Sensitivity Of Watermark Sensor Computer Science Essay

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In order to test the reliability of the Read SD data LabVIEW and the SD code, a series of tests were carried out. Basically, three tests had been carried out which were tested on the difference of temperature, relative humidity, atmospheric pressure and soil moisture during the day and night time , measuring the water retention of different types of soil and the sensitivity of the Watermark sensor.

To ensure the accuracy of the readings, the Watermark sensor was placed in the soil upright with 12 cm depth in the soil for every test. For Watermark's sensitivity and different types of soil water retention testings, the temperature was kept to indoor room temperature of an average of 29.5366 oC. It is because the moisture of the soil is affected by soil texture, soil structure, organic matter, density of soil, surrounding air temperature, salt content, depth of soil and type of clay.

5.1.1 Sensitivity of Watermark Sensor

Watermark sensor responds to the soil water content. Noted that the Watermark had been placed in the water before the day of the experiment carried out to ensure the reliability of the code and sensor. The Watermark was placed upright in the soil. A hole of 12cm deep had been dug to place the sensor. The Watermark shown values of 48.43401 cbar when it had not being inserted into the soil yet. After that, the Watermark sensor was put into the wet soil. The readings displayed shown that the soil moisture was getting higher which almost hitted 0 cbar. The graphs shown the changes of the Watermark's readings. Graph 1 was displayed as the sensor measures the water content of soil in Hertz (Hz). However, in order to know the water retention of soil, centibar (cb) is used as it is the standard unit of measuring the soil moisture. Graph 1 was displayed and used to make a comparison with Graph 2. It was to ensure that the conversion was correct and give accurate readings to user.


Graph 1: Time vs Soil Moisture (Hz)


Graph 2: Time vs Soil Moisture (cbar)

5.1.2 Comparison of Parameters during the Day and Night

SD code was created and loaded into the Waspmote so that it was easier for the user to take the parameters outdoor. The Waspmote was placed at the same location in the morning, noon and night. From the Graph 3, it was clearly shown that temperature in the afternoon is the highest among the others which had an average of 34.20611 oC. Average temperature that taken in the morning was 30.78992 oC whereas the average temperature at night was 26.60665 oC.


Graph 3: Temperature taken on Thursday, 2 May 2013

To find out the difference of surrounding humidity during the day and night, Graph 4 was plotted. From the graph, it was clearly shown that the relative humidity at night was the highest which had an average of 72.05274%RH followed by relative humidity in the morning, 69.006%RH. Relative humidity at 12:46pm in the afternoon had the lowest humidity which was 60.88444%RH.

From the findings, it was proven that the temperature affects the relative humidity. The value of the relative humidity may be high for a lower temperature, less for a higher temperature as it denotes the ratio of the amount of water vapour actually present to the amount of water vapour required to saturate the air (for a particular temperature). In the other words, relative humidity shows the degree of saturation. Since the relative humidity depends on the saturation, the saturation can occur at any temperature. Hence,the variation of relative humidity is reversed from the temperature. If the temperature increases, the saturation level is also rises which means the air can hold more amount of water vapour and lead to less percentage of water vapour. Thus, relative humidity value drops. In short, the increase of temperature leads to less relative humidity value for the same amount of moisture content.


Graph 4: Graph of Relative Humidity in the Morning, Afternoon and Night

The Graph 5 below shown the atmospheric pressure in the morning, afternoon and night. It was clearly shown that the atmospheric pressure was quite constant for the whole day no matter during the day and night. The average values of atmospheric pressure at morning, afternoon and night were 108.6701 kPa, 108.4118 kPa, 108.3038kPa respectively.

Atmospheric pressure is the force per unit area exerted on a surface by weight of air above that surface in the atmosphere of Earth. Obviously, the surrounding factors like temperature and humidity do not affect the readings of the atmospheric pressure. The mean sea level pressure much affects the atmospheric pressure. Low pressure areas have less atmospheric mass above their location whereas high pressure areas have more atmospheric mass above their location. Likewise, atmospheric pressure decreases with increasing elevation.


Graph 5: Atmospheric Pressure in the Morning, Afternoon and Night

As the soil moisture sensor, Watermark measures the soil water content using Hertz in measuring unit, conversion was carried out. In order to know the water retention of a soil, centibar (cb) unit was used as it was the standard unit in measuring the soil moisture of soil. The readings of soil moisture that measuring in Hertz was used and displayed to make a comparison with the centibar conversion.

From Graph 6 and Graph 7, it was obviously shown that the soil moisture in the morning had the lowest reading which indicated that the soil held the most water content. The average value of the soil moisture of soil in the morning was 0.549694 cb. This result might due to the dew in the morning and the rain last night. In the afternoon, as the temperature rises, the soil was getting dry and shown an average value of 0.74293 cbar. When it came to night time, the soil had an average value of 6.520794 cbar. Althought the temperature was dropping, the soil moisture was decreasing as the soil had exposed to the hot weather in the afternoon that dried out the water content of the soil. However, the soil was still in the range of 0-10 cbar which indicates it was still saturated soil.


Graph 6: Graph of Soil Moisture (Hz) in the Morning, Afternoon and Night


Graph 7: Graph of Soil Moisture (cbar) in the Morning, Afternoon and Night

5.1.3 Experiment on Different Types of Soil Texture

There are several factors that affecting the soil moisture which are soil texture, soil structure, organic matter, density of soil, surrounding air temperature, salt content, depth of soil and type of clay. These factors can severely affect the soil water content of a typical soil.

Basically, there are three particle types of soil. The biggest particles are sand, the medium-sized particles silt and the smallest particles called clay. Particle types determine the soil's texture. There is more pore space, surface area and greater retention of water in a finer texture. In short, different types of soils have different retention of water. Hence, a comparison of water retention of Ultisols and Haplic Acrisols was carried out.


Ultisols are one of the twelve orders of soil taxanomy. Ultisols commonly known as red clay soils. They defined as mineral soils which contain no calcareous material within the soil. They have less than 35% base saturation throughout the soil. They have less than 10% weatherable minerals in the extreme top layer of soil.

Ultisols vary in colour from purplish-red to a bright reddish-orange. They are quite acidic and have a pH of less than 5. The colors of red and yellow result from the accumulation of iron oxide which is highly insoluble in water. Ultisols can have variety of clay minerals. They can be cultivated over a relatively wide range of moisture conditions. Ultisol was shown in Figure 27.


Figure 27: Ultisols used in the experiment.

Haplic Acrisols

An acrisol is a type of soil which is associated with humid and tropical climates. It is clay rich and often found in forested areas. Acrisol commonly can be found in old land surfaces with a hilly in wet tropical and monsoonal climates. Light tropical (rain) forest is the natural vegetation type. Acrisols are low fertility and toxic amounts of aluminium pose limitations to its agriculture use. Crops that can successfully cultivated include oil palm, rubber tree, tea, sugar cane if the climate allows. The Figure 28 below shows haplic acrisols.


Figure 28: Haplic Acrisols

In order to find out the differences between the soil moisture of Ultisols and Haplic Acrisols, a comparison graph was built. From the Graph 8, it was shown that Ultisols had higher retention of water than Haplic Acrisols. The average water content of Ultisols and Haplic Acrisols are 0.492311 cbar and 0.563679 cbar respectively.

However, there were fluctuations in measuring the soil moisture of Ultisols and Haplic Acrisols. At the beginning of the measurements, there were greater undulations. It might due to the time required for the water to go through the transmission section and into the measurement section of the sensor. In the Watermark sensor, the measurement section is isolated from the soil and so a finite amount of water must move from the soil through a transmission section before entering the measurement section in order for the sensor to respond to the changes in soil water potential. The time required for this water movement is a function of potential gradients and hydraulic conductivity within the soil and the sensor. Hence, the time required for the water to move into the measurement section was believed to cause the fluctuations.

From the graph, it was clearly shown that most of the readings fell at 0.56 cbar for Haplic Acrisols and 0.51 cbar for Ultisols. The soil moisture of Haplic Acrisols fell between the range of 0.5378 cbar and 0.6168 cbar which had a difference of 0.079 cbar. Meanwhile, the water retention of Ultisols fell in the range of 0.4325 cbar and 0.5114 cbar. The difference between the highest and the lowest readings of Ultisols were 0.0789 cbar. Thus, the errors that occurred in measurements were quite small.


Graph 8: The Comparison of Utilsols and Haplic Acrisols

5.2 Interfacing of MCP9700A, 808H5V5, MPX4115A and Watermark Using LabVIEW

Interfacing of MCP9700A, 808H5V5, MPX4115A and Watermark using LabVIEW was a method that used to read the sensor values online. After the code was loaded into the Waspmote, connected the Waspmote to personal computer using USB cable. COM Port and baud rate were selected to COM 15 (according to user's computer) and 38400 respectively. Graph 9,10,11,12 and 13 shown the online readings of temperature, relative humidity, atmospheric pressure, soil moisture in Hertz and soil moisture in cbar by using LabVIEW respectively.


Graph 9: Time vs Temperature (oC)


Graph 10: Time vs Relative Humidity (%RH)


Graph 11: Time vs Atmospheric Pressure (kPa)


Graph 12: Time vs Soil Moisture (Hz)


Graph 13: Time vs Soil Moisture (cbar)

5.3 Troubleshooting

There were lots of problems occurred when the Waspmote was used to take measurements. The major problems that faced in this project were SD card formatting, unknown symbols in the data files on SD card, headers loop continually and great fluctuations of waveform graph in LabVIEW.

5.3.1 SD Card Formatting

Waspmote has external support such as SD (Secure Digital) card. This micro-SD card is used to reduce board space to minimum. Besides that, it provides a more convenient and easier method for user to measure the outdoor parameters.

When formatting the SD card before using the Waspmote, there are some considerations to have in mind. Before formatting a SD card, the most important matter is to set the right size of the allocation tables to address the card properly. Waspmotes uses the FAT16 file system and can support cards up to 2GB. The information that Waspmote stores in files on the SD card can be accessed from different operating systems such as Windows, Mac-OS and Linux. Despite of selecting FAT16, if there is no indication when formatting the card, the OS will select a size between 12,16 and 32 bits.

If selecting the wrong size of allocation table to format the card, all the sensors values could not append into the SD card. It would also affect the readings displayed at the serial monitor as well. The header will keep looping and will not display all the sensors values. Figure 29 shown the error that occurred when selecting the wrong size of allocation unit size.


Figure 29: Errors that appeared on serial monitor when selecting wrong allocation unit size during formatting SD card.

Windows 7 only provided two types of allocation unit size which is 32 and 64 bits. However, the right value for formatting the SD card is 16b (FAT16). Hence, HP USB Formatter was used to format the SD card as shown in Figure 31. HP USB Storage Format Tool has a compact interface with options to select hardware, devices and Filesystems. It also has an entry area for volume label and checkboxes for formatting. The USB Format tool identifies the file type and compresses the files before formatting them. Clicked Start to reformat it and a pop-up will warning user that all the data on the drive will be lost. Proceed the process and the drive gets formatted in seconds. At last, eject the SD card and reinsert it into the Waspmote.

After that, switched on the Waspmote for a minute. Serial monitor would display all the sensor values properly with the header. All the data can be moved into the new reformatted drive. Figure 30 shown the result after formatted the SD card.

D:\5. Final Year Project\4.result\after plug into the soil (without soil+soak in water 30 minutes 7-730).png

Figure 30 Results shown on the Serial Monitor after formatted the SD card.


Figure 31: HP USB Storage Format Tool.

5.3.2 Unknown Symbols In The Data Files on SD Card

As in the code, the sensors values were defined as float numbers. However, when appending the sensors values into the SD card, it did not recognize the float numbers. It shown “?” in the file instead of printing the values of sensors. The temperature, humidity, atmospheric pressure, soil moisture values were converted to string in order to parse the value into the SD card. The formula used in float-string conversion was shown in Figure 32.


Figure 32: Float-string Conversion

5.3.3 Header Loops Continually

Besides the wrong selection of allocation unit size of SD card formatting, loose plug-in of USB cable into Waspmote board could also cause this type of error to be happened. The Waspmote kept printing the header as there was a loose end of the connection. Errors would pop-out at the bottom column of Waspmote IDE which written in red as shown in Figure 33. Once the cable was replaced with a new one, the problem was solved.

D:\5. Final Year Project\4.result\loose error.png

Figure 33: Loose end of the connection.

5.3.4 Great Fluctuations of Waveform Graph in LabVIEW

Timing is one of the important issues. The function of Wait until Next ms Multiple is used to synchronize activities. The rate of display data can be manipulated by adjusting the timing.

When reading the sensor values online through LabVIEW, user had to ensure that the time delay that set in the LabVIEW must match with delay that had been set in the Waspmote code. In Waspmote code, 6 seconds delay was set. It mean that the every 6 seconds, the sensors would take new measurements and the values would be then displayed on the waveform graph. If different time delay was selected, for instance 3 seconds, the readings would jump back to zero as the sensor could only take the measurement every 6 seconds. Figure 34 shown the results of setting the wrong time delay.


Figure 34: Results of setting the wrong time delay.

5.3.5 FTDI Drivers and VISA Driver Installation

Waspmote required integrated development environment (IDE) and driver in order to communicate between the Waspmote instrument and computer. Waspmote IDE was used to program Waspmote. C programming (instructions) could be verified in IDE before loaded into Waspmote's microcontroller. For Windows Vista and Windows Xp, it was important to install FTDI drivers so that the port on which the Waspmote board had been plugged in would appear in the "Device Administrator". If FTDI drivers was not installed, serial port configuration could not be carried out.

In computing, a device driver or software driver is a computer program that operates or controls a particular type of device that is attached to a computer. A driver typically communicates with the device through the computer bus or communications subsystem to which the hardware connects. A device driver simplifies programming by acting as translator between a hardware device and the applications or operating systems that use it. Hence, installation of VISA driver was needed. Without VISA driver, LabVIEW was unable to configure the setting of the serial port.



6.1 Conclusion

The goal of the project which was to build a system using serial communication to determine the temperature and relative humidity of air had been achieved. Student also able to construct and/or write C and LabView program which were capable to carry out measurements. Although there were some problems occurred, as stated in troubleshooting section, during accomplishing this project, student was still manage to solve them to make the project better. The measurement and graph plotting in the LabView could be carried out accurately and efficiently after troubleshooting had been done. The objectives of the project had been achieved.

6.2 Suggestion

In this project, most of the parameters had been monitored and analysed by using the connection of USB cable and saving the measurements into the SD card. However, there are still some better ways to get the measurements directly. Wifi module for the Waspmote platform could complete the current connectivity possibilities which enabling the direct communication of the sensor nodes with any Wifi router which available in any market. This radio allows Waspmote to send the information directly to any iPhone or Android Smart phones. Furthermore, the application of Wifi on Waspmote is believed to reduce the unnecessary procedure to load the program code into the Waspmote using USB cable once the Waspmote has been housed and placed in the field.

The application of Waspmote Wifi for both iPhone and Android platforms could be developed by installing the apps from App Store (for iPhone) or Android Market (for Android Smart phones) which allows Waspmote to connect to it. Instead of carrying the computer everywhere with the user to monitor the parameters, the Wifi module send the information directly to user's handphone.

Bluetooth module could also be carried out to send or receive the information directly. The Bluetooth radio module should has been specifically designed in order to scan up to 250 devices in a single inquiry. The main idea of setting up a bluetooth module is to be able to detect Bluetooth users in the surrounding area.