🚀 go-pugleaf

I asked for ideas for transducers for a heart-rate monitor.
This is a summary of replies.  Many thanks to 

louis@asterix.drev.dnd.ca (Louis Demers)
"The Boov..." <TDB@icf.hrb.com>
regmad@gsusgi2.gsu.edu (Michael de Kraker)
wtm@uhura.neoucom.edu (Bill Mayhew)
rpw3@rigden.wpd.sgi.com (Rob Warnock)
ucapb6t@ucl.ac.uk (Mr T Phillips)
"George L" <george@alpha.ee.ufl.edu>
root@fangorn.hacktic.nl

The heart reate monitors whose transducers clip on the earlobe or
finger are based on infrared radiation emission and detection.
IR from an IR emitting diode passes through the earlobe with
varying amounts of ease, depending on the state of blood flow.
Of course, the pattern of blood flow through the earlobe corresponds
to the heart beat, and this pattern can be detected by a photo-
transistor.

One respondent suggested that coil type transducers do exist (current
in the coil reacts to changes in magnetic flux), but they are susceptible
to noise, and will not work well on obese persons.

ECGs, and most heart rate monitors it seems, use electrodes (not really
transducers, because they don't convert from one thing to another).
Electrodes are used simply to measure potential differences between
different parts of the body.  Electrodes can be pushed up against
the skin, inserted under the skin, or inserted through a vein to
some internal part of the body.

All of the literature I managed to find pertained to ECGs and their
design, rather than heart rate monitors.  It should be easy enough,
however, to build a much simplified version of an ECG.  I have
decided to look into the possibility of purchasing a heart rate
monitor, let it do the detection and amplification, and use a PC to
monitor the output of that stage.  Hopefully that would be a
TTL-level pulse.  I suppose I could commandeer the seven-segment
display signals, but those would not be TTL level voltages, would they?
Any ideas on how to approach this?

Anyway, here is a blurb about ECGs.

The ECG records a picture of time varying potential differences
across various parts of the body.  The potential differences
are cyclic, of course, and if you measure the time between landmarks
in adjacent cycles, you can calculate the instantaneous heart rate.
Of course you could use an ECG as a heart rate monitor, but it
would be like <insert your favorite overkill simile here>.

In standard ECG recording there are five (not 12) electrodes
connected to the body: right arm, left arm, left leg, right leg, and
chest.  There are six standard positions for the chest electrode, and
the other four electrodes are combined in different ways.  The net
result is that twelve different potential differences are considered.  
Each of these is called a lead, which is where the term 12-lead ECG
comes from.  Each lead gives a picture of the heart's electric signals
from a different angle so that the different parts of the heart
can be isolated.  If you want a more detailed/accurate description
of ECG recording than that, you should look up one of the references
provided below.

In _Radio Electronics_, July 1991, pages 31-40, 46, 88, there is
an article by H. Edward Roberts, M.D. describing how to make a
PC-based 12-lead ECG.  (This article seems to be part one of two,
but I didn't look for the second part).  The article includes
a parts list, and the address of a company which can supply
various subsets of the parts (or a complete kit $289).
The address is
    DataBlocks, Inc.
    Glenwood, GA 30428
    (912)568-7101

In _Radio Electronics_, November 1991, pages 49-57, there is
an article by Joe Jaffe on building a doppler-ultrasound heart
monitor, which can be used to listen to a person's heart
(rather than monitor it's rate).
The following company can supply various kits including subsets
of the required parts, as well as a full kit  $135 or a completely
assembled instrument $189:
    Products & Processes
    9450 Mira Mesa Blvd
    Suite #B-321
    San Diego, CA 92126
    (619)566-0711

Here are some references for those interested in biomedical technology:

   AUTHOR: Carr, Joseph J.
    TITLE: Microcomputer interfacing handbook : A/D & D/A

PUBLISHER: Tab Books, c1980.
 SUBJECTS: Microcomputers.   Digital-to-analog converters.   
           Analog-to-digital converters.
           MATERIAL: Book

-------
   AUTHOR: Carr, Joseph J.
    TITLE: Data acquisition and control : microcomputer applications for 
           scientists and engineers
PUBLISHER: Tab Professional and Reference Books, c1988.
 SUBJECTS: Physical measurements--Data processing.   Mensuration--Data 
           processing.   Microcomputers.
-------
   AUTHOR: Carr, Joseph J.
    TITLE: Designer's handbook of Charge/LcRq
PUBLISHER: Academic Press, c1991.
 SUBJECTS: Electronic instruments--Design and construction.   Integrated 
           circuits.
-----
   AUTHOR: Carr, Joseph J.
    TITLE: Introduction to biomedical equipment technology

PUBLISHER: Wiley, c1981.
 SUBJECTS: Medical instruments and apparatus.   Equipment and supplies.   
           Electronics, Medical.   Biomedical engineering.

-----
   Willis J. Tompkins and John G. Webster, EDs, _Design
   of Microcomputer-Based Medical Instrumentation_, Prentice Hall, 1981.
--
Todd Kelley                       tgk@cs.toronto.edu
Department of Computer Science
University of Toronto