Transcript Document

Lapview – The Swimmer’s Watch
Department of Electrical and
Systems Engineering
ABSTRACT
Keeping track of laps while swimming can be a difficult task. The
idea for the Lapview watch was conceived with the intent of
creating a simple device that could automatically count laps for a
swimmer, with absolutely no manual intervention . The goal was to
create a simple (and small) watch – dongle system which could
communicate wirelessly. This would allow portability, convenience,
and user friendliness, making Lapview a must have for every
swimmer.
System Overview
A number of technological solutions were considered and tested, including Bluetooth, RF (Radio
Frequency), and UltraSonic Ranging. Due to the various constraints (battery life, range, and most
importantly application under water), eventually a magnetic communication route was chosen.
Near-field magnetic communication uses a non-propagating quasi-static magnetic field to communicate
between a transmitter and receiver. The transmitter generates a magnetic field via a current flowing
through a coil, and the field can be detected by a magnetic field sensor. The one issue with magnetic
field sensors is that they are highly sensitive to the orientation of the magnetic field, which could alter
the field strength at different positions in the pool. In order to conquer this issue, the Lapview system
integrates two coils, perpendicular to each other, and pulsing 90° out of phase with each other.
ADVISOR
Transmitter Software: A simple program runs in an infinite loop and sends a 5V signal through a
port to each inductor at intervals of 200ms. The signals are sent to each inductor 90° out of
phase, while the inductors are also physically perpendicular to each other.
Watch Software: The software on the watch needs to interface the Polar Receiver Module, 3
push buttons, and an OLED display to the microcontroller. When the watch is in Lap Mode, it is
constantly polling the Polar Receiver Module, searching for a magnetic field. When a signal is
detected, the lap count is incremented. The algorithm is also able to ensure that multiple signals
detected without first being out of range for a sufficient time delay do not increment the lap
count.
In Lap Recall mode, the watch is able to scroll through the previous 99 laps that have been
stored in memory. Using 2 push buttons, it is possible to scroll up or scroll down the list.
PRESENTERS
Hardware Components
The Polar Receiver Module RM3V90D is a low voltage receiver
module that is able to detect 5 KHz magnetic pulses. The output
is a simple 0V for logic zero and Vcc for logic 1. The output pulse
length is 10ms.
PRESENTERS
Suman Addya EE ‘08
Vasudev Kulkarni CTE ‘08
GROUP 11
Two Microcontrollers were programmed for use in the Lapview system. The first controls the
watch, and the second is used to pulse the transmitter circuit at 5 KHz. The microcontrollers
were first loaded with the Arduino Bootloader, which would allow programming in the open
source Arduino Platform, which is based on C/ C++. The Arduino language supports all standard
C constructs and some C++ features. Most importantly however, it makes programming
microcontrollers without any external hardware extremely simple.
Lap times are calculated using an oscillator which is interfaced to the microcontroller’s internal
clock function. The ATMEGA168V along with a 16 KHz oscillator was able to provide accurate
timing in the millisecond range.
In order to create a device that could work in air as well as under
water, magnetic communication was chosen as the technological
direction. A dongle at the edge of the pool would transmit
magnetic pulses for a short range of zero to five feet. A magnetic
field sensor in the watch would detect the field every time the
swimmer came within range, and communicate this information to
the processor in the watch, allowing lap number and lap time to be
calculated and displayed.
The final implementation of the device implements an OLED
display that incorporates lap count , lap time, and review of up to
99 previous laps. Three buttons on the side of the watch allow
selection of modes, start/ stop, lap recall, and lap resetting. The
hope is that the extremely affordable Lapview watch will become
as standard a swimming accessory as goggles and trunks
Software Overview
The biggest challenge for the Lapview system was to create a transmitter that was able to create a 5
foot range (as opposed to the fairly standard 3 foot range seen in near-field magnetic communication).
The final circuit made use of a large inductor made from a ferrite core and wound with approximately
500 turns. A MOSFET Driver was able to take 9V from a battery and amplify the voltage to almost 50V.
This allowed a larger current to flow through the inductor, thereby increasing the strength of the
magnetic field, and allowing the Lapview watch to detect a signal from up to 5 feet away.
The ATMEGA168V 10AU is a 32 pin surface mount microcontroller that is extremely small (approximately 8 square
mm). It is able to operate at 1.8V, making it a perfect lowpower device for the Lapview Watch.
Professor Philip Farnum
SPECIAL THANKS TO
Anita Choi
Sid Deliwala
Kyle Doerksen
Neal Mueller
DEMO DATE
Thursday April 24th, 2008
The μOLED-96-G1 is an embedded intelligent organic LED
display module. It is 0.96” (diagonal) with 96x64 pixel
resolution. It operates at 3.3V, once again making it an ideal
display for the Lapview watch. The easy 5 pin interface (Vcc,
Ground, Rx, Tx, Reset) made it easy to interface with the
ATMEGA168V Micro-controller.
GROUP 9
The Microchip TC4422A is a high-speed , single output
MOSFET driver. The TC4422A was crucial in amplifying the
voltage from the 9V battery to 50V, which was then used to
drive the inductors.
GROUP 9