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FITtape
Fitness Information Tracking Tape Measure with Bluetooth Data Syncing
Alex Chuang
Table of Contents
Introduction .................................................................................................................................................. 2
Microcontroller ............................................................................................................................................. 2
System Power ............................................................................................................................................... 2
Battery Pack and Charging ........................................................................................................................ 2
Voltage Output Control............................................................................................................................. 3
Encoder ......................................................................................................................................................... 3
Bluetooth ...................................................................................................................................................... 3
User Interface ............................................................................................................................................... 3
Display ....................................................................................................................................................... 3
Capacitive Touch Interface ....................................................................................................................... 3
Pushbutton Switch .................................................................................................................................... 4
Servo Control ............................................................................................................................................ 4
Bill of Materials ............................................................................................................................................. 5
FITt a p e | 2
Introduction
FITtape is a fitness monitoring system that allows the user to easily take body measurements and store
them for long-term tracking. It achieves this through the use of a powerful, yet efficient, ARM M0+ core
controlling several levels of operation. The FITtape takes length measurement by using a tape on a
retracting reel. The system records these measurements using a rotary quadrature encoder and stores
them to onboard memory until system is synced to a Bluetooth or USB enabled device. The device also
can operate independently of a Bluetooth/USB host device. The FITtape has a super low powered LCD
and simple user interface.
Microcontroller
The MCU in the FITtape is a Freescale Kinetis L MLK25Z128VFM4 ARM M0+ core on a QFN-32 SMD 32pin surface mount package. The microcontroller will be running off its internal clock because the time
scale between measurements is 3 to 4 days. It will be able to resync its calendar whenever it connects
via Bluetooth or USB. In order to communicate with other modules, it uses the SPI1 ports and chip
selects between SPI devices. The two devices running off SPI are the LCD screen and the Bluetooth
module. All the other pins are GPIO pins that read input of the encoder, user interface, or output control
to the servo system. The FITtape uses 30 of the available 32 pins on the Kinetis chip.
The Kinetis L line was chosen for its low power characteristics. When the device isn’t being used after a
short period of time, it will go into sleep mode. It wakes on the sleep/power button. The decision to go
with the KL25Z128 was due to the memory requirement of the graphic user interface.
System Power
Battery Pack and Charging
The FITtape is a battery powered device running on a Lithium Polymer single cell 500mAh battery. The
battery pack comes with its own protection circuit that protects it from overcharge and overdischarge.
The maximum charging rate is 150mAh. In order to charge the device, the user will be able to use any
standard USB charger. The charge controller is a MCP73831T-2ACI/OT regulates the charge current to
125mAh to stay a safe margin away from the maximum charge rate.
The charging circuit also uses a load balancing chip that consists of a p-channel MOSFET, Q1-1, and a
zener diode, Q1-2. This allows the 5V of the USB bus to power the device while the battery is charging
without interfering with the operation of the charge controller.
FITt a p e | 3
Voltage Output Control
The FITtape runs on both 3.3V and 5V. In order to achieve this, the FITtape uses two switching
regulators. The TPS63001DRCR is a Texas Instruments 3.3V, 1.8A switching Buck/Boost converter with
an input range between 1.8 and 5.5V. This powers the MCU, encoder, LCD, and Bluetooth modules. The
input range allows for the voltage range of the battery and the voltage input of any USB chrager.
The TPS61030PWPR is a 5V boost converter that powers the servo for the measuring tape retracting
system. This device has an enable that can disconnect the load from power when not in operation. This
feature is ideal for power saving and allowing the use of the small 500mAh battery.
Both of these devices were designed using the recommended specifications given by TI.
Encoder
The AS5035-ASST is a magnetic encoder integrated circuit that outputs a quadrature AB/Index set of
pulses. The device operates at TTL and CMOS levels depending on the power driving the device. Since it
is being driven at 3.3V, it matches the MCU voltages for GPIO input pulses at 3.3V. The AS5035-ASST has
an output resolution of 64 pulses per revolution. This allows for an overall tape measure resolution of
2mm increments, making it the most accurate digital fitness tape measure in the industry. The encoder
has a consumption of 500mAh. In order to preventing excessive drain on the battery, the encoder is
enabled using a P-channel mosfet in order to reduce power consumption.
Bluetooth
The 450-0103C Bluetooth module is a one part solution that is FCC compliant. This allows the FITtape to
be within compliance without any extra testing. The module communicates with the MCU via the SPI1
channel on port D. The device is powered by 3.3V and has a low power consumption because of the
device is focused towards low energy. The Bluetooth power pins have two choke circuits in order to
prevent over current.
User Interface
Display
The LCD display is a SHARP LS013B4DN04 transreflective display. It is a super low power display with a 1bit latch for every pixel. This allows the LCD to hold its state without always refreshing. The display is a
write-only device on the SPI1 channel and doesn’t have controller so this requires the MCU to buffer the
display data. At 96x96 pixels, this requires 1,152 bytes of memory on the MCU be dedicated to graphics
output.
The display is enabled by pin 28 on the MCU.
Capacitive Touch Interface
The capacitive touch interface will be built into the body of the device as a glass lay-over of the screen
with slider beneath it. This is done using copper electrodes behind the glass to pick up the change in
capacitance when a person slides or taps the slider. This inputs to the touch sense interface on the
Kinteis L chip.
FITt a p e | 4
Pushbutton Switch
The pushbutton switch ties to a pin that the Kinetis chip reads to wake from sleep state. When awake,
the pushbutton will sleep the device after being held for 1 second.
Servo Control
The servo is powered by the 5V boost converter and its power draw is controlled by the built in enable
of the converter. The KL25Z MCU will output a PWM signal on PTA4 to control the location of the servo.
The servo draws .5A so limiting the operation of the servo is of paramount importance. This is achieved
by only operating the servo when it needs to be moved, which is only long enough for the servo arm to
move 5 degrees.
FITt a p e | 5
Bill of Materials
Item # Qty
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Description
Battery - 3.7v 500mAh LiPo single cell
IC- MCP73831T-2ACI/OT
IC - 450-0103C
IC- TPS63001DRCR
IC- TPS61030PWPR
LCD - LS013B4DN04
IC- AS5035-ASST
IC -MLK25Z128VFM4
MOSFET - NTHD3101FT1G
MOSFET - Si2347DS-T1-GE3
Ferrite Bead - BKP2125HS331-T, 330Ω
RGB LED - CLV1L-FKB-CHMMQEHBB7673673
SERVO - T010050, 5V
SWITCH - EVQ-Q2B03W, push button tactile
CONNECTOR - XF2L-1025-1A
CONNECTOR - S2B-PH-SM4-TB(LF)(SN)
CONNECTOR - 10118193-0001LF Micro USB B
CONEECTOR - 2x5 pin header
RES - 100kΩ, 1%, 1/8W, 0805 SMD
RES - 300kΩ, 1%, 1/8W, 0805 SMD
RES - 33Ω, 1%, 1/8W, 0805 SMD
RES - 8kΩ, 1%, 1/8W, 0805 SMD
RES - 10kΩ, 1%, 1/8W, 0805 SMD
RES - 220Ω, 1%, 1/8W, 0805 SMD
INDUCTOR - 2.2uH, 10%, 0805 SMD
INDUCTOR - 5.6nH, 10%, 0805 SMD
INDUCTOR - 6.8uH, 10%, 0805 SMD
CAP - 10uF, 20%, Radial,Can-SMD
CAP - 100pF, 20%, Radial,Can-SMD
CAP - 220uF, 20%, Radial,Can-SMD
CAP - 2.2uF, 20%, Radial,Can-SMD
CAP - 1uF, 20%, Radial,Can-SMD
CAP - .1uF, 20%, Radial,Can-SMD
CAP - 100nF, 20%, Radial,Can-SMD
Designator
B1
U1
U2
U3
U4
U5
U6
U7
Q1
Q2
FERR_BD1
LED1
M1
SW1
CN4
CN1 CN3
CN2
CN5
R1
R2 R8
R3 R5
R4
R6 R7
R9 R10 R11
L1
L2 L3
L4
C1 C2 C4 C5 C9
C3 C6
C7
C8 C16
C10 C11 C13
C12 C14
C15