Inexpensive transistorized circuit provides reliable analog indications of heart rate in response to preamplified electrocardiograph signal applied to its input

Vick, H. A.

English

NASA Technical Reports Server

FERom +18 to 32 Volts +1 Volt 0.
Output Waveform 
- To Recorder 
EKG Input
January 1965
	
Brief 65-10010 
NASA TECH 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Inexpensive, Stable Circuit Measures Heart Rate 
High Gain Amplifier One-Shot Multivibrator 	 Switch Integrator	 Series Regulator 
r-------- ----------------ir-------------  -
The problem: Although circuits for measuring 
heart rate have been available for some time, they 
have either been more complex than basically neces-
sary in order to accommodate a wide range of applica-
tions, or have been available only as part of an electro-
cardiograph (EKG) system. There is a need for a 
simple, inexpensive circuit that will provide a reliable 
indication of average heart rate. 
The solution: An inexpensive, stable, transistorized 
circuit that provides an accurate analog indication of 
average heart rate in response to a preamplified EKG 
signal applied to its input. The device provides a meter 
indication of heart rate in addition to a proportional 
output voltage which may be fed to a high-input im-
pedance recorder. 
How it's done: The circuit uses the R--wave (posi-
tive spike) of an EKG signal to trigger a pulse gener-
ator. The metering circuit is basically an integrator 
which uses the constant-width, constant-amplitude 
pulses from the generator to produce a voltage
proportional to the frequency of the pulses. The 
EKG input signal is applied across the trigger 
level control R 1 which is set so that D 1 passes 
only the large positive spikes (R-waves) of the signal. 
This spike is amplified by a high-gain, common emit-
ter amplifier (Q 1 and associated circuittv) and then 
coupled to a one-shot multivibrator through C 1 . The 
multivibrator 02 and Q 3 ) produces a constant-dura-
tion, constant-amplitude, square-wave output for 
every input pulse from the amplifier. With no pulse 
present, Q 3 is conducting and Q 2 is cut off. Arrival 
of the negative pulse at the base of Q 3 decreases its 
collector current, producing a positive pulse at the 
base of Q 2 . This causes an increase in the collector 
current of Q 2 and a corresponding negative shift of its 
collector voltage. This negative pulse is fed back to the 
base of Q 3 causing a rapid switch in the conditions of 
Q 2 and Q 3 (Q 2 turns on, Q 3 turns off). The pulse 
duration is determined by the C 3 R3 time constant 
after which Q 2 and Q 3 revert to their original states. 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern- 
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document. 
https://ntrs.nasa.gov/search.jsp?R=19650000010 2020-03-11T17:16:38+00:00Z
The square-wave pulses from the multivibrator are 
coupled to the base of Q 4 which controls the average 
rate of current flow to the resistor-capacitor integrat-
ing network. An increase in the frequency of the 
square-wave signal causes an increase in 0 4 's collector 
current and a corresponding increase in the voltage 
across C 2 . Output for a recorder with a high-input 
impedance (10,000-ohms minimum at 1 volt) is avail-
able directly across C 2 . Resistor R 2 is adjusted to pro-
vide full-scale deflection of M with an average heart 
rate of 200 beats per minute. An internal series voltage 
regulator is provided in the circuit for portable opera-
tion with batteries. If a constant voltage source is 
available, the regulator circuit (Q 5 and associated cir-
cuitry) may be omitted.
Note: Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537. 
Houston, Texas, 77001 
Reference: B65-10010 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C., 20546. 
Source: Howard A. Vick 
(MSC-95) 
Brief 65-10010	 Category No. 01


Inexpensive, stable circuit measures heart rate

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