Soon Lee wrote:
>Hi everyone
>
>is there any circuit that i can use to measure, detect, heart pulse?
>
>thanks
>

Hi Soon Lee,

I have some experience with most of the methods people have been
describing in this thread. If you just want to know the heartrate in
a resting situation, the IR or acoustic methods will probably be ok.
My exercycle has an earlobe device, but it is so uncomfortable I
have never used it. The finger tip devices don't work so well for
exercising - although some devices like this have been sold in the
past, they do not seem to be very popular. Acoustic methods will
probably require a lot of filtering to eliminate movement and
breathing artifacts.

Direct electrical measurements [EKG/ECG] are actually quite easy, as
the heart signals are in the mV range. A simple AC-coupled instrumentation
amp will do it. Electrodes are not even all that critical. 2 small metal
plates, located horizontally 7-8 inches [15-17 mm] apart halfway down the
chest work well. This is essentially what the Polar heartrate devices
use - a fairly snug elastic band around the chest, with 2 metal plates
that you moisten with saliva. People run marathons using these things.
No special electrodes or surface preparation are required for simple
measurements.

Muscle signals [EMG] are typically in the 500-1000 hz range, and can
usually be filtered out of the EKG signal, using a 100 hz or so
low-pass filter.

Additionally, you can look at output of the instrumentation amp on a
scope, and actually see all of the EKG waves. You can move the electrodes
around, and do your own medical diagnosis - [just kidding - in america
you go to jail for impersonating a doctor - but the waves are fun to
look at].

NOTE - if you do connect an amp to your chest, you want to be careful
you do not electrocute yourself - this is **THE** big issue here.
Commercial devices use isolated power supplies and/or optoisolated
outputs.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================