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The velocity of a swimmer can be determined from the stroke rate and the stroke length or by integrating the forward acceleration. In competitive swimming, these parameters are very important for race planning. This paper presents a wrist mounted accelerometer and optical wireless communications to display goggles to give real time feedback to a swimmer during swimming. The system data rate is 2.4 kbps ON-OFF keying modulation for the optical wireless signal. The system uses visible light communication in the green-blue wavelength. Design challenges include interference from bubbles and strong background light. The final device is low cost with low power consumption and small size. Intra-stroke transmit times are scheduled using the acceleration sensor data. Experiments are conducted in air and under water for this system to optimize the link availability. Algorithms for finding the absolute maximum of the y-axis acceleration for each stroke cycle and the goggles display decision are implemented at the transmitter and the receiver, respectively. Hardware, software, and implementation modifications to improve the system are successfully tested.
Date of Publication: Aug. 2013