Machine Design

Computer on a shoestring

A device that clips to a shoelace lets runners and walkers monitor performance while on the go.

The FS-1 speedometer from FitSense, Wellesley, Mass., weighs only 20 gm and measures speed, distance, and calories burned. Real-time data is sent to a wrist display over an RF link.

The heart of the FS-1 is a PIC microcontroller from Microchip Technology Inc., Chandler, Ariz. The 8-bit PIC16F877 is a 20-MHz processor with 8 kbytes of program Flash memory and 2 kbytes of RAM for data storage. In-circuit serial programming makes it easy to reprogram for quick field upgrades.

Traditional hip-mounted pedometers count steps and multiply by a fixed stride length. However, stride length can vary with speed and conditions, leading to inaccurate readings. The FS-1 uses an accelerometer in the foot pod to measure forces on the top of the foot. The data is then used to generate a stride profile of each step and to calculate speed, distance, and calories burned. A two-way transceiver also lets the wrist display communicate with the foot pod and send calibration constants such as weight.

An optional two-lead EKG chest strap measures and displays heart rate in real time on an optional monitor. Stored data can also be uploaded to a PC via an RF link for analysis after a workout.

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