Dan Michaels email (remove spam text)
At 09:43 AM 12/22/00 -0600, you wrote:
>Seasons' Greetings to all...
>I was wondering how do the Polar heart monitors
>work? Do they use a microphone or something else.
>I didn't think you could use a vibration sensor, (I don't
>know what this would even be, exactly), because they
>work while the person is running and exercising, etc..
Electrical pickup via electrodes on under side of belt,
triggers a transistor amp which is biased for class C
operation [normally zero battery drain], which pulses
some kind of LC ckt that rings at about 2-5Khz for a
couple of msec. Wrist watch uses a simple inductive
tuned ckt to pick up the signal from the belt.
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