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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.Introduction: Underwater optical wireless IrDA link performance was evaluated and reported in [1] based on the measurement of the time jitter by looking for the impact of air bubbles and transmission through the water surface. In [2] three axis accelerometer data was transmitted at 2400 bps over a 1 m underwater path at 10 cm depth using frequency shift keying (FSK) at very low frequency (VLF). The modulation frequencies used were 10 and 12 kHz. The modem was designed, tested and implemented for low-cost, short-range, digital communications. In [3] a ring of eight LEDs was implemented to determine the preferred transmission position for the smart sensor. The modem was based on using FSK and on-off keying (OOK) at the transmitter with eight green LEDs to provide omnidirectional coverage from the wrist. Green light was used for minimum attenuation in water (includes both absorption and scattering) [1]. The receiver used was based on an integrated detector preamplifier (IDP).Experiments conducted in a swimming pool showed that the link was intact for 54.3% of the time during freestyle swimming, while 60.3, 45.25 and 50.5% was the link viability in breaststroke, backstroke and butterfly, respectively, when all the LEDs on the wrist were transmitting. When each LED was switched on individually, the results showed that only three LEDs were required to maintain these statistics. The requirements for the device were wearability to prevent disturbance to normal swimming action and more than 1m transmission distance (wrist to head). The data recorded should be processed at the transmitter and useful information sent to the receiver, e.g. stroke rate, lap rate and swimming style. This Letter presents a smart serial or standard infrared (SSIR) system tested for short-range swimming applications based on stroke rate feedback to maintain the stroke rate at a predetermined swim plan.

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