• on Test & Measurement
  • Published in issue 7/2012 on page 68
About the article

Lengths Counter for Swimmers

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

Lengths Counter for Swimmers

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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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

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

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