Low-cost, modified cassette is part of system that accepts biomedical data for storage. System accepts wide range of data and is compactly packaged for portability. Standard office recorder with automatic level control, multiple inputs, radio, and battery operation may be used for recording stage

Wilbur, R. L.

English

NASA Technical Reports Server

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June 1973	 B73-10167 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Biopotential Monitoring With Inexpensive

Office-Type Cassette Recorders
Biopotential Monitor, Block Diagram 
The problem: 
Automatic monitoring of vital signs of hospital and 
ambulatory patients is becoming more common as new, 
sophisticated medical treatments become available. How-
ever, medical personnel handling large numbers of cardiac 
outpatients through clinics or home or office routines 
need new methods to acquire, store, and analyze the 
medical data. One method is to place the data on mag -
netic tape. Medical-grade recording systems exist to 
hard-wire-record biopotential signals, but they are so 
expensive that they price themselves outside most 
physicians' means. An inexpensive alternative, office 
tape cassettes, are not currently used because their low 
frequency limit is higher than the frequency of bio-
medical signals such as ECG's
The solution: 
A low-cost, modified cassette is part of a system 
that accepts biomedical data for storage. The system 
accepts a wide range of data and is compactly packaged 
for portability. 
How it's done: 
The system, as shown in the illustration, includes 
three subsystems: 
I. A signal conditioner - modulator/transmitter. 
2. A cassette recorder - FM receiver. 
3. A demodulator. 
The signal conditioner amplifies the biomedical signal 
from the electrodes. It is pulse-rate modulated at a 
center frequency best suited for the particular recorder 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19730000167 2020-03-17T07:11:31+00:00Z
used. To amplify the low-level biopotential signals, a 
micropower programmable amplifier is used. It has 
a large open-loop gain, high input impedance, high 
common-mode rejection, low offset current and voltage, 
and a very low power consumption. 
The amplifier/modulator raises the low-frequency 
signals by 2 to 5 kHz. This rejects AM noise and allows 
FM broadcast of the signal with a minimum of circuitry. 
A standard office recorder with automatic level 
control, multiple inputs, AM-FM radio, and battery 
operation is used for the recording stage. These are 
available at a very reasonable price and offer a sub-
stantial savings over conventional medical systems. 
The demodulator accepts any pulse-rate modulated 
signal on the tape. It consists of a zero-crossing detector/ 
one-shot multivibrator and an integrator. An output 
signal from the tape recorder is sampled by the zero-
crossing detector and provides a sharp transition for 
each zero crossing. Negative triggers into the multi-
vibrator produce positive output pulses which are 
smoothed by the integrator to reproduce the original 
signal. 
Becaise this type of demodulator is not locked to 
the modulator, it is independent of the modulating 
frequency and battery voltage fluctuations. Therefore,
accurate time measurements are not assured. If accurate 
time measurements are needed, a phase-locked loop 
demodulator must be used. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10167 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: R. L. Wilbur of

Southwest Research Institute
under contract to

Marshall Space Flight Center

(MFS-22566)
[I: 
B73-10167	 Category 02, 05


Bipotential monitoring with inexpensive office-type cassette recorders

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