Wireless Indoor Climate Sensor. D.M. van t Hof, A.T. van Rijs

Transcription

1 Wireless Indoor Climate Sensor Wireless Communication at Ultra Low Power Electronic Instrumentation Laboratory

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3 Wireless Indoor Climate Sensor Wireless Communication at Ultra Low Power For the degree of Bachelor of Science in Electrical Engineering at Delft University of Technology June 25, 2012 Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) Delft University of Technology

4 Copyright c Delft University of Technology (EEMCS) All rights reserved.

5 Delft University of Technology Department of Electircal Engineering, Mathematics and Computer Science (EEMCS) The undersigned hereby certify that they have read and recommend to the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) for acceptance a thesis entitled Wireless Indoor Climate Sensor by in partial fulfillment of the requirements for the degree of Bachelor of Science Electrical Engineering Dated: June 25, 2012 Supervisor(s): Dr. Ir. M.A.P. Pertijs Ir. Z.Y. Chang Reader(s): Dr. ing. I.E. Lager Prof. dr. ir. A.J. van der Veen

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7 I lovingly dedicate this thesis to my parents, who supported me each step of the way Dave van t Hof I dedicate this thesis to my family and friends, especially to Mom and Dad for instilling the importance of hard work and higher education. to my grandma, and grandpa for encouragement. to Nanette for encouragement - may you also be motivated and encouraged to reach your dreams. Alex van Rijs

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9 Preface As part of the Bachelor program Electrical Engineering of Delft University of Technology (EEMCS), a group project should be performed. The project described in this thesis is about a wireless indoor climate sensor. This climate sensor consists of an ultra low power temperature and humidity sensors provided by NXP and is partially developed by the electronic instrumentation laboratory of the Department of Electrical Engineering. The project was carried out by six students and is divided into three subgroups. One subgroup has investigated energy harvesting, while another researched the possible low power microcontrollers. We performed research in ultra low power transceivers. Since this product needs to be entirely wireless, the sensor will need an internal power source or another way to harvest energy. This means that the amount of power available will be small. For this reason, the product must have an ultra low power microcontroller and transceiver. The program of requirements can be found in chapter 3. If readers are interested in the potential wireless protocols, chapter 4, will satisfy their curiosity. Those interested in the reviewed ultra low power transceivers are referred to chapter 5. Furthermore, this chapter will cover the reasons we chose the XBEE Series II as an ultra low power wireless transceiver. Since displaying the measurements is as valuable as measuring the environment, we dedicated chapter 6 to the possible displaying options. Chapter 7 shows the measurements performed. Finally, our conclusions and recommendations can be found in chapter 8. During our research, a couple of people have helped us. We would like to thank the following people: Dr. Ir. M.A.P. Pertijs and Ir. Z.Y. Chang for the accompaniment and the formation of the project. Dr. Ir. G.J.M. Janssen for the help with calculations during the research. Ir. A.C. de Graaf for the technical advice he gave during the research. Ingmar Jager, Jan Angevare, Jeroen van Straten and Franklin van Putten for the fine collaboration during the Bachelor graduation project.

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11 Abstract The required product is a wireless indoor climate sensor. It is an autonomous sensor that transmits several parameters concerning its environment wirelessly. The product will be used to demonstrate a number of energy efficient sensors. The electronic instrumentation department at Delft University of Technology developed these sensors in association with NXP. Since the desire to communicate information wirelessly in an energy efficient way existed, several options could be explored. First a wireless protocol had to be chosen. Thereafter, a hardware solution had to be found in order to implement the chosen protocol. Lastly, the information had to be displayed on a computer screen. This thesis investigates six wireless protocols that can transmit information. The investigated protocols are Bluetooth, ZigBee, Rubee, UWB, Z-Wave and the well known Wi-Fi. In order to choose the right option, several criteria were set up. First of all, the system had to be entirely wireless. Therefore, the power consumption had to be as low as possible. Moreover, the program of requirements stated that the transmission distance had to be at least five meters. After searching for suitable wireless protocols for this assignment, the hardware had to be chosen. The SX1212, XBEE series II, ATmega128RFA1 and CC430xxxx were found as potential solutions. The same criteria that were subjected to the wireless protocols were applied to these hardware solutions as well. Furthermore, the ease of hardware implementation was added as well as the ease of software implementation. Additionally, the knowledge available at EEMCS about these solutions was appended to the criteria. The measurements had to be displayed after setting up the wireless communication. The measurements could be displayed on a website, an app or a computer screen. The measurements could have been stored locally as well as externally. Safety is one of the criteria used to choose a display solution. This was why locally storing the measurements was preferred. However, the recent popularity for apps was a criterion for choosing the method of displaying the information as well. The ZigBee solution was chosen, because it was most suited for this project. Rubee, UWB and Wi-Fi were abandoned, because those protocols do not meet the specifications. ZigBee uses less power than Z-Wave and therefore, is chosen above Z-Wave. The fact that former researchers encountered problems while setting up a connection between two Z-Wave modules was added to the argumentation. Bluetooth can have either a short range or a high output

12 vi Abstract power to transmit. Since the short range was considered too short, Bluetooth was abandoned as well. Moreover, ZigBee had been developed to transmit a low amount of data in a low power consuming way. Hardware had to be chosen after finding a suitable protocol. The XBEE series II was chosen from the hardware solutions. A low amount of data had to be sent and the XBEE series II was the least power consuming of these solutions while sending a low amount of data. Moreover, the XBEE series II was the easiest to implement. There were several options to display the received data. Since the data had to be received by a computer, displaying it on a computer screen was chosen. The data was displayed in the console in which the program was written. Moreover, an internet connection is not mandatory. However, it was chosen to develop an app as well. This is because an app can be viewed anywhere at any time. The current running through the system was measured in order to check if the requirements were met. The system appeared to have an average current consumption of 50.8µA. This consumption would be sufficient for the system to run autonomously for a year. Furthermore, it was necessary to check if the system was able to transmit over at least 5 meters, since the program of requirements stated this demand. The measurements showed that the system was able to transmit over 40 meters, which was enough.

13 Table of Contents Preface Abstract iii v Glossary xiii List of Acronyms xiii List of Symbols xiii 1 Introduction 1 2 Subdivision of tasks among theses System block diagram Task subdivision Program of Requirements on the Wireless Indoor Climate Sensor Usage Requirements Requirements According to the Ecological Situation of the System s Environment System Requirements Installation Requirements Project Requirements Known Wireless Protocols Properties of the Wireless Protocols Bluetooth ZigBee Wi-Fi Rubee Ultra Wideband (UWB) Z-Wave Choice and Justification for the Wireless Protocols

14 viii Table of Contents 5 Hardware Possibilities for a Transceiver Properties of Possible Hardware Solutions Current Consumption Transmission Distance Ease of Hardware Implementation Ease of Software Implementation Choice and Justification for the Hardware Possibilities Possibilities to Display the Data Data Storage Software on Computer App for Android and idevices Displaying on Website Choice and Justification for the Display Possibilities The System Website App Measurements on the Wireless System Transmission Distance Current Consumption Conclusion and Recommendations Conclusions Recommendations for further Research Bibliography 37 A Matlab Files 41 A-1 Matlab Code to Calculate the Energy Consumption A-2 Matlab Code to Calculate the Transmission Range

15 List of Figures 2-1 Block Diagram of the to be Designed System Bluetooth Protocol Stack SX1212 vs. XBEE series II vs. CC430Fxxxx vs. ATmegas128RFA The system The measurements as shown on a website WiSense app Transmitting a Single Measurement Transmitting a Single Measurement and Several Resends

16 x List of Figures

17 List of Tables 4-1 Summery of the Technical Specifications from Bluetooth[1] Bluetooth Power Classes[2] ZigBee Specifications [3][4] Summery of the Technical Specifications from ZigBee[1] Summery of the Technical Specifications from Wi-Fi[1] Advantages & Disadvantages Hardware Specifications for each Solution Transmission Distances in Free Space [5][6] Advantages & Disadvantages

18 xii List of Tables

19 Glossary List of Acronyms USB SDP L2CAP RFCOMM PCB PIN LMP 2-FSK WPS WAP FLL DCO MCLK Universal Serial Bus Service Discovery Protocol Logical Link Control and Adaption Protocol Radio Frequency Communication Printed Circuit Board Personal Identification Number Link Management Protocol 2 State Frequency Shift Keying Wi-Fi Protected Setup Wireless Access Point Frequency Locked Loop Digitally Controlled Oscillator Master Clock LPM3 Low Power Mode 3 AP FFD RFD RAID UWB Access Point Full Function Device Reduced Function Device Redundant Array of Independent Disks Ultra Wideband

20 xiv Glossary List of Symbols λ d G AR G AT G F S n P RX P T X R b t x I RX I sleep I T X Wave Length Distance in meters Receiver Antenna Gain Transmitter Antenna Gain Free Space Gain Number of Bits Receiver Sensitivity Tranmitter Output Power Bit Rate Time Amount of samples Receiver Current Sleep Current Transmitter Current

21 Chapter 1 Introduction The department of electronic instrumentation has partially developed an ultra low power chip, which measures the temperature, humidity and light intensity. A group of six bachelor students has been assigned to a project to develop an indoor demonstrator, which communicates with a computer wirelessly. The group was divided into three subgroups. The first group performed research in energy harvesting. The second group researched ultra low power consuming microcontrollers. The last group investigated possibilities to transmit and receive data wirelessly in a ultra low power consuming way. According to [7], the term wireless means that no wires are used for communication. Ever since Thomas Edison patented the first wireless system in 1885 [7], a lot of developments have been made in wireless systems. Many protocols have been developed since The intention of this project is to develop a prototype, which implements this chip. This demonstrator has to be entirely wireless. The power available will be limited and therefore, a low power consuming transceiver has to be chosen. The subject of this thesis is wireless communication in a low power environment and displaying the information sent over the wireless network. Since this all together is quite a challenge, it is divided into three sub problems. The information gathered during the literature survey will be used to eliminate these three sub problems. Wireless protocols are used to make sure the data is transmitted and received correctly. Hence the following question can be formulated: What wireless protocol should be used in order to transmit and receive data? Another question arises after finding a solution to the first problem. This question is: What hardware will be used to implement this protocol? After finding a solution to the second problem, a wireless network can be set up. When the data arrives correctly at the receiver, it still needs to be displayed on a screen. The third question is about the multiple ways the data can be displayed: How will the data be displayed, and in which ways can this be achieved? In order to meet certain demands, a program of requirements is essential. The program of requirements will be set up in consultation with the supervisors. Chapter 3 outlines the requirements the demonstrator has to satisfy to. In chapter 4, a span of six known wireless protocols will be given. This chapter will discuss their properties first. Thereafter, decisions

22 2 Introduction made will be discussed. When the protocol is chosen, different types of hardware, which suit the program of requirements, can be found. A span of currently available transceivers will be shown in chapter 5. Furthermore, an explanation will be given on how they work, and why a particular transceiver is chosen. When the connection is set up, the received information has to be displayed on a computer. This can be done in different ways. Chapter 6 will cover the possibilities of displaying the information on a computer. Additionally, it will discuss the choices made. In order to compare the actual values to the values agreed in the program of requirements, measurements have to be performed. Chapter 7 will discuss these measurements. From these measurements, conclusions can be made about whether the solutions meet the requirements. These conclusions can be found in chapter 8 along with recommendations for future research.

23 Chapter 2 Subdivision of tasks among theses As stated in the introduction, the development of the sensor node was subdivided into three main tasks: design of the control unit for the sensor [8], the development of the energy system [9]. The third task is covered by this thesis and will discuss the development of the wireless system. Each task was carried out by a group of two students, and these groups would each write a thesis about their task. This chapter describes the reasoning behind this task division. It may be useful to refer to appendix 3 for the system requirements while reading this chapter. 2-1 System block diagram The purpose of the designed system is to control the MIST1431 sensor and transmit the measurement data wirelessly to a computer. Furthermore, the sensor module has to be wireless in terms of power supply as well. From these specifications, the block diagram shown in figure 2-1 was made. The functions of the modules are described in the following paragraphs. Figure 2-1: Block Diagram of the to be Designed System

24 4 Subdivision of tasks among theses MIST1431 sensor The MIST1431 sensor block consists of the actual sensor and any necessary additional components or support systems required for correct sensor operation. Control This block is in charge of configuring and controlling the MIST1431 sensor and the wireless transmitter or transceiver. If bidirectional wireless communication is used, the control block is also in charge of processing any commands given by the computer. Finally, the control block is in charge of placing the system in sleep mode when a sample has been processed and waking it up again when a new sample is to be made. Transmitter and receiver or transceivers These blocks are in charge of respectively sending and receiving data wirelessly from the sensor module to the computer. As the data is to be given to the transmitter by the control block processed on the computer, no intelligence or understanding of the data packets is required in this block. Power supply This block is in charge of somehow supplying energy to the sensor module. As stated in the requirements, it must last at least a year without any form of service. Computer The computer is only required to present the sensor measurements to the user. If bidirectional communication is implemented, the computer may also be used to send commands to the sensor module. 2-2 Task subdivision As the system is to be designed in a group of six students and time is limited, a proper subdivision of design tasks was necessary. As an additional constraint to the project was that three theses were to be written, the team was split into three groups of two students each. The first group would be in charge of the design, implementation and documentation of the sensor and control blocks. Additionally, this group would be responsible for writing and documenting all software for the control block and the computer, although, due to time constraints, the tasks of doing the actual programming were divided among the entire team. The resulting thesis is [8]. The second group would be in charge of the design, implementation and documentation of the power supply for the sensor module. The resulting thesis is [9]. The third and final group would be in charge of the design, implementation and documentation of the wireless communication system and protocol resulting in this thesis. The reasoning behind this specific subdivision was that the three tasks were expected to take approximately equal amounts of time to complete. Additionally, they could be completed in parallel as their design is largely independent of one another.

25 Chapter 3 Program of Requirements on the Wireless Indoor Climate Sensor The following sections define the demands of the supervisors. The requirements stated below apply to the whole project. They do not apply to the wireless communication only. In the requirements below, the following definitions apply. 1. Sensor - the sensor module to be designed. 2. Host - the system, which the sensor sends its data to. 3. Sampling rate - the rate at which the sensor takes sensor value samples. 4. Transmission rate - the rate at which the sensor transmits (previously recorded) sensor data. 3-1 Usage Requirements [1.1] The product must measure at least temperature and humidity. More measured quantities are encouraged. [1.2] All communications between the sensor and the host must be done wirelessly. [1.3] The product must function autonomously in terms of energy supply. [1.4] If a battery is used, the user should be notified when the battery needs to be replaced. [1.5] The measured quantities should be presented on a computer.

26 6 Program of Requirements on the Wireless Indoor Climate Sensor 3-2 Requirements According to the Ecological Situation of the System s Environment [2.1] The product must function indoors. [2.2] The transmitter frequency, bandwidth and output power must fall within Dutch regulations. [2.3] The product must be unobtrusive within its operating environment, i.e. it should not draw attention to itself. 3-3 System Requirements [3.1] The sensor must have at least two operating modes in terms of sampling rate and transmission rate: a demo mode and a normal mode. In demo mode, the sample and transmission rate must be at least once per second. In normal mode, the sample and transmission rate must be at least once per minute. [3.2] The operating mode must be selectable using a jumper or switch on the sensor. Being able to set the operating mode wirelessly is nice to have. Being able to set more sampling and transmission rates is also nice to have. [3.3] If a battery is used, the sensor must operate without battery replacement for at least a year. This requirement assumes the sensor runs in normal (not demo) mode. [3.4] The range for wireless communication must be at least 5 meters. [3.5] Having the possibility to set minima and maxima for the measured quantities is nice to have. If such a limit were to be exceeded, the sensor should wirelessly transmit the current sensor data regardless of transmission rate. [3.6] To measure the temperature and humidity, the sensor chip developed by the Electronic Instrumentation Department at Delft University of Technology and produced by NXP must be used. [3.7] The chip mentioned above must be visible and influenceable during a demonstration. For instance, it must be possible to breathe on or touch the sensor to demonstrate that the measured quantities indeed change on the screen in such a case. [3.8] The system must deliver the measured data in such a way that it does not reduce the accuracy of the sensor chip(s) used. 3-4 Installation Requirements [4.1] It must be possible to install the product without changes to the environment.

27 3-5 Project Requirements 7 [4.2] The installation must be as simple as inserting a battery and installing some software on a computer. In other words, it should be "Plug & Play". It is acceptable if something like a USB dongle is required for communications. [4.3] Replacing a battery must be possible within a minute. 3-5 Project Requirements [5.1] All software written for this product must be well documented. [5.2] All hardware designed for this product (circuits and circuit board layout) must be well documented. [5.3] Writing platform independent software is encouraged. The "platform" is defined here as being the operating system for PC based software and the microcontroller (architecture) used for hardware based software/firmware.

28 8 Program of Requirements on the Wireless Indoor Climate Sensor

29 Chapter 4 Known Wireless Protocols The subsections in section 4-1 describe six low-power protocols that exist today, and are able to send information wirelessly. Each section summarizes the technical specifications and properties as the power consumption, connecting issues, network structure and the ease of implementing this protocol in a low-energy environment. Developing a new protocol would require an exceptionally long time and can be considered a project of itself, therefore, only existing protocols will be examined. 4-1 Properties of the Wireless Protocols This section describes six wireless protocols to be chosen from. The more relevant protocols will be discussed in more detail Bluetooth The Bluetooth technology has been developed for low cost implementations, which require a high data rate. The Bluetooth Alliance created a new version, Bluetooth 2.0, after entering the market with Bluetooth 1.0. This second version of the Bluetooth technology has widely been implemented in devices, such as cellular devices and laptops. The Bluetooth alliance started developing Bluetooth 3.0, but this was not widely adopted. Bluetooth is developing a new version, version 4.0. This version of Bluetooth will become a towering competitor for ZigBee (section: 4-1-2), as its specifications seem to become better than ZigBee s current specifications. However, according to [10] Bluetooth 4.0 has only been integrated in the IPhone 4(s) and some other devices. Unfortunately, no known modules are available. Therefore, only Bluetooth versions lower than 4.0 will be considered, from now on called Bluetooth. Bluetooth uses the 2.4GHz band, which is allowed to be used in the Netherlands[11]. In years past, Bluetooth made a substantial breakthrough due to the largely scaled implementation within small devices as well as laptops.

30 10 Known Wireless Protocols Technical Specifications Table 4-1, recites the technical specifications of the Bluetooth protocol. The standards are clarified in the following paragraphs. Table 4-1: Summery of the Technical Specifications from Bluetooth[1] Standard IEEE spec. Frequency band Max signal rate Nominal range Nominal TX power Number of RF channels Bluetooth GHz 1 Mb/s 10 m 0-10 dbm 79 Protocol The Bluetooth stack (figure: 4-1) has some mandatory protocols, which need to be implemented. Some of which are: Link Management Protocol (LMP), Logical Link Control and Adaption Protocol (L2CAP) and the Service Discovery Protocol (SDP) protocol. Furthermore, the Bluetooth stack has some protocols, which are widely implemented: Radio Frequency Communication (RFCOMM) and HCI[12]. Figure 4-1: Bluetooth Protocol Stack Power Consumption Devices equipped with the Bluetooth technology can have three possible power classes. A device cannot change its power class, since the power class is maintained by the hardware. The three power classes are listed in Table 4-2. Even though, there are three power classes, the third power class is exceptionally uncommon due to its limited range[2]. Table 4-2: Bluetooth Power Classes[2] Class Class 1 Class 2 Class 3 Maximum Output 100 mw 2.5 mw 1.0 mw Power 20 dbm 4 dbm 0 dbm Operating Range 100 meters 10 meters 1 meter In addition to the operating mode a Bluetooth device can be put into three different power saving modes. These modes allow inactive Bluetooth devices to conserve power. The three

31 4-1 Properties of the Wireless Protocols 11 modi are: Sniff Mode The device keeps listening to signals from other devices that want to exchange data. The main difference between this mode and the operating mode is that the frequency of monitoring its environment is much lower. Hold Mode The device maintains its current association with the main device. The clock signal is still running, and devices are synchronized. In this mode, the device will not initialize new connections, nor will it monitor its environment for other devices. Park Mode If this mode is active, the device will not be registered with any of the members in the piconet 1 and will lose its network address until it gets awakened. Operating Mode The operating mode is the fastest mode, but is not the most energy efficient. Parking a device leads to the loss of the network connection. If the master is in need of using this device, the connection needs to be set up. Therefore, it would take longer to take this device back into usage and ready to send, as when the device would have been in hold mode[13]. Connecting Issues If the device is triggered to send data, it uses the LMP to send it. This protocol sends information on how to pair the devices. If the user previously set a password, the LMP protocol will make certain that this information is received and transmitted to the right device. The received data will be parsed by the Link Manager 2. During the first initialization, both parties (receiving and transmitting) need to enter a Personal Identification Number (PIN) code. If the PIN codes correspond, a link key will be created. This key can be used for future communication. Network Structure Figure 4-1 illustrates Bluetooth s basic cell. This basic cell is based on a piconet. In a piconet, one main apparatus connects to at least one device. The main apparatus is called the master, can connect up to 7 clients, called slaves[14]. A property of this network structure is that all the devices transmit on the same channel and frequency. Implementation The figure of the Bluetooth stack shows that the Bluetooth stack consists out of several protocols each in demand for memory. The Bluetooth stack is 250 KB in size. The higher amount of memory leads to a higher price for a single module. These modules can be purchased online 3 and are easy to install if one has some programming experience The Link Manager communicates with the Link Controller that knows the supported services. The Link Manager is a piece of software. 3

32 12 Known Wireless Protocols ZigBee ZigBee has been developed specificly for low power features. It has a typical current consumption of 30 ma in TX mode and 3µA in sleep mode[3, p. 134]. Compared to both Bluetooth and Wi-Fi this is remarkably low. It can operate in three frequency bands, namely 2.4GHz, 868MHz and 915MHz. Since the 915MHz band is assigned for military purposes in the Netherlands[11], it is not an option to use that band. The ZigBee specifications also show that this band can be used in the United States of America only[15][16]. ZigBee satisfies the law condition if the 2.4GHz band or the 868MHz band is used. ZigBee modules can have ranges starting from 10 meters up to 100 meters[16]. Table 4-3: ZigBee Specifications [3][4] solution I T X (ma) I sleep (µa) range (m) ZigBee Technical Specifications Table 4-4, enumerates the technical specifications of the ZigBee Protocol. The technical terms will be further discussed in the paragraphs of this section. Table 4-4: Summery of the Technical Specifications from ZigBee[1] Standard ZigBee IEEE spec Frequency band 868/915 MHz; 2.4 GHz Max signal rate 250 Kb/s Nominal range m Nominal TX power (-25) - 0 dbm Number of RF channels 1/10; 16 Protocol The IEEE-standard is the foundation the ZigBee protocol is built on. This standard describes the Physical layer and the datalink layer. Power Consumption ZigBee is well known for its low power consumption. This low power consumption is realized by some smart functions. ZigBee devices have a sleeping mode in which they reside most of the time. It is not expected that these devices send a lot of data in a small time. ZigBee equiped devices are devices that do not need to send a lot of information and therefore, can go into a sleep mode. Each device has the ability to go into or wake up from sleep mode. Zigbee can wake up within 15 ms and go into an operating mode.[17] Connecting Issues ZigBee networks are extremely easy to set up and the connection is similar to connecting to a Wi-Fi network with Wi-Fi Protected Setup (WPS). The two ZigBee devices can be paired by clicking on a button on the receiver as well as the responder. It is, unnecessary to say, that the two need to be within communicating distance from each other.

33 4-1 Properties of the Wireless Protocols 13 Network Structure One of the many positive things about Zigbee is that the network layer can set up and maintain connections with the network. This same layer has several extra tasks, such as addressing routing and securing the data connection. The other wireless solutions consume more power, because they cannot organize and maintain the network layer. Because ZigBee is equipped to handle these tasks, a complete implementation would be cheaper since extra equipment to handle these tasks has become superfluous. Implementation ZigBee has a stack just as Bluetooth has one. The main difference is the size of the stack. The ZigBee stack consists of 32 KB voor the Full Function Device (FFD) and 4 KB for the Reduced Function Device (RFD). ZigBee devices are provided with a single 8 bit processor leading to lower costs for the implementation. If the developer / programmer uses pipelining to increase the effectiveness of each clock cycle, it could reduce the power costs drastically. An external microcontroller can do calculations that the 8 bit ZigBee processor was supposed to do. This would mean the ZigBee module can reside longer in sleep mode, and therefore, will consume less power.[18] Wi-Fi If a wireless network measures up to the specifications in the family, the term Wi-Fi can be linked to it. Back in 1999 an organization carrying the name Wi-Fi Alliance 4 created the term Wi-Fi and it was a matter of time before this term was included in the encyclopedia. The Wi-Fi Alliance tests new products for inter-operability. If a product, complies to the requirements and passes all the tests, it is allowed to carry the label Wi-Fi certified [19]. Table 4-5: Summery of the Technical Specifications from Wi-Fi[1] Standard IEEE spec. Frequency band Max signal rate Nominal range Nominal TX power Number of RF channels wi-fi /a/b/g 2.4 GHz 5 GHz 54 Mb/s 100 m dbm 14 (2.4 GHz) Technical Specifications Protocol The current family consists of six wireless modulation technologies that use the same protocol. In current households, the a, b and g are most common n started to saturate the market and can soon be considered common as well. These technologies function on the (free to use) 2.4 GHz band. The downside of this band is that many other wireless devices use the 2.4 GHz band, which can lead to interference. 4

34 14 Known Wireless Protocols Power Consumption The Wi-Fi protocol has been designed and optimized to propagate through a great deal of space as opposed to other technologies as Bluetooth or Zigbee. Since users of this protocol are in demand of attaining a high as possible bit rate over the largest possible space, Wi-Fi has a fairly high power consumption. This option is not considered a low-energy efficient transceiver, due to this fairly high power consumption. Connecting Issues These systems are widely used in corporations, households and public areas. The bulk of users demands a fast and stable connection. These demands induce more options and more security settings to be made as apposed to the other technologies. The sending/receiving Access Point (AP) needs to be configured the right way to ensure a stable connection. Network Structure A Wi-Fi network is configured to operate in two different ways: infrastructure mode or ad hoc mode. If the network is configured in such way that it operates in ad hoc mode the packages will not need to be controlled centrally, but the devices can communicate with each other in a direct way. The other mode is an infrastructure mode, which lets the devices connect via a Wireless Access Point (WAP). This WAP acts as a bridge between the wired and wireless network. Implementation One can choose to purchase a predesigned and programmed module. This can save a lot of time and for small quantities, a lot of money. If chosen to purchase these modules, implementing them into the systems is the last thing to be done. In the case of developing a large number of devices, it is cheaper to build the products in-house than to outsource it. Keep in mind that Wi-Fi is created for large propagation and high data rates, leading to a more complex system Rubee A slightly less known protocol is RuBee. RuBee uses frequencies up to 450 khz and it uses the IEEE standard[20]. According to [20] the data rate is 9600 bits/s with transmission distance of approximately 3 up to 15 meters. The given transmission distances, would occur at 131 khz as this is the optimal operating frequency for RuBee[21]. However, 3 meters would not be sufficient to meet the program of requirements (chapter: 3). This option is excluded, due to insecurity of measuring up to the distance requirements Ultra Wideband (UWB) UWB is a new technology with the ability to send packages with a speed up to 1 GB/s. These packages are sent over an enormously wide band starting from 3 GHz, and running up to 10 GHz. This technology is designed to send a lot of data over a small distance. This technology does not work with a continuous carrier wave, but sends packages of waves [22]. Since the UWB technology transmits over a wide range of frequencies, the chance of interfering with other devices is large as apposed to other technologies[23]. The telecom law states that not all bands are free to use in the Netherlands [11]. Furthermore,

35 4-2 Choice and Justification for the Wireless Protocols 15 if a legal transmission bandwidth is chosen, a requirement is imposed that limits the output power. This limited output power decreases the transmission distance and makes it uncertain to achieve the minimum 5 meters of transmission distance. Therefore, due to the uncertainty of meeting the requirements with regards to the transmission distance and the fact that this protocol cannot function freely within its operating band, it is chosen to reject this solution and will not be considered a valid option Z-Wave The Z-Wave technology is mainly used in home-automation applications. Z-Wave is built upon the Zigbee technology, and therefore, has the same protocols as Zigbee maintains. A prime difference is that Z-Wave networks are unsecured, and therefore, sensitive to malicious objects. A group of Bachelor students showed in their thesis that Z-Wave performs less or equal to Zigbee[24]. This is among others due to the bit rate used by Z-Wave. Therefore, Z-Wave will not further be discussed. 4-2 Choice and Justification for the Wireless Protocols The previous sections covered the technologies Bluetooth, ZigBee, Wi-Fi, RuBee, UWB and Z-Wave. The program of requirements states that a solution has to be found that consumes as little energy as possible. Wi-Fi is ruled out, since it is developed to perform over a large distance with a high data rate, leading to an inefficient power usage. RuBee, UWB and Z- Wave have been ruled out in the previous section. This exclusion leaves two options to be chosen. It is shown that the consumption values of Bluetooth and ZigBee differ slightly, but the current consumed receding in sleep mode is considerably higher for Bluetooth than for Zigbee. Therefore, when comparing Bluetooth to ZigBee it is clear that ZigBee is less power consuming and easier to implement. Furthermore, it is known that Bluetooth enabled devices have problems when an object is placed in the transmission field. Bluetooth is designed to operate over a short distance. Concluding, Zigbee is a better solution than Bluetooth. Table 4-6 shows the advantages and disadvantages for each solution. Table 4-6: Advantages & Disadvantages Property Bluetooth 2.0/3.0 ZigBee Wi-Fi Rubee UWB Z-Wave Distance Interference (3x) Power (2x) Datarate Total

36 16 Known Wireless Protocols

37 Chapter 5 Hardware Possibilities for a Transceiver In chapter 4, the wireless protocols were discussed. It is shown that ZigBee is the least power consuming of these protocols. Therefore, Zigbee hardware solutions will be discussed. However, two different hardware solutions, which use none of the protocols in the previous chapter, will be discussed as well. Four hardware solutions have been found. The first solution is the SX1212, which is a transceiver only. It is made by Semtech. The second solution is the Atmel ATmega128RFA1, which is a ZigBee transceiver and microcontroller together in one chip. Thirdly, the XBEE series was found. The XBEE series are transceiver modules, which use ZigBee. The XBEE series are produced by Digi International. There are two versions of this module, the series I and II. Lastly, the CC430xxxx was found. Again, this is a transceiver and microcontroller together in one chip. The CC430xxxx is manufactured by Texas Instruments. In order to choose a suitable transceiver, the potential hardware solutions should be tested against the program of requirements. First, the properties will be discussed in 5-1. The properties of each solution will be compared in section 5-2. This section will discuss the choices made as well. 5-1 Properties of Possible Hardware Solutions This section gives a brief overview of the properties, which the decision is based on. First the current consumption will be discussed. Thereafter, the transmission distance will be reviewed. Thirdly, the ease of hardware implementation will be taken into account. Lastly, the ease of software implementation will be discussed Current Consumption One of the most fundamental properties, is the current consumption of the product. According to the program of requirements (chapter 3), the sensor module has to function autonomously

38 18 Hardware Possibilities for a Transceiver in terms of energy supply. This means that there is a limited power source. Since the sensor module needs to be operational for at least one year before changing the battery, the sensor module, the transceiver and protocol have to be as low power consuming as possible. ATmega128RFA1 The ATmega128RFA1 has a low transmit(i T X ) and receive current (I RX ) (table 5-1). This I T X was chosen, because -2.5dBm output power would give a large enough range[25]. The lowest sleep current (I sleep ) this transceiver could use is 250 na[25, p.4]. The bit rate was chosen to be 1,000 kbit/s as this was the highest bit rate with a safe transmission distance. Unfortunately, the datasheet of the Atmel ATmega128RFA1 was not clear about the wake up procedure from the deep sleep mode. Therefore, it was assumed that it is not possible to get the processor out of deep sleep mode unless an external interrupt is given. An external interrupt cannot be given in deep sleep mode, since the only external input could be from the transceiver, which is asleep as well. Therefore, the assumption was made that the deep sleep mode could not be used. This automatically meant only the regular sleep mode of this processor must be used, which has a current consumption of 4.1 ma. Later, it was found that multiple deep sleep modes were present on the ATmega128RFA1 and that some of them did not need an external interrupt to wake up. Using a crystal to get a reliable clock to wake up, the deep sleep mode would have a current consumption of 1µA. These values were found after the hardware was chosen and therefore could not be used for making a decision for the hardware. SX1212 The SX1212 is a transceiver, which is ultra low current consuming. It has a low transmit current of 25mA, a low sleep current of 2µA and a low receive current of 3 ma [26]. This is also shown in (table: 5-1). However, the maximum bit rate is low, which could be the bottle neck, because this means that the SX1212 needs to take more time to transmit a certain amount of data. XBEE series II As said previously, XBEE has developed two different series, the series I and series II. The XBEE series I has a I T X, which is 5mA higher than the I T X of the XBEE series II. Besides, the I sleep of the series I is ten times higher than the I sleep of the series II. The I RX is 10mA higher as well[27][5]. Therefore, the series II would be preferred over the series I. Although the I T X and I RX of the Series II are higher than the SX1212, the I sleep of the XBEE series II is lower. This means that which transceiver of these two is using the least current depends on the bit rate and the amount of bits sent. The actual values can be found in table 5-1. CC430Fxxxx The CC430xxxx can transmit over several frequencies. The 868MHz frequency was chosen here as this is the lowest power consuming mode. The lowest I T X possible in this frequency band is 18 ma at an output power of 0 dbm. If a higher output power was chosen, the I T X will be 15 ma higher, which would be unacceptable. The sleep mode was chosen in consultation with other members of the group, since they did research in microcontrollers. Since an external crystal could be attached to the Printed Circuit Board (PCB), only the upper block of the clock system of the CC430 needs to be kept enabled[28, p.81]. This meant the Frequency Locked Loop (FLL), Master Clock (MCLK) and the Digitally Controlled

39 5-1 Properties of Possible Hardware Solutions 19 Oscillator (DCO) could be disabled as could be concluded from this schematic. The DCO s dc-generator could be disabled as well. Hence the chosen sleep mode was Low Power Mode 3 (LPM3). The LPM3 has a current of 2.2 µa[29]. The baud rate was chosen to be 250 kbaud/s as the other baud rates consume the same I RX. The datasheet[29] stated the modulation technique for 250kbaud/s is 2 State Frequency Shift Keying (2-FSK), which uses two states. Therefore, the bit rate was equal to the baud rate. At the receiver side, two options were available. On the one hand, the sensitivity could be set to -40 dbm with a I RX of 15mA, but on the other hand the sensitivity could be set to -100dBm with a I RX of 16mA. The latter one was chosen as the sensitivity of -40dBm and an output power of 0 dbm would give a calculated range of 4 meters (calculations of transmission range will be further explained in the next subsection). This did not meet the requirements, so -40dBm sensitivity was not considered to be an option. Table 5-1: Hardware Specifications for each Solution Hardware I T X (ma) I sleep (µa) I RX (ma) bit rate (kbps) ATmega128RFA1[25] ,000 SX1212[26] XBEE series1[27] 45 < XBEE series2[5] 40 < CC430F[29] Transmission Distance The second crucial property, was the transmission distance. According to the program of requirements (chapter 3) the transmission distance had to be at least five meters. For a demonstrator this range is compelling. However, it might be better if the product can transmit over a wider range and maybe even through a wall. The range has been calculated for every solution. The following mathematical formulas (both 5-1 and 5-2)[30] were used to calculate the distance d a transceiver can cover (using 2 transceivers of the same type). The G AT and G AR are the antenna gains of the transmitter and receiver respectively. G F S is the free space gain. P T X and P RX are the output power of the transmitter and the sensitivity of the receiver respectively. λ is the wave length of the signal, which is related to the frequency. The provided distances by datasheets and the calculated distances can be found in table 5-2. P RX = G AT G F S G AR P T X (5-1) ( ) λ 2 G F S = 4πd (5-2) ATmega128RFA1 The datasheet of the ATmega128RFA1 does not say anything about the distance it can transmit over. This means a calculation has to be made in order to compare the Atmega with the other solutions while looking at this property. The ATmega128RFA1 has an external antenna, which can be achieved by installing a trace on the Printed Circuit Board (PCB). In this case, a dipole antenna could be used[31], since a trace is similar to a wire. The antenna gains of both the transmitting and receiving

40 20 Hardware Possibilities for a Transceiver antenna are equal to 1.5 [30, p.581]. The maximum output power is 3.5 dbm and the receiver sensitivity is -100dBm. At a frequency of 2.4 GHz, a distance of approximately 2,100 meters can be covered. It has to be kept in mind that this is the transmission distance in free space. The calculation may apply if the antenna is ideal and if it is placed on high buildings as almost no reflections will occur there. In practice, the antenna will most likely give a loss of several db instead of gain. Moreover, reflections from the ground will give a loss of several db as well. However, it is clear that the ATmega meets the required distance. The transceiver satisfies the other requirements. SX1212 The SX1212 has an external antenna as well. This could be a dipole antenna as well. Using the RX sensitivity and TX output power in equations 5-1 and 5-2, the outcome was about 40,000 meters. The RX sensitivity will be lower than the -104 dbm stated in the datasheet[26], because the bit rate chosen in the previous section is approximately 6 times higher. This seemed to be an unrealistic range, especially compared to the others. However, together with the maximum output power of 12.5 dbm, the low frequency and the low bit rate, made the calculated range more realistic. The 40,000 meters of transmission range will never be achieved for the same reflections and antenna loss, the ATmega128RFA1 had as well. Moreover, the RX sensitivity will be lower. Nonetheless, these calculations made the transmission distance of 600 meters, which Semtech claimed[6], realistic. XBEE series II According to the datasheets of both XBEE series I[27] and II[5], the Series I has a smaller range it can transmit over. Besides, section shows that the XBEE series II will be used. Therefore, the XBEE series I is left out in further comparisons. According to [5] the transmission distance is about 120 meters in free space. The calculations, using equations 5-1 and 5-2, result in a transmission distance of about 1,500 meters. The difference between these values can be explained due to several causes. First of all, the antenna is about a quarter of the wavelength at 2.4 GHz. This means the antenna most likely will not have a gain, but probably a loss of several db. Besides that, the definition free space is not specific enough. If both the two transceivers are on high ground, quite a far distance can be covered. However on the ground, there will be a lot of reflections. These reflections will give a loss of several db as well. CC430Fxxx The datasheet of the CC430Fxxx says nothing about the transmission distance it can cover. Therefore, the equations previously meant, can be used again. Like the ATmega128RFA1, a trace on the PCB is taken as the antenna and the outcome would be under ideal circumstances. Again, it has to be kept in mind that the antenna most likely will give a loss of several db, instead of a gain. Besides, reflections from the ground and buildings will give a loss as well. The calculated distance that this transceiver could transmit over is about 4,000 meter at 868MHz. This range is calculated with the maximum output power and sensitivity as chosen in the previous section and a bit rate of 250kbit. It is clear that this satisfied the requirements.

41 5-1 Properties of Possible Hardware Solutions 21 Table 5-2: Transmission Distances in Free Space [5][6] Hardware solution Datasheet Transmission Distance (m) Calculated Transmission Distance (m) SX1212 ± ,000 XBEE series II ± 120 1,500 ATmega128RFA1-500 CC430Fxxx - 4, Ease of Hardware Implementation Another notable thing, which can be discussed, is the ease of hardware implementation. There is little time to create a working model. Choosing a solution, which is easy to use and easy to implement on a hardware level, will help significantly. For this reason, the ease of hardware implementation is another property, which is indispensable while making a choice for the hardware solution. Moreover, the ease of testing should be noted as well. The possibility to find bugs would be better, if there were more time to test. Thus, in the case of this research, it was necessary to choose components, which were easy to implement. ATmega128RFA1 The ATmega128RFA1 is a single chip. The fact that it is a transceiver and microcontroller together in one chip will decrease the amount of components needed on the PCB. However, the chip has an exposed pad. This means it has to be put in an oven in order to be attached to the PCB. In order to test whether the chip is functional, software needs to be written first. A property of the XBEE series II is that it is easy to connect to a computer through Universal Serial Bus (USB). Therefore, this device can be used at the receiver side. Since both the ATmega128RFA1 and the XBEE series II used ZigBee, they can communicate with each other. SX1212 The SX1212 is a transceiver only. This means it would need a microcontroller in order to function properly. The SX1212 has an exposed pad as well, which means it has to be placed in an oven in order to be attached to the PCB. Besides that, a circuit has to be developed around the SX1212. Again, software needs to be created for the microcontroller, before testing is possible. This should be developed for the receiver side as well. Again, at the receiver side a connector connects the PCB with the computer. XBEE series II The XBEE series is a wireless module only. It needs a microcontroller in the circuit in order to function properly. Sparkfun has developed a PCB for the XBEE modules. The PCB can be connected to the USB port of a pc and the XBEE modules can be installed using the female headers on the PCB. This is why the XBEE series is easy to connect to a computer. The software for the XBEE series II already existed, because the XCTU software has been developed in the past. Therfore, testing the XBEE series is quite easy and can be done in earlier stages compared to other solutions. It would be a plug & play solution. CC430Fxxx The CC430Fxxx is a microcontroller and transceiver together in one chip. This is just like the ATmega128RFA1, except for the fact that there are packages of this chip,

42 22 Hardware Possibilities for a Transceiver which do not have an exposed pad. This means it does not necessarily need to be placed in an oven in order to attach it to the PCB. Like the ATmega and the SX1212, software needs to be created in order to be able to test. Again at the receiver side it should be possible to connect the PCB with the computer Ease of Software Implementation The last property discussed was the ease of software implementation. This property has been discussed with the microcontroller group, because they would write a lot of the software needed. Especially, if chosen for a transceiver and microcontroller together in one chip, they would have to write most of the software. The members of this group have told that the ease of software implementation was about the same for each of the solutions. Therefore, it was assumed that for each solution, the ease of software implementation was equal to the other solutions. 5-2 Choice and Justification for the Hardware Possibilities The previous section discussed the advantages and disadvantages of each solution. This section discusses the decisions made. In order to get a decent view on the current consumption, the charge used per year has been calculated first. Thereafter, a table is made in which the advantages and disadvantages are placed. Then a choice will be made. Calculation of Charge Consumed per Year To find out an estimation about the charge each of the hardware solutions consumes, a model has been made in Matlab (Appendix??). This model contains the transmit current, sleep current and receive current for each hardware solution(5-1). Moreover, the bit rate was included. The functions 5-3 and 5-4 show the current consumption, which is estimated. n was the number of bits sent per minute, t was the time in seconds, and R b was the bit rate in bits per second. There was assumed that the amount of transmitted bits per minute was the same as the amount of received bits per minute. This can be done, because the amount of bits used to send the temperature and humidity to the receiver is low. Since every layer of the OSI-model adds a header[32, p.15], most of the bits sent would be used for headers most likely. t = n R b (5-3) q(n) = ((t I T X) + (t I RX ) + ((60 2 t) I sleep )) [Ah] (5-4) 3600 Please note that these calculations gave an estimation of the charge consumption only and that the real charge consumption would be higher as the transceiver most likely used a higher current than the sleep current while waking up. Besides, the occurrence of packet loss was not included in the calculations. The charge consumption for each of the solutions was shown in figure 5-1.

43 5-2 Choice and Justification for the Hardware Possibilities 23 As shown in figure 5-1 the XBEE series II, the SX1212 and the CC430Fxxxx were remarkably close to each other when looking at the charge consumption. There was an intersection point at about 450 bits/minute. However, the ATmega128RFA1 was less charge consuming than the other options. This would mean that the ATmega128RFA1 had an advantage on this property, but this was found to late. The CC430Fxxx and SX1212 used more charge than the XBEE series II in the region under 450 bits/minute. However, the charge per year calculation of the CC430Fxxxx included the sleep current of the microcontroller as a whole. Figure 5-1: SX1212 vs. XBEE series II vs. CC430Fxxxx vs. ATmegas128RFA1 Choice and Justification for the Hardware Possibilities With the information in the previous paragraph and the information in the previous section, it was possible to choose the most proper solution. Since current consumption, which is directly related to power consumption, was most important for the demonstrator, this property would add weight to the scale twice. There would be taken into account that there was knowledge about the XBEE series II at EEMCS, because if problems would occur, there would be engineers available to help solve the problems. Table 5-3 shows the advantages and disadvantages for each solution. It was concluded from table 5-3 that the XBEE series II was the best solution to be implemented to the demonstrator. Table 5-3: Advantages & Disadvantages Property SX1212 XBEE series II ATmega128RFA1 CC430Fxxx Power (x2) Distance Ease of Hardware Implementation Ease of Software Implementation Knowledge at EEMCS Total

44 24 Hardware Possibilities for a Transceiver Financial Costs What may be found remarkable is that the financial costs for each of the solutions have not been discussed. Hardware costs have not been included in the program of requirements (chapter 3). Therefore, the financial costs for hardware have not been included in our choice.

45 Chapter 6 Possibilities to Display the Data The previous chapters show how the information is retrieved. However, what is the value of having information if it cannot be shown to the user? The measured data that has been delivered to the server needs to be displayed. This chapter covers a span of possibilities on how to solve this problem. The program of requirements states that the system is required to display the measured data to the client. There are several possibilities to comply to this requirement. 6-1 Data Storage After the Indoor Climate Sensor sends the information, the receiving device will process this data and send it to the computer. This can be achieved by connecting the hardware solution to the Universal Serial Bus (USB) port of the computer. Note that, other ways exist as well on connecting the device to the computer. Once the received data has been processed, it has to be stored. There are solutions to store the data locally as well as externally. Local Storage Measured data can be stored locally. Local storage does not require an internet connection, and therefore, is faster than other storage solutions. The data can be stored locally on a HDD/SDD. Other methods as an USB-stick are considered a viable solution as well, and accounts for storing the data locally. The size of the measurements is about 1.5 MB per month, therefore, the measurements will not consume a significant part on the local disk. External Storage Storing the data externally has the advantage that the information can be viewed independent of the location. The data is handled and stored on a server which is connected to the Internet. Since most servers are installed in Redundant Array of Independent Disks (RAID) configuration, and are configured to backup frequently, the data is less sensitive to HDD errors.

46 26 Possibilities to Display the Data If it is desired to view the data independent of location, it is advised to store the data externally. A PHP script stores the received data into a MySQL server. According to [33] a simply written code secures the data better as apposed to a tedious code, because it is better for keeping an overview. If the requirement to view the data independent of location lacks, storing the data locally would be a better option, since this is faster and does not require an internet connection to send data. 6-2 Software on Computer The data can be displayed to the user by means of a specifically developed program to monitor the data measured by the sensors. The software can be fitted to work with externally and locally stored data. Externally stored data 1, which is stored on a server connected to the internet, has a drawback that it is exposed to threats from the internet such as hackers. On the other hand, externally stored data is more user friendly since the data can be viewed without a desktop computer. 6-3 App for Android and idevices Everyone has the sense that right now is one of those moments when we are influencing the future Steve Jobs Mobile phones are turning into indispensable objects[34]. Sales are sky-high, and everyone is in need of a smart-phone. The large presence of smart-phones can be used to display the measured data. It is user friendly and can be used from anywhere within a house. The downside of an app is that it is not as easy to develop as opposed to software on a computer. It takes more time to develop as opposed to computer-based software. More time equals more costs in the business scheme! 6-4 Displaying on Website Nowadays, a significant percentage households have a connection to the internet[35]. A website can dynamically be created to show the user the current data. The freedom from a stationary computer makes this a convenient and reliable choice. 1 stored in a MySQL server

47 6-5 Choice and Justification for the Display Possibilities Choice and Justification for the Display Possibilities Chapter 3 states the criteria, which are tested against the displaying possibilities. It shows the requirements which need to be met by the project. It is noted that the measured quantities should be visible on a computer. After consulting the supervisors of this project regarding the conception of the term computer", the possibility for developing an app remained a valid option. Section 6-3 explicates the reason why an app for mobile devices is an asset to a company. It is chosen to develop a software application with the ability to run on a desktop computer2 as well as on a mobile device, due to the possibility of conceiving the term computer in another way than is described by the program of requirements The System As mentioned in the previous section, a choice was made to develop software to run on a computer as well as on a smart phone. The system is able to perform the measurements, and transmit them wirelessly. The system is displayed in figure 6-1. Once the data has been received, it can be monitored on a website (figure 6-2) or in an app (figure 6-3) which is available in the App Store under the name: WiSense. Figure 6-1: The system 2

48 28 Possibilities to Display the Data Website A website was developed for users to monitor the measurements without using a smartphone. Figure 6-2 shows what this website does. The website has a live connection with the database and is triggered every second for new data. This website is used to manage the current sensors associated to the account. Figure 6-2: The measurements as shown on a website App If the user has an idevice such as an ipod, iphone or ipad, the app can be downloaded from the App Store. This app, as shown in figure 6-3, has the ability to show the current measurements and monitor a history of the measurements. (a) Home screen (b) Temperature Figure 6-3: WiSense app