Real-time swimmers´ feedback based on smart infrared (SSIR) optical wireless sensor

An IrDA link based on a serial infrared transceiver has been designed and implemented for real-time swimmers´ feedback. A wrist-mounted accelerometer provided stroke information to the transmitter. The signal was detected using a photodiode detector. Both the transmitter and receiver units measured 27 ´ 19 mm. Propagation experiments in air and under water were performed in a glass tank (91 ´ 39 ´ 45 cm) to validate the system. The maximum link length in air was 2 m and in still water 70 cm. In water with bubbles, the range reduced to 50 cm. This distance is sufficient for wrist´head communications during swimming. The information transmitted was the time duration of one complete stroke, which was updated every stroke and presented to the swimmer using an RGB LED mounted on the goggles. The hardware, software and implementation methods for the IrDA system are described.