48 Modem Parameter Profile Remote Configuration Versions PC Settings Range Test Terminal Modem Configuration Modern Jelka and Firmware Parameter View Profile Read write Restore Clear Screen Save Download new Show Defaults Versions Always Update Firmware Load versions Modem XBEE PRO Function Set Wersion XBP248Z7 ZIGBEE ROUTER AT Y 2247 d E 3 Networking wow J 3FFF ID PAN ID lo IM 7FFF SC Scan Channels lo i 3 SD Scan Duration B 0 ZS ZigBee Stack Profile B FF NJ Node Join Time o I 0 Nw Network Watchdog Timeout B 0 JV Channel Verification io J 0 JN Join Notification 8 3FFF OP Operating PAN ID ld 84E6 DI Operating 16 bit PAN ID Bl 17 CH Operating Channel li C NC Number of Remaining Children 1 3 Addressing e J 135200 SH Serial Number High lg 40744C85 SL Serial Number Low li 6056 MY 16 bit Network Address Bl 134200 DH Desti
48. ram and connections of the sensor 4 The VOC sensor has four pins as shown in the Figure 3 2 Pin and Pin 4 are the heater pins and Pin 3 corresponds to sensor s positive electrode and Pin 2 corresponds to its negative electrode As shown in the connection diagram the heater pins has to be provided a voltage of Vu A circuit voltage of Vc has to be applied to measure the output voltage across the adjustable resistor Rr Table 3 2 Specifications of VOC sensor Sensor resistance Rs normal conditions Since the output of sensor is in the range of OV to 5 V special amplification circuits are not required The load resistance Rr was selected as 3 3Kohms as it gave a good range of output voltage Separate heating circuit 1s designed for the betterment of the sensor performance 3 2 3 Ozone Sensor MQI31 MQ131 gas sensor is a heating semiconductor type sensor The sensitive material in this sensor 1s tin oxide This sensor s composition and working principle is the same as explained for VOC sensor It is highly sensitive to ozone It 1s also sensitive to gases like chlorine and nitrogen dioxide Long life low cost wide range of sensitivity of ozone is some features of this sensor 6 Table 3 3 Sensor specifications 10 1000 ppb Conditioning Period More than 48 hours 50k Q 500k Q in 100 ppb of Ozone P Vc 5 0 0 1 V Standard test circuit conditions Va 5 0 0 1V Figure 3 3 a Ozone sensor b Pin diagram 6
49. rformed using the software Cadence PSpice ver 16 6 Cadence PSpice is industry proven advanced circuit simulation software for mixed or analog signal circuits It is capable of simulating designs from power supplies to high frequency systems to simpler IC designs After doing the simulations the circuits were tested by setting them on the bread board Tests were conducted using a DC power supply and Agilent multimeter Before going to the circuit design and testing the working principle and characteristics of each sensor are explained 3 2 Sensor Details 3 2 1 CO Sensor MG811 MG811 sensor is a chemical sensor The range of carbon dioxide it can detect is 350 10000 ppm It works using the solid electrolyte cell principle When the sensor 1s exposed to carbon dioxide gas chemical reactions occur in the cell producing an electromotive force The surface temperature of the sensor needs to be high enough for these reactions to take place Hence a separate heating circuit is used to heat the sensor to the required temperature 1 The pins of the sensor along with its connection diagram are shown in Figure 3 1 The H pins correspond to the pins of the heating coil The output is obtained from A and B The specifications of the sensor are given in the Table 3 1 Table 3 1 Specifications of the CO2 sensor Heating Voltage 6 0 1 V AC or DC Operating Temperature storage Temperature 20 to 70 C Figure 3 1 a CO2 Sensor b Pin
50. s and connection of the CO2 sensor 1 The Arduino has a 6 channel 10 bit inbuilt ADC Hence input voltages from OV 5V correspond to 0 1023 integer values So the resolution is 4 9 mV per unit integer value 9 As the output voltage of the sensor 1s very low 100mV 600mV it needs to be amplified in order to improve the accuracy of measurements It also requires an external heating supply as its power requirements cannot be satisfied by the microcontroller Therefore it becomes essential to develop a signal conditioning and heating circuit for this sensor 3 2 2 VOC Sensor TGS 2602 TGS 2602 1s a heating semiconductor type sensor It consists of a sensing layer composed of metal oxide material like tin dioxide or zinc dioxide This sensing layer is formed on the alumina substrate of the sensing chip along with an integrated heater The heater requires a warm up time as the semiconducting oxides are sensitive to vapor and other chemicals 5 28 The conductivity of sensor increases when it is exposed to detectable gases The change in conductivity produces an output signal corresponding to the gas concentration 4 TGS 2602 is highly sensitive to low concentrations of gases like ammonia hydrogen sulfide and toluene Its detection range 1s 1 30 ppm Low power consumption long life simple circuit small size and high sensitivity to odorous gases are some of the advantages of this sensor Figure 3 2 a VOC sensor b Pin diag
51. s at University of North Texas for their presence and support have created a better learning environment My special words of thanks goes to my friends Shilpa Jadhav Riya Patil and Vardhman Sheth for they have always been around helping me in various ways I want to thank my lab mate Ferdoush Sheikh for his ideas and observations My parents and sister have always been my greatest strength I would not have reached this point without their infallible love and support I will remember with gratitude the support and help provided by my uncle Paul Sebastian and aunt Nitty Pullikan Above all I am thankful to God Almighty for bestowing with all these goodness and good people around me I also thank God for giving me the strength to tide through the difficult times and overcome the hurdles in my path 111 TABLE OF CONTENTS Page ALCENOWLEDGEMENTS sore uy u luna ae alone lea bo detallo Llei bond oe u Dieta llosa u kas ii CHAPTER T INTRODUC TION riada l 1 1 M otvaton and Back Stout l 1 7 Objectives OF INE Tee Care uuu u luahan ss s 2 1 3 Conttibutlom to he INCSCOECH ocio es Eua ER TERR a Toara 2 LA Orsanizadlonmop He Besi ece 3 CHAPTER 2 DESCRIPTION OF THE SYSTEM INDOOR AIR QUALITY MONITORING SA AA PI Ro E E Ar ee e ET 4 CHAPTER 3 DESIGN OF INTERFACE CIRCUITS FOR SENSORS eese 6 3 1 AA A A A 6 3 2 Sensor DD C xc 6 5 Li cO Sensor MGS Lh ei 6 322 VOC Sensor UGS 2602 nica 8 2 2 9 Ozone Senso MOL
52. sor shield so that its reading doesn t get affected due to the heat of the gas sensors We have used a board of size 6x4cm so as to utilize the space efficiently A 6 pin connector and 8 pin connector were used so that the Sensor Shield can be mounted on top of the Arduino board containing the Xbee shield The circuit diagram and PCB layout of the shield was designed using the Eagle PCB Design Software 12 The VOC and carbon dioxide required regulated voltages of 5V and 6V respectively for their heating It is provided by voltage regulators U2 and U1 as shown in the circuit diagram in Figure 4 5 The output signal of carbon dioxide sensor 1s conditioned using the operational amplifier MCP6001 The measuring circuits of all the sensors require 5V It 1s taken from the voltage regulator U2 The power supply and ground connections are taken from the Arduino using a jumper JP1 The output pin of CO2 and VOC sensor is connected to the analog pin AO and Al through the 6 pin connector JP2 and the digital output of temperature humidity sensor 1s connected to the digital pin 2 of Arduino via JP3 connector The shield can be directly plugged into the Arduino using the connectors JP2 and JP3 After designing the circuit diagram its PCB layout was developed It is shown in Figure 4 6 39 qe air AD WIRES 31F SINK ay L I e 0n cn oa E E ZE ne cL E di DUT IN uc PUA S04 SAS_SENSOR R1 33k TEHP HUITDITTEZEMSUR ames X
53. t the sensors in two separate sensor shields so as to make the sensor node compact and handy Hence two types of sensor shields were designed which had different sensors The temperature humidity Sensor was placed in both the shields to observe 1f the output of gas sensors depended on the humidity and temperature variations We will look into the details of each part their selection design and the final implementation of the sensor node in the following sections 35 4 2 Processing Unit The core of our platform 1s selected as Arduino UNO a single board microcontroller The open source hardware and software low cost easy to use programming and programming environment make 1t popular among the other microcontroller platforms Arduino UNO 1s the latest version of basic Arduino USB boards The board contains a 16MHz ceramic resonator a USB connection a power jack an ICSP header and a reset button It also has 14 Digital I O pins of which 6 is capable of providing PWM output and 6 analog input pins The serial communication is available on digital pins 0 RX and 1 TX The power pins are Vin 5V 3V3 Gnd and IOREF Arduino can be powered through USB or the power jack using an AC DC adapter or battery If it is powered by both the board automatically selects one of 1t 9 Table 4 1 Specifications Operating Voltage 5V DC 6 20V Maximum limits 7 12 V Recommended Memory ATmega328 Hon o eee esi n ws i DIGITAL PWM amp TX
54. tive Adjustable regulator LM317T datasheet http www fairchildsem1 com ds LM LM317 pdf 4 Volatile Organic Compounds Sensor TGS 2602 datasheet http www figarosensor com products 2602pdt pdf 5 Sukwon Choi Nakyoung Kim Hojung Cha and Rhan Ha Micro Sensor Node for Air Pollutant Monitoring Hardware and Software Issues in Sensors No 9 2009 6 Ozone Sensor MQ131 datasheet http www winsensor com Admin uploadfile 201209 201291611559957 pdf 7 Carbon Monoxide Sensor MQ 7 datasheet https www sparkfun com datasheets Sensors Biometric MQ 7 pdf 8 Temperature and Humidity Sensor RTHO3 datasheet http dlnmh91p6v2uc cloudfront net datasheets Sensors Weather RHT03 pdf 9 Arduino http arduino cc 10 XBEE PRO ZB User Manual http ftpl digi com support documentation 90000976 K pdf 11 Xbee Shield http arduino cc en Main ArduinoXbeeShield UwxXwfldWzE 12 EAGLE PCB Design Software http www2 ee ic ac uk t clarke eagle The 20EAGLE 20Guide pdf 13 XCTU http ftpl digi com support documentation 90001003 A pdf 14 IHS GlobalSpec Laboratory and Calibration Gases Information http www globalspec com learnmore materials chemicals adhesives industrial specialty gases laboratory calibration gases 15 Graywolf Sensing Solution http www wolfsense com 16 Steven M Kay Fundamentals of Statistical Signal Processing Vol 1 Estimation theory 1993 17 Wikipedia The Free Encyclope
55. ture 0 5C Humidity 0 1 RH Temperature 0 1C Data collection Period Accuracy Sensitivity As this sensor is temperature compensated and calibrated the humidity and temperature measurements can be easily taken It can be hooked up as in the connection diagram as given in Figure 3 5 for taking the measurements The detailed specifications are given in Table 3 5 3 3 Measuring Circuits We use Arduino as the processing unit The Arduino s analog pin can read values from OV 5V Hence the output voltages of the sensors are adjusted to be in this range for getting 12 accurate measurements The output of carbon dioxide sensor was 100 600 mV Hence amplification and filtering circuits were designed for this sensor For the other gas sensors output can be adjusted by selecting appropriate resistance The values of resistances selected are given in the section 3 2 along with sensor details The signal conditioning circuit of the carbon dioxide sensor consists of amplification and filter circuit Operational amplifier MCP6001 was chosen as the amplifier It supports rail to rail input and output voltage operation It has gain bandwidth product of IMHz and operates for single supply voltage ranging from 1 8V to 6V 2 All these features make it very apt for our purpose A low pass filter 1s used to filter the high frequency noise A capacitor of 100 nF was used as the filter The voltage source V2 in the conditioning circuit as shown in Figure
56. ual gas concentration 14 The appropriate devices for calibration were not available 1n the engineering laboratory nor any other laboratory on campus Considering the cost factors for buying these equipment we decided to test these sensors in a container and the test gases were obtained from common sources The container used was of size 24x13 1x16 8 inches manufactured by Hefty The Graywolf DirectSense IAQ 610 monitoring system was used as a standard measuring device It 1s a professional grade air quality monitoring system It comes in a kit which includes a tablet PC a probe USB cable for connecting the probe to the PC a tripod stand for the probe and an AC adapter The probe contains very accurate sensors which capable of detecting TVOC CO2 CO ozone temperature RH and dew point It has option for adding additional parameters 1f necessary The tablet has software called WolfSense PC for collecting graphing and storing the sensed data 15 The collected data from our system was compared with the Graywolf Sensor data and output equation for each sensor was modeled 50 6 2 Experiments Several experiments were conducted for analyzing the behaviour of the output of sensors Initially our system and Graywolf System were kept at normal conditions and readings were taken for about a week Another experiment was conducted by putting both the systems inside the test chamber and introducing a burnt paper Readings were taken at an interval of 5
57. uch as headache eye irritation fatigue dry throat sinus congestion dizziness and nausea Diagnosing sick building syndrome is difficult since many illnesses can cause the same symptoms Extremely high levels of some contaminants can cause more serious illness like chronic respiratory diseases heart disease and lung cancer including death 20 Therefore it is very essential to improve indoor air quality Here comes the need of building a monitoring system to detect the pollutants and its concentration as detection 1s the first step towards air quality improvement 1 2 Objectives of the Research Most monitoring systems available in market are very expensive and many of them have to be the taken to the spot of pollution to take the readings One of the professional monitoring systems available is Graywolf Direct Sense IQ 610 System It is very costly as it uses very accurate sensors In addition it 1s very bulky and has to be carried to the place which has to be monitored Another one available is wireless IAQ profile monitor by PPM Technologies Ltd This system uses several sensor nodes which can measure 3 to 7 parameters networked in mesh topology 22 But main problem for this system 1s its high price A low cost monitoring system 1s essential for making indoor air quality monitoring more popular Using wireless technology helps to collect data from remote areas and multiple locations simultaneously The aim of the research is to develop a
58. work It can go to low power mode called sleep mode 10 47 5 1 3 Implementation One of the modules is configured as a coordinator while the others are configured as routers There are many ways to configure the Xbee module We have used XCTU software from Digi International for configuring them as it is very convenient and user friendly However it is compatible only for Windows platform For programming it using this software Xbee 1s mounted on the Xbee shield which is plugged on the Arduino Uno board Then it can be programmed through the Arduino Uno s programming interface XCTU has mainly four tabs PC Settings Range test Terminal and Modem configuration The PC settings enable to select the COM port and set the radio parameters in order to configure the port It also has a test Query tab to check if the connections are made properly Using Modem configuration tab Xbee s parameters can be read and changed according to how we are going to use it It also allows us to modify the firmware versions The Range test is used to see how good the connection 1s established between two radios The Terminal tab allows access to the computer s COM port with a terminal emulation program Using this we can test 1f the Xbees are talking in the way we want 13 For building the network first a connection is established with Xbee module and PC using the PC settings tab Then modem parameters is updated Here we have set the Xbees as a coordinator or route
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