I have a cheap heart rate monitor.  Using my oscilliscope and a coil of
wire right up against it I find that each heartbeat is transmitted as an
8mS long 5kHz pulse.

I'm building a logging bicycle computer, which I'd like to have read the
pulse from this heart rate monitor.

I believe that the basic heart rate sensor sensor is going to consist of
a coil and a cap that resonate as 5kHz.  I can design that myself (and
will have to since I'll be making the coil 1-2" in diameter and need to
use a tiny cap).

What I need is a simple circuit, ideally as few, small, and low power as
possible components that will enable the PIC to determine if the coil is
resonating, and thus a heartbeat just occurred.

I imagine that it could be accomplished with a transister (or two) and a
few passives, but I really don't know.  Perhaps rectify the signal, then
filter and amplify it...?  I would like the range to be reasonable (1
meter), so I don't think a completely passive solution is going to do
well enough.

The circuit will have 2-3vdc available, and need only put out enough
signal so a PIC running at the same voltage can detect the pulse.

Noisy or dirty solutions are ok if they reduce component count and power
consumption and are still readily filtered and detected properly with
some simple PIC code.  Lastly, if I got all my wishes, I could simply
change the coil and cap and detect a wider range of signals so it oculd
easily be adapted to other heart rate monitors.  Mine is a Sigma PC 6.
Anyone have a polar they could test the output of?

I did a brief search and found a few resources.  Most of the homebuilt
HRMs consist of the infrared LED through the finger/earlobe/etc (blood
absorbs infrared).
One sensor kit here reads a polar HRM:
http://www.matrixmultimedia.co.uk/picmicro/picprods_1.htm
But it uses a seperate polar sensor to read it, which appears to be
interfaced to lego mindstorms here:
http://www.smm.org/heart/tools/heartsensor/top.html

-Adam

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu