Lapview – The Swimmer’s Watch GROUP 9 PRESENTERS DEMO DATE SPECIAL THANKS TO ADVISOR PRESENTERS Thursday April 24 th, 2008 Department of Electrical and.
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Lapview – The Swimmer’s Watch GROUP 9 PRESENTERS DEMO DATE SPECIAL THANKS TO ADVISOR PRESENTERS Thursday April 24 th, 2008 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. 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 Suman Addya EE ‘08 Vasudev Kulkarni CTE ‘08 GROUP 11 Professor Philip Farnum Anita Choi Sid Deliwala Kyle Doerksen Neal Mueller System OverviewSoftware Overview Hardware Components 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. 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. 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. 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 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. 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. The ATMEGA168V 10AU is a 32 pin surface mount micro- controller that is extremely small (approximately 8 square mm). It is able to operate at 1.8V, making it a perfect low- power device for the Lapview Watch. 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. 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. 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.