• about Test & Measurement
  • Published in issue 7/2012 on page 68
About the article
Lengths Counter for Swimmers

Lengths Counter for Swimmers

An example application using speech synthesis, an accelerometer, and a magnetometer

There’s no lack of distance counters for walkers or cycling; but swimmers are reduced to mentally totting up how many lengths of the pool have been complete, for want of a counter suitable for their favourite sport. The project described on these pages got designed to build an electronic solution that takes care of this tedious counting. The result is a device that’s reliable, handy, light, discreet – and inexpensive.

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Extra info, Update
Main technical specifications
• small unit worn on the back of the swimmer’s head, under the goggles strap
• vocal announcement of distance without waterproof earpieces
• error rate < 5 %
• powered by two AAA cells
• compact: 96 × 47 × 24 mm
• system open to lots of other applications

Main components used in project
PIC18F27J13-I, Microchip, MCU, 8 bit, 128 KB Flash, 3 KB RAM (QFN28)
MAG3110FCR1, Freescale, 3-axis magnetometer w. I2C interface I2C (DFN10)
MMA7361LCR1, Freescale, 3-axis accelerometer w. analogue outputs (LGA14)
SSM2301RMZ-R2, Analog Devices, 1,5 W classe D audio amplifier (MSOP8)
ASLS-2, Assemtech, Acceleration sensitive switch (2G),
OKW Smart Case M A9066109 + A9166001 : recommended housing
ADS02008MR-R Projects unlimited : mini LSP 8 Ohm, Ø20 mm