FITtape Digital Fitness Tape Measure with Data Syncing Alex Chuang Table of Contents Introduction .................................................................................................................................................. 3 Product Overview ......................................................................................................................................... 3 Dimension Specifications .......................................................................................................................... 3 Features .................................................................................................................................................... 4 Hardware Systems ........................................................................................................................................ 4 Microcontroller ......................................................................................................................................... 4 Microcontroller Resources Used............................................................................................................... 5 Electromechanical Systems....................................................................................................................... 5 Magnetic Tape Latch ................................................................................................................................. 5 Measurement Encoder ............................................................................................................................. 6 Display ....................................................................................................................................................... 6 Human Machine Interface ........................................................................................................................ 6 USB Interface ............................................................................................................................................ 6 Bluetooth Interface ................................................................................................................................... 6 Power Supply ............................................................................................................................................ 6 Charging Unit ............................................................................................................................................ 6 Software System ........................................................................................................................................... 7 Software Development ............................................................................................................................. 7 Kernel ........................................................................................................................................................ 7 User Interface ........................................................................................................................................... 7 Encoder Algorithms................................................................................................................................... 8 Modules .................................................................................................................................................... 9 Sustainability ................................................................................................................................................. 9 Standards ...................................................................................................................................................... 9 Bluetooth Low Energy v4.0 ....................................................................................................................... 9 USB v2.0 .................................................................................................................................................... 9 ROHS Compliance ..................................................................................................................................... 9 Development Plan......................................................................................................................................... 9 Development Tasks ................................................................................................................................... 9 Development Platform ........................................................................................................................... 10 Demonstration Prototype ....................................................................................................................... 10 Specifications .............................................................................................................................................. 10 Included components ............................................................................................................................. 10 Sizing ....................................................................................................................................................... 10 Measurement Capability......................................................................................................................... 10 Wireless Sync .......................................................................................................................................... 11 Battery Specification ............................................................................................................................... 11 Power dissipation.................................................................................................................................... 11 Preliminary Parts List .................................................................................................................................. 11 2 Introduction The FITtape is part of a fitness tracking system that allows the user to easily take body measurements by digitally measuring and tracking the measurements of the body parts the user wants to track. This system includes a handheld measurement unit and an application based system used for syncing data. The user will be able to select the desired body measurement from the handheld unit’s GUI and then record the measurement using the automatically controlled tape measure. The FITtape features Bluetooth capability which can be implemented by interested developers to use the tracking information for fitness applications. Product Overview The FITtape is part of a system that consists of a hardware and software approach to fitness metrics. The FITtape tape product is the hardware interface for users to take measurements and temporarily store data for performance metrics. Dimension Specifications The FITtape is a handheld measurement unit and charging adapter. The FITtape has a maximum dimension of 3.5”x2.5”x1.25”. The user interface consists of a square LCD screen with a viewing area of approximately 1.5” diagonal and a capacitive touch strip which also serves as a button. There will also be a micro USB port on the device for charging and wired data syncing. The tape is 60” long since the intended use is not for height measurements. The tape will feature a strong magnet at the end that latches back to the measurement unit body to create a loop for easy one handed measurements. The charging unit is an OEM USB wall charger, the dimensions will not exceed 2” x 2” x 3”. Figure 1: FITtape product drawing #1, no capacitive touch strip visual test 3 Features Prioritized by development importance 1. Electronically controlled measurement control system: The most basic operation of the FITtape is the electromechanical system that simplifies the measurement process into a one click process. 2. Bluetooth/USB device data syncing: The key feature that sets the FITtape apart is device connectivity. By having data syncing capability, the end user will have access to long term data tracking and performance metrics. 3. Intuitive user interface on measurement unit: In order to make FITtape competitive, it has to provide a streamlined and enjoyable user interface. 4. Rechargeable battery system: A rechargeable system provides convenience for the user but in the event of development taking too long, an alkaline battery system will be used. Hardware Systems The hardware of the FITtape systems is all contained within the handheld measurement unit. This includes a microcontroller, Bluetooth wireless transceiver, electromechanical components for automated measurement control, and user interface components such as a screen and buttons. Figure 2: Block Diagram of the FITtape electronics Microcontroller The FITtape is designed to be controlled by a Freescale Kinetis KL25Z128VFM4 MCU. The KL25Z128VFM4 is 48MHz, 32 pin chip with 128 kB flash and 16kB SRAM. It comes with 23 GPIO pins, 12 of which have interrupts. The RTC of the KL24Z128VFM4 will be used for logging the measurements according to 4 calendar and time of day. The chip also features capacitive touch capability which will be implemented in the form of a capacitive touch strip. The unit cost for 10k units is $1.74. The prototyping platform will be the Freescale Freedom platform model FRDM-KL25Z. The KL25Z features a KL25Z128VLK4 sharing the same clock speed and features. The memory is 128kB flash and 16kB SRAM. The chip also has nearly 3 times the GPIO pins at 66 pins, 23 which have interrupts. The prototyping platform has a total of 84 pins, which needs to be taken into account during the prototyping stage to prevent using pins that are not available on the final product. Microcontroller Resources Used The components of the FITtape will use approximately 16 data lines: Component Data Lines Used Quadrature Rotary Encoder 2 Solenoid power FET 1 Capacitive Touch Slider 2 Switch 1 LCD Screen 5 Bluetooth Module 5 Data Type GPIO GPIO GPIO GPIO SPI SPI Electromechanical Systems The measuring unit contains an electromechanical system for controlling the measuring tape that consists of a solenoid, ratchet and pawl gears, a constant force spring, and the measuring tape. The microcontroller sends a voltage out to the gate of a MOSFET which is driving the solenoid to unlock the pawl gear. This allows the measuring tape to retract. The pawl is held in place using a light spring and the solenoid is a push solenoid which levers the pawl behind the pivot point. The tape is loaded with a light constant force spring and is 60 inches long. Magnetic Tape Latch The tape measure has a magnetic latch at the end that locks back to the opening of the tape to create a loop for easy one handed usage. The tape latch will most likely use small rare earth magnets in order to have a usable holding force. Figure 3: Magnetic latching mechanism, rare earth magnets latch into body. 5 Measurement Encoder A rotary encoder will be mechanically coupled to the tape near the opening of the tape. This encoder is a 64 pulse per revolution optical encoder with a minimum lifecycle of 1 million full revolutions. This encoder was chosen due to its higher operational life compared to similar products. The quadrature behavior of the encoder means that it takes two data lines to send the pulses to differentiate direction. Display The display is a 1.5” LCD display with a minimum resolution of 64x64 pixels. It will communicate via SPI and will take 5 pins. The display will allow the user to select from 8 to 10 different icons representing body parts along with an icon representing confirmation of measurement. Human Machine Interface The user interface is made up of a capacitive click-pad. This is a combination of a touchpad and switch which is common to many devices such as MP3 players and laptops. The Kinetis KL25 series supports TSI which is Freescale’s capacitive touch interface. The touchpad will be in the shape of a horizontal strip and will behave as a slider. Once the user has initiated a measurement, no inputs will be read until the measurement is done. The user will then have the option to keep or discard the measurement. USB Interface The KL25Z64VFM4 features a USB controller with on-chip full-speed and low-speed transceivers. The USB module will be able to communicate with an application as a human machine interface in order to isolate the data from accidental manipulation. The KL25Z is configured for full-speed USB and the FITtape will also be configured to full-speed USB because the 5V USB line will charge the lithium polymer battery. Bluetooth Interface The Bluetooth transceiver on the FITtape unit will use Bluetooth Low Energy, v4.0 standard. The transceiver chip has an operating range from 1.8V to 3.6V and has a current draw of 16mA receiving or transmitting. The desired chip is a surface mount chip with a 6mm x 6mm footprint. The chip uses UART or SPI communication, I have chosen SPI in order to lower the number of pins used. The unit cost is between $1.50 and $5.80 depending on volume. Power Supply The FITtape will use a 3.7V rechargeable lithium polymer battery along with a boost converter to reach the requisite voltage to drive the solenoid and encoder. In order to have stable operation, the system will also have a voltage regulator to keep the power output at 3.6V during usage. In order to safely charge the device on a 5V USB power line, it is necessary to have a charge protection circuit. Charging Unit The charging unit will be an OEM USB wall charger with an input of 110V to 240V and output of 5V, 2A providing a 10W total power output. Because this OEM device is UL certified, there are no needs to worry about power concerns for safety. 6 Software System The software includes the development of the firmware for the measurement device and a standard data format for the measurements. Software Development The FITtape measurement module will be programmed in the Freescale Codewarrior environment using ANSI C as the programming language. Kernel The FITtape will run on a real time kernel, checking between the machine interfaces and the human interface. Upon user input to start measurement, the measurement operation will have top priority without the ability to be interrupted except for low battery shutdown to save the unit from losing data. User Interface The screen on the FITtape measurement unit is a monochrome negative LCD with RGB backlight. The capacitive strip selects a measurement type and clicking the touch strip will initiate the measurement process. The device can change measurements between centimeters and inches via the settings selection. The graphics of the user interface will be converted to data by using MATLAB to take the predesigned icons and turning them into data arrays. This data will be loaded onto the SRAM including alphanumeric font data. Figure 4: Measurement Device user interface screenshot simulation version 1 Figure 4: Icons representing body mesurements Figure 5: Screen showing icon in input mode 7 Figure 6: Screen showing measurement mode Figure 6: User interface flow diagram The user interface goes through two states, measurement and input. The input states can transfer between each other by scrolling on the touch strip. In order to transition to measurement, the user has to click to select a measurement. Once the measurement is complete, confirm will return to input screen. Setting has a similar input fashion where select will move into the select menu and after settings are changed, confirm will return to the input menu. Encoder Algorithms The encoder wheel is designed to be .64” in diameter. In order to get the increments, the circumference is calculated to be .64” * π. This length is divided into 64 segments. This allows for a resolution of .01” as intended. The measuring unit will measure natively in inches and convert to centimeters using this conversion formula: πΏππ = πΏππ ∗ 2.54 The unit will store the inch measurements and only convert to centimeters as needed. 8 Modules The FITtape will utilize several self-written modules along with a few standard modules. The standard modules includes the Freescale TSS capacitive touch sense software that is included with the Freescale Kinetis KL25 microprocessors. The Bluetooth transceiver and LCD screen with both also have their own separate modules. The electromechanical systems will also run in their own module to run as an interrupt because the measurement a critical process. Sustainability Since the FITtape does not use replaceable batteries, the consumer will have to properly dispose of the lithium polymer battery along with recycle the unit much like a modern cellular phone. The parts on the measurement unit use enough electronics components that sending the unit in for recycling will be beneficial to the environment and be more cost effective than destroying it. Standards The FITtape has to adhere to several standards for consumer usage. These include Bluetooth v4.0, USB 2.0, and RoHS. Bluetooth Low Energy v4.0 In order for the FITtape to meet compliance for Bluetooth communication, we have to follow Bluetooth Core Specification v4.0. USB v2.0 The FITtape makes use of the USB controller on chip to communicate with host devices. This communication has to follow the USB 2.0 specification. The device will behave as an HMI in order to preserve the data on the device and prevent the user from overwriting any important data on the FITtape. ROHS Compliance All ordered components have been RoHS compliant. Development Plan Development Tasks The development cycle of the FITtape is very short with only enough time to build a couple prototypes. In developing the FITtape, it is important that the first prototype comes out as rapidly as possible in order to test the functions and long term durability of the product. The development plan occurs mostly in the winter months. The order of project scheduling is as follows: Weeks Task WINTER 1-3 Completing a working prototype for the electromechanical system WINTER 4-5 Building working prototype for the encoder and MCU ADC 9 WINTER 6 Combine electromechanical control with encoder system for full measurement. Implement click wheel functionality. WINTER 7-10 Setting up screen functionality: develop fonts, icons, port to arrays, get LCD to display WINTER 11-12 Interface Bluetooth module with device. Begin wireless transmission development SPRING 1-4 Develop app to take Bluetooth communication, debug data transmission system SPRING 4 Hardware Design Review SPRING 5 Software Design Review SPRING 4,5 Test systems SPRING 6-8 PCB design, simplification of systems SPRING 8-11 Final testing, video shooting, project presentation design. The delivery time critical parts are the initial parts for each system. The electromechanical, HMI, and Bluetooth interfaces can be developed concurrently. The development tasks laid out in the schedule use a logical progression of what components are most vital to the function of the FITtape. Development Platform The development platform is the Freescale Freedom KL25Z development board and the Freescale Codewarrior environment for microcontrollers. This development platform supports all KL series chips as long as the program doesn’t run over memory requirements. Since the device is a handheld, the development requirements will be fairly light as the FITtape is a microcontroller based device. Demonstration Prototype The demonstration prototype will be the 2nd or 3rd iteration of the FITtape. This iteration will have a PCB and a monocoque ABS plastic chassis. The measurement unit PCB will use SMD components where possible to minimize footprint. The display will use an android device showing the tracking app along with having a live prototype of the FITtape. Along with these devices, the display will include an informational poster and 2 minute promotional video showing the function and benefits of the device. Specifications Included components ο· ο· ο· FITtape measurement tracker Charging cable Charging unit Sizing Length Width Height Tape Length Screen Size 3.5 inches (88.9 mm) 2.5 inches (63.5 mm) 1.5 inches (38.1 mm) 60 inches (1524 mm) 1.5 inches (63.5 mm) Measurement Capability FITtape will keep measurement data for each measurement up to 20 previous measurements. The measurements are in inches with an accuracy down to .01 inches. 10 Wireless Sync FITtape has a close range wireless sync of a maximum range of 15 feet. Battery Specification Battery Battery life Battery Type Charging Type 2200mAh 10 days (nominal use of once every three days) Lithium Polymer USB 5V or 5V wall charger Power dissipation KL25 Solenoid LCD Boost Converter Active Power Dissipation 70mA worst case 133mA nominal 100% duty, 2.3A worst case 3mA 35µA Sleep Power Dissipation 10µA worst case - Average use 2 times a week 10 times a usage - 15 minutes active 15 minutes active The total power dissipation is ultimately up to the end user. Based on the recommended intervals for taking measurements, the user should be taking measurement a maximum of once every three to four days. From this type of usage, with the solenoid being cycled 10 times per usage the total worst case would completely drain the battery if the solenoid was stuck on 100% of the usage time. For nominal usage, there cycle time is no longer than 1.5 seconds and the current draw is drastically lower, allowing for three uses before requiring a recharge. This gives a standard battery life of 9 to 12 days. Preliminary Parts List Component Freescale KL25Z128VFM4 LCD module Boost Converter Bluetooth Module MOSFET Rotary Encoder Resistors Capacitors Battery Management Module Battery Touchstrip components Mechanical components Rare Earth Magnets USB components Case Material TOTAL Lead Time n/a 1 month 2 weeks 2 weeks 2 weeks 2 weeks 2 weeks 2 weeks - Cost $1.74 $3.71 $1.37 $2.47 $0.44 $14.43 $2.00 $4.00 $2.00 $9.99 $1.00 $5.00 $2.50 $0.79 $5.00 $51.94 The cost of unit is mostly the rotary encoder and battery. If sourced properly, the total cost of the FITtape can be driven down 20% 11