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SmartWatch Prototype

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C
Charlie Aylward

This document describes the design and implementation of a smartwatch prototype using inexpensive, commonly available components. Key features included are a touchscreen LCD for display and input, Bluetooth module for communication with a smartphone, and a wireless charging system for the battery. The prototype demonstrates the integration of these technologies and serves as a proof of concept for a basic smartwatch. Challenges encountered included inefficient screen updates, modifying Bluetooth code for notifications, and addressing differences in the charging module and Arduino voltages. The completed prototype functions as a basic smartwatch, displaying time and notifications from a paired phone.

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1  Abstract—This experiment provides a working prototype of a smartwatch using inexpensive, commonly found components. The device consists of an LCD with touch-input capability for the user, a Bluetooth module to connect and communicate to the user’s mobile device, and a battery system that extends battery life with the ability to be charged wirelessly. Designing this system provides the authors with the opportunity to work with the integration of software and hardware, and create a device that combines the aforementioned technologies in a working, proof-of-concept computer system. Furthermore, the experiment provides the opportunity to research existing and future technologies that could be applied to this prototype to bring a product to market. I – INTRODUCTION URRENTLY, there exists a large barrier to entry in the smartwatch market. Proprietary technology and licensing deals with OEM’s make the design of a compact, complete smartwatch very difficult. Larger components are used in the design as smaller customized components would require prior knowledge of desired pinouts, communication protocols, and planned schematics. The larger breakout board components also provide freedom to interchange components and experiment with different hardware designs to find the optimal setup. Furthermore, the physical materials required to create a complete watch (leather/metal band, links, glass, etc.) are not readily purchased and assembled. For these reasons, we decided that the best approach to this problem would be development of a prototype device that combines a few core features commonly found in current smartwatch devices. In our prototype, we implemented three core features: a touch LCD, Bluetooth communications, and wireless charging for the battery. Upon completion of implementing these features, we have a working platform to build from if time permits. These features alone comprise a basic computer system: a controlling unit with a data path, a user interface, and a means of communicating to external systems. With core functionality in mind, the design process actually allowed us to perform a lot of research into both current and future technologies relevant to the various fields. The design carries out as a parallel process. With three team members and three core functions to implement, each member works individually on an assigned component, with periodic meetings to facilitate the integration of the three into the final system. The LCD is programmed and calibrated to perform the functions necessary of a watch face, the Bluetooth module is tested and set up to work with the microcontroller to be able to connect and communicate with a paired handheld device, and the battery requirements for the system are calculated and implemented. This project is valuable to us for multiple reasons. First and foremost, it is a project that is feasible to complete in about 7- 8 weeks of limited time, and provides us with an opportunity to learn about different engineering disciplines and combine them into a computer system, and it is always good practice to work with new and emerging technologies to keep engineering skills current. Much of modern engineering design requires analysis of datasheets, application notes, pieces of code, etc., which are important skills to have. Furthermore, the various components being implemented in the system come from different fields of electrical engineering. These fields include microcontroller programming, power electronics, Bluetooth communications, and mobile software development. Beyond that, our research led us to understand how our prototyped system could be improved in the future. II – COMPONENT DESIGN This design combines readily available components into a system that performs three core functions commonly found in commercial smartwatches. The primary system functions include capacitive touch input, displaying of time and date, and notifications of messages received on a paired Smart Phone device. The Bluetooth protocol is used to facilitate communications between the system and a mobile device. The design of the system is broken down into three distinct sections, including a display module, Bluetooth module, and wireless charging module as shown in Figure 1. Fig 1. Components included in prototype smart watch design. The controlling unit is an Arduino Uno microcontroller, and it interfaces seamlessly with the Bluetooth Low Energy Shield for Arduino and the Adafruit TFT Touch Shield for Arduino to form the core of the watch electronics. A battery system is used to power the Uno (which connects power and ground pins of all three boards, thus powering them all) to allow for Smart-Watch Prototype Charlie Aylward, David Ritter, and Eric Rule C
2 mobility. The Arduino UNO contains the MCU controlling the rest of the system by the means of SPI and I2C communication protocols. The Arduino UNO serves as an ideal prototyping main controller as it provides a large array of digital and analog pinouts which can behave as inputs and outputs. The Arduino UNO also provides the other system components with a power source. Fig 2. Arduino UNO with labeled headers for connections to added modules. A – LCD Module An Adafruit capacitive-touch LCD screen provides an interactive user interface. The screen is 2.8”, has a 240x320 resolution, and utilizes 16-bit color [1]. It communicates with the Uno via SPI, runs off 3.3V, and draws approximately 100mA when updating [1]. Most important are the basic watch functions of displaying the time and date. These are found at the top of the screen, and are updated as often as possible. The rest of the screen is reserved for displaying incoming notifications, sent via Bluetooth from a paired mobile device, usually a smartphone. When the watch receives a notification, the microcontroller processes it and displays the correct message to the user. This LCD is much larger than would be necessary on a real smartwatch, and as such, would be replaced in the future. Reducing the size of the screen would not only reduce the overall power consumption of the device, but also allow for greater utilization of the screen. Some choices that would be considered when choosing a screen technology such as LCD, AMOLED, or e-paper would be pixel density, various color/brightness/contrast attributes, and power consumption. The e-paper screen is dim and plain, but consumes an incredibly small amount of power, allowing for greater battery life. Deciding between LCD and LED technologies would be a matter of pricing and performance. B – Bluetooth Module The RedBearLab BLE board is connected to the Arduino Uno for the prototyping of this system, and it contains the necessary hardware to implement a fully functioning Bluetooth module. It supports multiple operating systems and Bluetooth protocols [2]. The purpose of this board is to allow Bluetooth communication pairing between the system and a user’s smartphone, to receive useful data from it. To complete this transaction of data, the Arduino software is configured to wait for data once a device is paired. When it receives a signal indicating some useful data has been transferred, it communicates to the Uno via ACI [2], which is a modified version of SPI, to have the data processed accordingly. For instance, if the user receives an email on their phone, the notification is sent over Bluetooth to the BLE board, and then to the Uno, where it processes the notification and displays the correct graphic on the LCD. To distinguish between different types of notifications received by the phone, some software must be installed. For this project, the Android OS by Google is supported (in the future, Apple’s iOS would also be supported) and an Android application must be installed to facilitate communication. The Android application requests to pair with the smart watch prototype, and sends the correct information to the BLE board once paired. Figure 3 illustrates the packet flow between the smart watch and a connected smart phone. This custom Android software is partially taken from some open source code found on the Internet, but has been modified for custom use. Fig 3. Bluetooth pack flow diagram between prototype smart watch (RX) and connected Android smart phone (TX) Currently, the prototyped system allows for email, text message, and call notifications. In the future, support for more functionality would be implemented on both ends, such as the ability of the watch to send various sensor data to the paired phone. Beyond that, the Android application would be substantially updated to provide a more comprehensive interface. C – Battery Module There are multiple constraints to consider when running an embedded system off battery power. The battery must have sufficient voltage to keep all circuits running simultaneously, and account for supply drops at times of high current draw at peak operation. The amp-hour capacity of the battery must be
3 more than enough to allow the device to run for a desired amount of time to prevent unwanted shut-offs due to power consumption. Furthermore, the battery must be physically sized to fit in the packaging that will be used to house the device. These constraints require analysis of device power consumption at different periods of operation: low-current draw “idle” state and peak current draw when the user is operating the device frequently. The manufacturer of the microcontroller used in this design recommend a battery voltage range of 7V to 12V. The lower bound of 7V is required to prevent the 5V traces from dropping too low and the upper bound prevents a voltage regulator from overheating and burning up. The first instinct is to jump to a 9V battery as the solution; however, the 9V cells generally have low capacity, and a lot of its energy will be burned off as heat being dropped to the lower voltages required by the controller. Since the battery must also be wirelessly rechargeable, this eliminates the choice of any standard store-bought cells. Herein lies the issue of barrier to entry: without integrating the necessary components into a single, compact system (as done in modern smartwatches), the battery will be much larger than it would actually need to be. Many smartwatches currently available use small, efficient rechargeable batteries: an iFixit teardown revealed that the Apple Watch uses a 3.8V, 205mAh lithium-ion battery [1], and the Samsung Gear Live uses a 3.8V, 300mAh lithium-ion battery [2]. These batteries are allowed to be so compact because the rest of the circuitry is optimized for the device and there are no unnecessary components. Our project, being a prototype, will not be nearly as efficient, and a 9V rechargeable cell will be sufficient as a proof-of concept. To charge the battery wirelessly, a simple set of inductive coils with charging circuitry was purchased from Adafruit, and are used to recharge the battery. This coil supplies 0.5A at max power transfer, and as such is not an ideal charging system. The Apple watch has a receiving coil and charging circuitry built into the device [1] and greatly simplifies the wireless charging of its battery. If this design were to be taken further and improved to the point of being viable as a consumer good, the battery system would change drastically. First of all, if the entire system was optimized to fit in a single housing, the battery could be reduced to a much smaller size, most likely one of the common 3.8V solutions. The wireless charging kit would be optimized to support one of the current standards being developed (PMA, WPC, A4WP) and reduce in size, while being able to supply a higher current such as 1A. III - SYSTEM ARCHITECTURE The Arduino UNO serves as the system’s main controller, keeping track of connected devices and running the code, which provides the system with functionality. The Arduino UNO was a good fit for our needs as it offers multiple communication protocols and an abundance of digital and analog IO pins for adding devices. Along with the hardware benefits of the Arduino UNO, there are easy to use code libraries available for software development. Many attachable devices have manufacturer-developed API meant to interface the device with Arduino systems. Both the RedBearLab BLE Shield and the TFT LCD display offer example code and libraries for the Arduino UNO simplifying the software development process. Fig 4. System Component Setup showing connection methods for RedBearLab BLE Shield and TFT LCD Screen. The primary functionality for the prototype device includes time display, Bluetooth notifications, and wireless battery charging. Both time keeping and Bluetooth communication rely heavily on the software for correct operation. Bluetooth notifications specifically require a separate device such as a smart phone for the intended functionality. The goal of this project is to pair the prototype with an Android smart phone. The Android Operating System was chosen as it allows open source development. Communication with a smart phone requires that the phone have software enabling it to function properly. Smart phone applications serve this purpose and can also grab system information from the phone, such as notifications. With an application on the smart phone, the smart watch prototype system can successfully receive notifications from the connected smart phone via Bluetooth. Figure 5 shows the system block diagram with the smart watch modules and the Bluetooth-connected Android smartphone. Fig 5. Block diagram of system design and system interfaced with Bluetooth compatible Android smartphone. The software development process involved two main parts.
4 First, the Arduino microcontroller required the necessary code to keep track of time, communicate with the Bluetooth shield, and communicate with the touch screen display. Second, an Android application able to pull notifications from an Android smart phone and establish a connection with the Bluetooth shield on the prototype needed to be developed. The time keeping software utilizes the Arduino Time library. More specifically, the function “millis()” is an Arduino method that keeps track of the milliseconds after the initialization of the program code once loaded onto the Arduino. By setting the initial time in the code and using the Time functionality mentioned, the Arduino is able to serve as a clock. Using the TFT LCD display, the time can be output to the screen in a readable format showing the current time (up to seconds) and date. Software needed for communication with the RedBearLab Bluetooth shield and the Adafruit TFT LCD display was available in libraries from the respective manufacturers. This made the initial task of establishing connections simple and left only the programming toward our specific application. The Bluetooth shield did not require much initialization code beyond setting the broadcast name. With the name established, a single function calls begins the operation of the Bluetooth shield. Once in “operating mode”, another function call polls for devices requesting to be paired. Once paired, a separate function checks for data being sent along the connection toward the BLE shield. In this system, the Bluetooth transmission is unidirectional from the phone to the BLE shield. This setup is appropriate, as the prototype device only needs to receive Bluetooth information from the smart phone. If a notification is received over Bluetooth by the BLE shield, the microcontroller draws an indication graphic to the display. The interfacing to the TFT LCD display also requires minimal setup. The initialization involves drawing a background to the screen and creating the time display. After initialization, the display shows notification graphics and updates the time when triggered. Figure 6 shows the system’s software workflow. Fig 6. Software flowchart for the Arduino UNO microcontroller interfaced with the Bluetooth shield and TFT LCD display. IV – DISCUSSION OF RESULTS The working smartwatch prototype implements the three discussed functionality of LCD display, Bluetooth communication, and wireless charging for only $112.79 (see Appendix for BOM). While the user interface is primitive in design and functionality, the smartwatch displays the time and integrates Capacitive Touch functionality for changing the color of the Bluetooth notification icon. The Bluetooth communication is demonstrated with email notifications displayed to the LCD screen from an external Android phone (via a user created Android application). The wireless charging is integrated via a 3.3V LI battery that drives the entire Arduino based smartwatch system. Overall, the system behaves as discussed in the System Architecture section, and integrates the three components. A few of the issues encountered during implementation of the prototype follow.
5 A – Challenges with the LCD The sample code found on the Ardiuno website for the Capacitive Touch LCD display requires explicitly writing to each pixel or group of pixels on the LCD. Therefore each time the time display is updated, the previous time (or anything on the display) must be written over to erase the previous display. Because the sample code is not optimized, the writing and rewriting of something even as small as the time bar must be locally erased. The update or “loop” cycle cannot update fast enough for the Bluetooth and erasing the entire display every cycle. This bug was fixed by locally erasing the changes to the display rather than continuously refreshing the entire display buffer (erasing the entire display and rewriting to all the pixels). B – Challenges with Bluetooth The Arduino Bluetooth sample code found online utilized an Android application for communication with the Arduino BLE shield. However, the application originally required user input to change a set of LEDs. This code was modified to first display a notification and then access the Android notification outputs to trigger a display sequence (i.e. to display an icon on the LCD). The internal Android email notification flag required modifying the Android application to accept email notifications. This required both access permission on the Android operating system and integrating the notification to trigger the LCD icon display via Bluetooth. C – Challenges with Wireless Charging The wireless charging module purchased from Adafruit requires a 9V source [5] (battery or external power supply) and outputs the same 9V on the load side. However, the Arduino runs on an internal 3.3V and can be driven off of a USB power of 5V. Furthermore, the LI battery used is 3.7V. The power electronics used to integrate the system included: 1) 9V battery/PS to Wireless Charging TX 2) Wireless Charging 9V TX to Wireless Charging 9V RX 3) Wireless Charging 9V RX to Buck Convertor Input 4) Buck Convertor output (5V) to USB Battery Input Module (5V) 5) USB Battery Input Module (5V) to LI Battery (3.7V) 6) LI Battery (3.7V) to USB Battery Output Module (5V) 7) USB Battery Output Module (5V) to Arduino USB Power Input (5V) 8) Arduino USB Power Input (5V) to Arduino Power Input (3.3V) The complexity of the power electronics and stepping down, then down, then up, then down requires more voltage conversions than necessary. However, for fast prototyping and with the available components, the complexity of the power electronics was necessary. Future implementations would include simplifying the conversions or at least localizing the conversions on board (rather than through external modules). D – Further Implementations The physical prototype only implements the three discussed main functionality, but serves as a spring board for future implementations. The two main future goals are system optimization and additional functionality. To optimize the system further, a Bluetooth based System on Chip (SOC) would be used such as the Broadcom BCM20737 . This SOC integrates a Bluetooth receiver on- chip, an ARM processor, and internal RAM [6]. While the RAM may not be sufficient to drive the current LCD, an external GPU/frame buffer could be used especially for a smaller display with optimized library code. A Bluetooth SOC would be the ideal solution because of the localized Bluetooth receiving and transmitting along with the decrease in overall system size. The BCM20737 also integrates battery management software capable of monitoring wireless charging [6] which further proves the worth of such a solution. The main additional functionality would fall under either software of hardware. Improved software functionality would include and improved user interface and additional applications. The user interface, like the Apple Smartwatch [4], would include a main menu for application selection. Then the smartwatch would display the selected applications interface and remain in the application until a user input return indication is made. Added applications could include a notepad (with capacitive touch), calendar, heart rate monitor (via hardware blood-pulse indicator), picture viewer, media player, and potentially an internet web browser (requiring WIFI compatibility). Additional hardware peripherals would include a microphone, speaker, gyro, accelerometer, WIFI chip, blood- pulse monitor (on rear of smartwatch), and vibrator (resonant actuator). The hardware peripherals would input to the main microcontroller and be accessed based on the current application. The current smartwatch prototype is simply a platform for many possible applications via sensors and displays. Almost any application (and more) run on a phone could be run on a smartwatch. However, the size constraint on a smartwatch is smaller than for a smart phone. The implementation of any of these applications using sensor inputs requires a cost-benefit business analysis. V – CONCLUSION In this experiment, a smartwatch prototype is created using inexpensive components in a short timeframe (less than 10 weeks). The prototype has three main components of LCD
6 display, Bluetooth communication, and wireless charging. These three components comprise a base requirement for a smartwatch with the intention that further improvements would be made before any final product. This proof of concept approach is used to show that with minimal time and money a smartwatch prototype can be created. The system is Arduino based so the software and hardware integration required less time to create than a more optimized system. The price of the system prototype is only $112.79 which is low considering the development boards are not optimized. This smartwatch prototype shows that a smartwatch can be implemented with little time and money, but the system is far from optimized and lacks certain functionality to compete with current on the market competitors. Overall, the barrier to entry to the smartwatch market is high because of the necessary optimization to compete with current products. So any final smartwatch product would require significantly more time, money, and expertise to accomplish.
7 Appendix References [1] Adafruit, “TFT Touch Shield” 2015. [Online] Available: http://www.adafruit.com/products/1651 [Accessed 14 May 2015]. [2] RedBearLab, “BLE Shield” 2015. [Online] Available: http://redbearlab.com/bleshield/ [Accessed: 16 May 2015]. [3] iFixit, “Apple Watch Teardown” 23 April, 2015. [Online] Available: https://www.ifixit.com/Teardown/Apple+Watch+Teardown/4 0655. [Accessed: 18 May 2015]. [4] iFixit, “Samsung Gear Live Teardown” 8 July 2014. [Online] Available: https://www.ifixit.com/Teardown/Samsung+Gear+Live+Teard own/27038#s66770 [Accessed: 18 May 2015]. [5] AdaFruit, “Inductive Charging Set” 2015. [Online] Available: http://www.adafruit.com/products/1407 [Accessed: 4 June 2015]. [6] Broadcom, “Low-Power Bluetooth 4.0 Single-Chip, BLE- Only SoC With Wireless Charging, NFC And RSA Security” 2015. [Online] Available: https://www.broadcom.com/products/wireless- connectivity/bluetooth/bcm20737 [Accessed: 4 June 2015].

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SmartWatch Prototype

  • 1. 1  Abstract—This experiment provides a working prototype of a smartwatch using inexpensive, commonly found components. The device consists of an LCD with touch-input capability for the user, a Bluetooth module to connect and communicate to the user’s mobile device, and a battery system that extends battery life with the ability to be charged wirelessly. Designing this system provides the authors with the opportunity to work with the integration of software and hardware, and create a device that combines the aforementioned technologies in a working, proof-of-concept computer system. Furthermore, the experiment provides the opportunity to research existing and future technologies that could be applied to this prototype to bring a product to market. I – INTRODUCTION URRENTLY, there exists a large barrier to entry in the smartwatch market. Proprietary technology and licensing deals with OEM’s make the design of a compact, complete smartwatch very difficult. Larger components are used in the design as smaller customized components would require prior knowledge of desired pinouts, communication protocols, and planned schematics. The larger breakout board components also provide freedom to interchange components and experiment with different hardware designs to find the optimal setup. Furthermore, the physical materials required to create a complete watch (leather/metal band, links, glass, etc.) are not readily purchased and assembled. For these reasons, we decided that the best approach to this problem would be development of a prototype device that combines a few core features commonly found in current smartwatch devices. In our prototype, we implemented three core features: a touch LCD, Bluetooth communications, and wireless charging for the battery. Upon completion of implementing these features, we have a working platform to build from if time permits. These features alone comprise a basic computer system: a controlling unit with a data path, a user interface, and a means of communicating to external systems. With core functionality in mind, the design process actually allowed us to perform a lot of research into both current and future technologies relevant to the various fields. The design carries out as a parallel process. With three team members and three core functions to implement, each member works individually on an assigned component, with periodic meetings to facilitate the integration of the three into the final system. The LCD is programmed and calibrated to perform the functions necessary of a watch face, the Bluetooth module is tested and set up to work with the microcontroller to be able to connect and communicate with a paired handheld device, and the battery requirements for the system are calculated and implemented. This project is valuable to us for multiple reasons. First and foremost, it is a project that is feasible to complete in about 7- 8 weeks of limited time, and provides us with an opportunity to learn about different engineering disciplines and combine them into a computer system, and it is always good practice to work with new and emerging technologies to keep engineering skills current. Much of modern engineering design requires analysis of datasheets, application notes, pieces of code, etc., which are important skills to have. Furthermore, the various components being implemented in the system come from different fields of electrical engineering. These fields include microcontroller programming, power electronics, Bluetooth communications, and mobile software development. Beyond that, our research led us to understand how our prototyped system could be improved in the future. II – COMPONENT DESIGN This design combines readily available components into a system that performs three core functions commonly found in commercial smartwatches. The primary system functions include capacitive touch input, displaying of time and date, and notifications of messages received on a paired Smart Phone device. The Bluetooth protocol is used to facilitate communications between the system and a mobile device. The design of the system is broken down into three distinct sections, including a display module, Bluetooth module, and wireless charging module as shown in Figure 1. Fig 1. Components included in prototype smart watch design. The controlling unit is an Arduino Uno microcontroller, and it interfaces seamlessly with the Bluetooth Low Energy Shield for Arduino and the Adafruit TFT Touch Shield for Arduino to form the core of the watch electronics. A battery system is used to power the Uno (which connects power and ground pins of all three boards, thus powering them all) to allow for Smart-Watch Prototype Charlie Aylward, David Ritter, and Eric Rule C
  • 2. 2 mobility. The Arduino UNO contains the MCU controlling the rest of the system by the means of SPI and I2C communication protocols. The Arduino UNO serves as an ideal prototyping main controller as it provides a large array of digital and analog pinouts which can behave as inputs and outputs. The Arduino UNO also provides the other system components with a power source. Fig 2. Arduino UNO with labeled headers for connections to added modules. A – LCD Module An Adafruit capacitive-touch LCD screen provides an interactive user interface. The screen is 2.8”, has a 240x320 resolution, and utilizes 16-bit color [1]. It communicates with the Uno via SPI, runs off 3.3V, and draws approximately 100mA when updating [1]. Most important are the basic watch functions of displaying the time and date. These are found at the top of the screen, and are updated as often as possible. The rest of the screen is reserved for displaying incoming notifications, sent via Bluetooth from a paired mobile device, usually a smartphone. When the watch receives a notification, the microcontroller processes it and displays the correct message to the user. This LCD is much larger than would be necessary on a real smartwatch, and as such, would be replaced in the future. Reducing the size of the screen would not only reduce the overall power consumption of the device, but also allow for greater utilization of the screen. Some choices that would be considered when choosing a screen technology such as LCD, AMOLED, or e-paper would be pixel density, various color/brightness/contrast attributes, and power consumption. The e-paper screen is dim and plain, but consumes an incredibly small amount of power, allowing for greater battery life. Deciding between LCD and LED technologies would be a matter of pricing and performance. B – Bluetooth Module The RedBearLab BLE board is connected to the Arduino Uno for the prototyping of this system, and it contains the necessary hardware to implement a fully functioning Bluetooth module. It supports multiple operating systems and Bluetooth protocols [2]. The purpose of this board is to allow Bluetooth communication pairing between the system and a user’s smartphone, to receive useful data from it. To complete this transaction of data, the Arduino software is configured to wait for data once a device is paired. When it receives a signal indicating some useful data has been transferred, it communicates to the Uno via ACI [2], which is a modified version of SPI, to have the data processed accordingly. For instance, if the user receives an email on their phone, the notification is sent over Bluetooth to the BLE board, and then to the Uno, where it processes the notification and displays the correct graphic on the LCD. To distinguish between different types of notifications received by the phone, some software must be installed. For this project, the Android OS by Google is supported (in the future, Apple’s iOS would also be supported) and an Android application must be installed to facilitate communication. The Android application requests to pair with the smart watch prototype, and sends the correct information to the BLE board once paired. Figure 3 illustrates the packet flow between the smart watch and a connected smart phone. This custom Android software is partially taken from some open source code found on the Internet, but has been modified for custom use. Fig 3. Bluetooth pack flow diagram between prototype smart watch (RX) and connected Android smart phone (TX) Currently, the prototyped system allows for email, text message, and call notifications. In the future, support for more functionality would be implemented on both ends, such as the ability of the watch to send various sensor data to the paired phone. Beyond that, the Android application would be substantially updated to provide a more comprehensive interface. C – Battery Module There are multiple constraints to consider when running an embedded system off battery power. The battery must have sufficient voltage to keep all circuits running simultaneously, and account for supply drops at times of high current draw at peak operation. The amp-hour capacity of the battery must be
  • 3. 3 more than enough to allow the device to run for a desired amount of time to prevent unwanted shut-offs due to power consumption. Furthermore, the battery must be physically sized to fit in the packaging that will be used to house the device. These constraints require analysis of device power consumption at different periods of operation: low-current draw “idle” state and peak current draw when the user is operating the device frequently. The manufacturer of the microcontroller used in this design recommend a battery voltage range of 7V to 12V. The lower bound of 7V is required to prevent the 5V traces from dropping too low and the upper bound prevents a voltage regulator from overheating and burning up. The first instinct is to jump to a 9V battery as the solution; however, the 9V cells generally have low capacity, and a lot of its energy will be burned off as heat being dropped to the lower voltages required by the controller. Since the battery must also be wirelessly rechargeable, this eliminates the choice of any standard store-bought cells. Herein lies the issue of barrier to entry: without integrating the necessary components into a single, compact system (as done in modern smartwatches), the battery will be much larger than it would actually need to be. Many smartwatches currently available use small, efficient rechargeable batteries: an iFixit teardown revealed that the Apple Watch uses a 3.8V, 205mAh lithium-ion battery [1], and the Samsung Gear Live uses a 3.8V, 300mAh lithium-ion battery [2]. These batteries are allowed to be so compact because the rest of the circuitry is optimized for the device and there are no unnecessary components. Our project, being a prototype, will not be nearly as efficient, and a 9V rechargeable cell will be sufficient as a proof-of concept. To charge the battery wirelessly, a simple set of inductive coils with charging circuitry was purchased from Adafruit, and are used to recharge the battery. This coil supplies 0.5A at max power transfer, and as such is not an ideal charging system. The Apple watch has a receiving coil and charging circuitry built into the device [1] and greatly simplifies the wireless charging of its battery. If this design were to be taken further and improved to the point of being viable as a consumer good, the battery system would change drastically. First of all, if the entire system was optimized to fit in a single housing, the battery could be reduced to a much smaller size, most likely one of the common 3.8V solutions. The wireless charging kit would be optimized to support one of the current standards being developed (PMA, WPC, A4WP) and reduce in size, while being able to supply a higher current such as 1A. III - SYSTEM ARCHITECTURE The Arduino UNO serves as the system’s main controller, keeping track of connected devices and running the code, which provides the system with functionality. The Arduino UNO was a good fit for our needs as it offers multiple communication protocols and an abundance of digital and analog IO pins for adding devices. Along with the hardware benefits of the Arduino UNO, there are easy to use code libraries available for software development. Many attachable devices have manufacturer-developed API meant to interface the device with Arduino systems. Both the RedBearLab BLE Shield and the TFT LCD display offer example code and libraries for the Arduino UNO simplifying the software development process. Fig 4. System Component Setup showing connection methods for RedBearLab BLE Shield and TFT LCD Screen. The primary functionality for the prototype device includes time display, Bluetooth notifications, and wireless battery charging. Both time keeping and Bluetooth communication rely heavily on the software for correct operation. Bluetooth notifications specifically require a separate device such as a smart phone for the intended functionality. The goal of this project is to pair the prototype with an Android smart phone. The Android Operating System was chosen as it allows open source development. Communication with a smart phone requires that the phone have software enabling it to function properly. Smart phone applications serve this purpose and can also grab system information from the phone, such as notifications. With an application on the smart phone, the smart watch prototype system can successfully receive notifications from the connected smart phone via Bluetooth. Figure 5 shows the system block diagram with the smart watch modules and the Bluetooth-connected Android smartphone. Fig 5. Block diagram of system design and system interfaced with Bluetooth compatible Android smartphone. The software development process involved two main parts.
  • 4. 4 First, the Arduino microcontroller required the necessary code to keep track of time, communicate with the Bluetooth shield, and communicate with the touch screen display. Second, an Android application able to pull notifications from an Android smart phone and establish a connection with the Bluetooth shield on the prototype needed to be developed. The time keeping software utilizes the Arduino Time library. More specifically, the function “millis()” is an Arduino method that keeps track of the milliseconds after the initialization of the program code once loaded onto the Arduino. By setting the initial time in the code and using the Time functionality mentioned, the Arduino is able to serve as a clock. Using the TFT LCD display, the time can be output to the screen in a readable format showing the current time (up to seconds) and date. Software needed for communication with the RedBearLab Bluetooth shield and the Adafruit TFT LCD display was available in libraries from the respective manufacturers. This made the initial task of establishing connections simple and left only the programming toward our specific application. The Bluetooth shield did not require much initialization code beyond setting the broadcast name. With the name established, a single function calls begins the operation of the Bluetooth shield. Once in “operating mode”, another function call polls for devices requesting to be paired. Once paired, a separate function checks for data being sent along the connection toward the BLE shield. In this system, the Bluetooth transmission is unidirectional from the phone to the BLE shield. This setup is appropriate, as the prototype device only needs to receive Bluetooth information from the smart phone. If a notification is received over Bluetooth by the BLE shield, the microcontroller draws an indication graphic to the display. The interfacing to the TFT LCD display also requires minimal setup. The initialization involves drawing a background to the screen and creating the time display. After initialization, the display shows notification graphics and updates the time when triggered. Figure 6 shows the system’s software workflow. Fig 6. Software flowchart for the Arduino UNO microcontroller interfaced with the Bluetooth shield and TFT LCD display. IV – DISCUSSION OF RESULTS The working smartwatch prototype implements the three discussed functionality of LCD display, Bluetooth communication, and wireless charging for only $112.79 (see Appendix for BOM). While the user interface is primitive in design and functionality, the smartwatch displays the time and integrates Capacitive Touch functionality for changing the color of the Bluetooth notification icon. The Bluetooth communication is demonstrated with email notifications displayed to the LCD screen from an external Android phone (via a user created Android application). The wireless charging is integrated via a 3.3V LI battery that drives the entire Arduino based smartwatch system. Overall, the system behaves as discussed in the System Architecture section, and integrates the three components. A few of the issues encountered during implementation of the prototype follow.
  • 5. 5 A – Challenges with the LCD The sample code found on the Ardiuno website for the Capacitive Touch LCD display requires explicitly writing to each pixel or group of pixels on the LCD. Therefore each time the time display is updated, the previous time (or anything on the display) must be written over to erase the previous display. Because the sample code is not optimized, the writing and rewriting of something even as small as the time bar must be locally erased. The update or “loop” cycle cannot update fast enough for the Bluetooth and erasing the entire display every cycle. This bug was fixed by locally erasing the changes to the display rather than continuously refreshing the entire display buffer (erasing the entire display and rewriting to all the pixels). B – Challenges with Bluetooth The Arduino Bluetooth sample code found online utilized an Android application for communication with the Arduino BLE shield. However, the application originally required user input to change a set of LEDs. This code was modified to first display a notification and then access the Android notification outputs to trigger a display sequence (i.e. to display an icon on the LCD). The internal Android email notification flag required modifying the Android application to accept email notifications. This required both access permission on the Android operating system and integrating the notification to trigger the LCD icon display via Bluetooth. C – Challenges with Wireless Charging The wireless charging module purchased from Adafruit requires a 9V source [5] (battery or external power supply) and outputs the same 9V on the load side. However, the Arduino runs on an internal 3.3V and can be driven off of a USB power of 5V. Furthermore, the LI battery used is 3.7V. The power electronics used to integrate the system included: 1) 9V battery/PS to Wireless Charging TX 2) Wireless Charging 9V TX to Wireless Charging 9V RX 3) Wireless Charging 9V RX to Buck Convertor Input 4) Buck Convertor output (5V) to USB Battery Input Module (5V) 5) USB Battery Input Module (5V) to LI Battery (3.7V) 6) LI Battery (3.7V) to USB Battery Output Module (5V) 7) USB Battery Output Module (5V) to Arduino USB Power Input (5V) 8) Arduino USB Power Input (5V) to Arduino Power Input (3.3V) The complexity of the power electronics and stepping down, then down, then up, then down requires more voltage conversions than necessary. However, for fast prototyping and with the available components, the complexity of the power electronics was necessary. Future implementations would include simplifying the conversions or at least localizing the conversions on board (rather than through external modules). D – Further Implementations The physical prototype only implements the three discussed main functionality, but serves as a spring board for future implementations. The two main future goals are system optimization and additional functionality. To optimize the system further, a Bluetooth based System on Chip (SOC) would be used such as the Broadcom BCM20737 . This SOC integrates a Bluetooth receiver on- chip, an ARM processor, and internal RAM [6]. While the RAM may not be sufficient to drive the current LCD, an external GPU/frame buffer could be used especially for a smaller display with optimized library code. A Bluetooth SOC would be the ideal solution because of the localized Bluetooth receiving and transmitting along with the decrease in overall system size. The BCM20737 also integrates battery management software capable of monitoring wireless charging [6] which further proves the worth of such a solution. The main additional functionality would fall under either software of hardware. Improved software functionality would include and improved user interface and additional applications. The user interface, like the Apple Smartwatch [4], would include a main menu for application selection. Then the smartwatch would display the selected applications interface and remain in the application until a user input return indication is made. Added applications could include a notepad (with capacitive touch), calendar, heart rate monitor (via hardware blood-pulse indicator), picture viewer, media player, and potentially an internet web browser (requiring WIFI compatibility). Additional hardware peripherals would include a microphone, speaker, gyro, accelerometer, WIFI chip, blood- pulse monitor (on rear of smartwatch), and vibrator (resonant actuator). The hardware peripherals would input to the main microcontroller and be accessed based on the current application. The current smartwatch prototype is simply a platform for many possible applications via sensors and displays. Almost any application (and more) run on a phone could be run on a smartwatch. However, the size constraint on a smartwatch is smaller than for a smart phone. The implementation of any of these applications using sensor inputs requires a cost-benefit business analysis. V – CONCLUSION In this experiment, a smartwatch prototype is created using inexpensive components in a short timeframe (less than 10 weeks). The prototype has three main components of LCD
  • 6. 6 display, Bluetooth communication, and wireless charging. These three components comprise a base requirement for a smartwatch with the intention that further improvements would be made before any final product. This proof of concept approach is used to show that with minimal time and money a smartwatch prototype can be created. The system is Arduino based so the software and hardware integration required less time to create than a more optimized system. The price of the system prototype is only $112.79 which is low considering the development boards are not optimized. This smartwatch prototype shows that a smartwatch can be implemented with little time and money, but the system is far from optimized and lacks certain functionality to compete with current on the market competitors. Overall, the barrier to entry to the smartwatch market is high because of the necessary optimization to compete with current products. So any final smartwatch product would require significantly more time, money, and expertise to accomplish.
  • 7. 7 Appendix References [1] Adafruit, “TFT Touch Shield” 2015. [Online] Available: http://www.adafruit.com/products/1651 [Accessed 14 May 2015]. [2] RedBearLab, “BLE Shield” 2015. [Online] Available: http://redbearlab.com/bleshield/ [Accessed: 16 May 2015]. [3] iFixit, “Apple Watch Teardown” 23 April, 2015. [Online] Available: https://www.ifixit.com/Teardown/Apple+Watch+Teardown/4 0655. [Accessed: 18 May 2015]. [4] iFixit, “Samsung Gear Live Teardown” 8 July 2014. [Online] Available: https://www.ifixit.com/Teardown/Samsung+Gear+Live+Teard own/27038#s66770 [Accessed: 18 May 2015]. [5] AdaFruit, “Inductive Charging Set” 2015. [Online] Available: http://www.adafruit.com/products/1407 [Accessed: 4 June 2015]. [6] Broadcom, “Low-Power Bluetooth 4.0 Single-Chip, BLE- Only SoC With Wireless Charging, NFC And RSA Security” 2015. [Online] Available: https://www.broadcom.com/products/wireless- connectivity/bluetooth/bcm20737 [Accessed: 4 June 2015].