remote weather station

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1 RemoteWeatherStationUsingXBeeWirelessTransceivers

Remote Weather Station

Using XBee Wireless Transceivers

Christopher McCoy

CEN 4935

Dr. Janusz Zalewski

Florida Gulf Coast University

April 29, 2011


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Section 1: Introduction

Throughout the centuries, attempts have been made to produce forecasts based on

weather lore and personal observations (Earth Observatory).

People have always been fascinated with weather and its effect on their lives. This

fascination naturally led to a desire for prediction. With all the ways we are affected this

prediction would make life much easier. The NASA Earth Observatory claims Around 650

B.C., the Babylonians tried to predict short-term weather changes based on the appearance of

clouds and optical phenomena such as haloes. All throughout history there are examples of

people predicting the weather. The most basic of these predictions would temperature.

Benedetton Castelli wrote in 1638 about a device he had seen in Galileo's hands around1603 (Middleton). Galileos design incorporated a container to hold water as well as a glass

tube. When the water temperature changes the water rises or falls accordingly. Over the next

few hundred years the design was refined and liquid changed to more accurately judge the

temperature. These refinements resulted in the thermometer we know today.

To truly predict the weather the barometer was invented.

Evangelista Torricelli invented the mercury barometer in 1643 and today's mercury barometers

are much like those of the 17th century (Palmer).

A barometer measures the air pressure. Low pressure tends to produce cloudy, rainy conditions

while higher pressure tends to have fewer clouds and results in a fair weather trend. Granted this

only gives us a few hours or at most a day or two but this was a giant step forward from what

was available previously.

Another term that is commonly associated with the weather is humidity. Humidity is the

measure of the amount of water vapor in the air. The higher the humidity, the heavier the air

feels. When the temperature is higher humidity actually make it feel hotter than it really is. To

measure humidity an instrument called a hygrometer is used.


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A hygrometer is an instrument used to measure the moisture content or the humidity of

air or any gas (Bellis).There are numerous types ranging from ones that use hair (the hair extends

or contracts depending on the moisture content) to more complicated ones that use two

thermometers. One thermometer is exposed to the air while the other is submerged in water.

Based on the readings from each thermometer a table is then used to compute the humidity.


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Section 2: Problem Description

This project is a continuation of one started in fall of 2009 by Bradd Konert. He first

built a wireless weather station consisting of a Arduino weather microcontroller, XBee wireless

transceiver, LED display and a small solar panel to run the station and charge a series of AA

batteries.

My goal is to expand upon the work that he completed and gain a complete

understanding of the hardware used. In addition I will create a software based user interface to

display the incoming sensor data.

However, the weather station is not in working condition. Several of the connections

have been removed or disconnected. The batteries are currently dead. The documentation on theway the station was constructed is available but the markings are somewhat unclear.

Numerous attempts to repair these problems failed completely. As a result, a new

Arduino 2560 Mega board and SHT15 Temperature and Humidity sensor were ordered. These

items have then been used to complete this project instead of the original components. As a

result of these unforeseeable failures the updated goal is to connect, program and verify the

wireless network using these new parts.


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Section 3: Design Solution

Section 3.1: Original Design Solution

The original solution is outlined below. The images show the weather station, weather

sensors, XBee transceiver mounted to Arduino 2560 Mega board, solar panel and rechargeable

battery pack.

Figure 3.1: Current state of the interior of the weather station.

As you can see from the above picture most of the wires are disconnected or not in their proper

location. Some of the soldering also looks to be bad and in need of repair.


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Figure 3.2: Exterior view of weather station. February 10, 2011

Inspecting the outside there doesnt appear to be any physical damage. However, until

the station is functioning there is really no way to know if the LED display and switches are in

working order. There are no cracks or scratches on the solar panel so it appears to be structurally

intact.

The system was also tested using a volt meter to ensure the solar panel was generating

enough electricity to power the system. Test results showed the power generated was more than

sufficient for our needs.


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Figure 3.3:Wiring diagram provided by Dr. Zalewski. Obtained originally

from Bradd Konert.

Above is the provided wiring diagram that I am in the process of trying to use to rewire the

weather station.


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Section 3.2: Modified Design Solution

As a result of the problems found with the original hardware I was forced to order

replacement parts and modify the project. The revised solution implements a more basic version

of the original. The components consist of:

1. the Arduino 2560 Mega microcontroller board (Figure 3.2.1)2. XBee shield mounted (Figure 3.2.2)3. SHT15 Temperature/Humidity sensor (Figure 3.2.3)4. XBee Pro transceiver mounted on a host development board (Figure 3.2.4)

The assembled components are shown in figure 3.2.5.

Figure 3.2.1: Arduino Mega 2560


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Firgure 3.2.2: XBee on shield

Figure 3.2.3: SHT15 Temperature and Humidity Sensor


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Figure 3.2.4: XBee Pro on development board

Figure 3.2.5: Assembled Components


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Section 4: Implementation

Section 4.1: Hardware Assembly Attaching Sensor and XBee Shield to Arduino

Connecting the sensor to the microcontroller is a simple and straightforward process (see figure

4.1.1).

1. Begin by connecting the VCC pin on the sensor board to the 5V pin on the Arduinomicrocontroller. This provides power to the sensor. No soldering is required.

2. Next connect the GND on the sensor board to the GND port on the microcontroller, nextto the 5V pin.

3. Connect the DATA pin on the sensor to pin 9 on the microcontroller.4. Connect the SCK (System Clock) pin to pin 8 on the microcontroller.

The actual sensor connected is shown in Figure 4.1.2 and the connected XBee is shown in Figure

4.1.3.

5. Figure 4.1.1: Wiring Diagram


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The XBee shield communicates with microcontroller through 6 pins in the center of the

microcontroller. Simply line up the pins and gently press the shield onto the microcontroller.

Due to the alignment of the ports and pins on both the shield and microcontroller there is only

one way for these to connect.

This is all that is required to interface the sensor and the Arduino microcontroller.

Figure 4.1.2: Sensor connected to microcontroller


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Figure 4.1.3: Sensor and XBee shield connected to microcontroller


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Section 4.2: Software Implementation

This implementation is written in C and uploaded to the Arduino microcontroller using

an IDE provided by Arduino. An explanation of loading this code is located in the testing

section. The operation of the software is illustrated in the flowchart shown in Figure 4.2.1.

Figure 4.2.1: software operating flowchart

Below is the software implementation that is loaded on the Arduino microcontroller.

int dataPin = 9;

int sckPin = 8;

void resetSHT()

{


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pinMode(dataPin,OUTPUT);

pinMode(sckPin,OUTPUT);

shiftOut(dataPin, sckPin, LSBFIRST, 255);

shiftOut(dataPin, sckPin, LSBFIRST, 255);

digitalWrite(dataPin,HIGH);

for(int i = 0; i < 15; i++){

digitalWrite(sckPin, LOW);

digitalWrite(sckPin, HIGH);

}

}

//Specific SHT start command

void startSHT()

{




digitalWrite(sckPin,HIGH);

digitalWrite(dataPin,LOW);

digitalWrite(sckPin,LOW);




}

void writeByteSHT(byte data)

{




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// digitalWrite(dataPin,LOW);

shiftOut(dataPin,sckPin,MSBFIRST,data);

pinMode(dataPin,INPUT);

//Wait for SHT15 to acknowledge by pulling line low

while(digitalRead(dataPin) == 1);


digitalWrite(sckPin,LOW); //Falling edge of 9th clock

//wait for SHT to release line

while(digitalRead(dataPin) == 0 );

//wait for SHT to pull data line low to signal measurement completion

int i = 0;

while(digitalRead(dataPin) == 1 )

{

i++;

if (i == 255) break;

delay(10);

}

}

//Read 16 bits from the SHT sensor

int readByte16SHT()

{

int cwt = 0;


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unsigned int bitmask = 32768;

int temp;




for(int i = 0; i < 17; i++) {

if(i != 8) {


temp = digitalRead(dataPin);

// Serial.print(temp,BIN);

cwt = cwt + bitmask * temp;


bitmask=bitmask/2;

}

else {


digitalWrite(dataPin,LOW);




}

}

//leave clock high??


return cwt;

}


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int getTempSHT()

{

startSHT();

writeByteSHT(B0000011);

return readByte16SHT();

}

int getHumidSHT()

{

startSHT();

writeByteSHT(B00000101);

return readByte16SHT();

}

void setup() {



// connect to the serial port, sends data to the XBee

Serial.begin(9600);

Serial.println("Resetting SHT...");

resetSHT();

}

void loop () {

delay(2000);

Serial.println("Starting Temperature/Humidity reading...");

int temp = getTempSHT()*0.018-40;


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Serial.print("Temprature(F):");

Serial.println(temp);

temp = -4.0 + 0.0405 * getHumidSHT()+ -0.0000028 * getHumidSHT()* getHumidSHT();

Serial.print("Humidity:");

Serial.print(temp);

Serial.println("%");

}


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Section 5: Testing

Section 5.1: XBee Configuration (***Optional***)

This section is only relevant if you are using older XBee transceivers. By default each

should communicate with no additional configuration.

1. With the sensor disconnected mount the XBee shield to the Arduino microcontroller.2. The two transceivers should work with no configuration. If they do not continue on to

step 3.

The following steps were obtained from http://antipastohw.blogspot.com/2009/01/xbee-

shield-to-xbee-shield.html.

3. Download X-CTU from Digis website:http://www.digi.com/support/productdetl.jsp?pid=3352&osvid=57&tp=4&s=316

4. Put both Arduinos in Reset.5. Attach a USB cable from one arduino to Computer "A". Attach the other USB cable to

the other arduino and Computer "B". Open X-CTU.

6. Go to the "Modem Configuration" tab... set the Modem: XBEE to "XB24-B" AND setthe Function Set to "ZNET 2.5 ROUTER/END DEVICE AT"

7. Next is the Networking and Addressing Parameters...8. PAN ID = 1111 (Figure 5.1.1)


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Figure5.1.1:Step8

9. Destination Address High = 13A200 (I found this out by typing "AT" commands into aterminal program... first type in "+++" the xbee will return an "OK" you are now in

command mode... if you type "ATSH" then "" (enter), the xbee will give you it's own

high address (source address) ) (Figure 5.1.2)


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Figure5.1.2: Step9

10.Destination Address Low = 403E2502 (I found this out by typing "AT" commands into aterminal program) (Figure 5.1.3)


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Figure5.1.3:Step10

11.Click the "Write" button on the Modem Configuration tab and wait for the XBee toprogram

12.If some funny error comes up... click the button on the xbee shield and try to program itagain

13.Go to the "Modem Configuration" tab on computer B... set the Modem: XBEE to "XB24-B" AND set the Function Set to "ZNET 2.5 COORDINATOR AT (Figure 5.1.3)


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Figure5.1.3:Step1314.Next is the Networking and Addressing Parameters for the other XBee.15.PAN ID = 111116.Scan Channels = 15 (not sure if this is even needed)17.Channel Verification = 018.Destination Address High = 13A200 (I found this out by typing "AT" commands into a

terminal program... first type in "+++" the xbee will return an "OK" you are now in

command mode... if you type "ATSH" then "" (enter), the xbee will give you it's own

high address (source address) )

19.Destination Address Low = 404A4FC4 (I found this out by typing "AT" commands into aterminal program)

20.Broadcast Radius = 0


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Section 5.2: Arduino, Sensor and XBee Testing

1. Assemble the components as shown in section 4.2. Download Maxstream development board drivers from

http://www.digi.com/support/kbase/kbaseresultdetl.jsp?id=2138

3. IftheArduinoIDEisnotcurrentlyinstalled,downloadfromhttp://arduino.cc/en/Main/Softwareselectingthecorrectoperatingsystemfromthelist.

4. Once assembled go to the computer and open the Arduino software.5. Create a new sketch (Figure 5.2.1)

Figure 5.2.1: New sketch creation


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6. Copy the code from section 4.2 to the sketch window.7. Once the code is copied choose go Tools, Board and ensure that the Mega 2560 is

selected (Figure 5.2.2).

Figure 5.2.2: Proper board selection.


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8. Lastly press the reset button on the microcontroller and then the upload button on theArduino IDE (Figure 5.2.3).

Figure 5.2.3: Upload button.

9. Once the upload is complete a message will print in the black section at the bottom. Ifthere is a problem it will also be listed here.

10.Open the serial monitor (Figure 5.2.4) and you should see temperature and humidity databeing printed (Figure 5.2.5).


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Figure 5.2.4: Serial monitor button used to monitor results


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Figure 5.2.5: Correct results.

Section 5.3: Testing Comments

One thing to note in this testing. It appears that the XBee shield attached to the Arduino

microcontroller is failing. There are times where it is extremely difficult to get the transceiversto interface or the transmission stops for no apparent reason. Bradd Konert stated in his

documentation that an overvoltage damaged the temperature sensor on the USB weather board in

his station. This is likely the cause of this problem. At this time I would continue to monitor this

situation and possibly obtain a new shield and transceiver before continuing this project.


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Section 6: Conclusion

This project has been eventful. I started off by attempting to reconstruct the original

weather station created by Bradd Konert and encountering all the hardware components that

ultimately were defective. I learned a great deal about connecting components using a

breadboard and in turn testing them using a voltage meter. It was disappointing that the weather

station was never restored to working order but in the same instance it was a great experience

attempting to repair it.

Once I ordered and received the replacement parts I was shocked at how powerful the

Arduino microcontroller was. In researching the hardware the sheer number of uses these boards

have is staggering. Connecting the sensor, programming the board and setting up the XBee

network were challenging yet rewarding once it was complete.

Arduino claims that the XBee adapters work with basically no setup. In my experience

this was not the case. In speaking with Arduino I was told that these units are an older model

and that it is the newer models that require little, if any, configuration.

Future contributions to this project would be the ability to monitor this hardware

configuration remotely through either a downloadable application or a dedicated webpage.

Integrating a graph to plot previous sensor reading would also be desirable so that the user could

use the past and present data to predict future developments.

I would also advise looking into upgrading the weather sensors to the SHT15 USB

Weather Board from Sparkfun (http://www.sparkfun.com/products/9800). This board features

Absolute barometric pressure accurate within +/-150 Pascal, Relative humidity accurate within

+/-2%, Temperature accurate within +/-0.3 degrees C and an Ambient light sensor (analog

level). This would greatly increase the amount of data obtainable and give the user a much more

detailed representation of the current environment.


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Section 7: References

1. Earth Observatory. Weather Forecasting Through the Ages. NASA.Visited: Feb 10, 2011. http://earthobservatory.nasa.gov/Features/WxForecasting/wx2.php

2. Albert Van Helden. The Thermometer.Visited: Feb 10, 2011. http://cnx.org/content/m11978/latest/

3. Chad Palmer. How a Barometer Works. USA TodayVisited: Feb 10, 2011. http://www.usatoday.com/weather/wbaromtr.htm

4. Severino. XBee Shield to XBee Shield Communication.Visited: April 5, 2011. http://antipastohw.blogspot.com/2009/01/xbee-shield-to-xbee-shield.html

5. Arduino. Arduino XBee ShieldVisited: April 5, 2011. http://www.arduino.cc/en/Guide/ArduinoXbeeShield

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