The Request
Hi,
Hope you are fine. 🙂
The purpose of writing here is to share with you an idea of a project - to design a "heart rate monitor alarm" which can be made by using commonly available low cost components and which will produce an audible alarm whenever the pulse rate of anyone is found to be abnormal. It should meet the following conditions as well:
a. Compact and light weight, therefore portable
b. Consume minimum power, therefore should run 24x7 for a month or two from a couple of AA batteries or a 9 volt pack
c. Should be fairly accurate in it's performance
I know there are many such circuits available on the net but their performance and reliability are questionable. The unit can be very useful especially for elderly people (with / without a heart disease), for patients who are bed ridden and so on. When the heart either beats at a rate higher/lower than a set average threshold value, the alarm will sound loudly enough to alert people around the patient.
I hope that my proposal is clear to you. However, if you have any doubt, please drop me an e-mail.
Thank you,
Kind regards,
Raj Kumar Mukherji
The Design
In the previous post we learned how to make a heart rate sensor circuit with processor, which can be appropriately used in the proposed critical heart rate alarm circuit.
The
application presented here is for reference design purposes only and is
not intended for any life-saving or medical-monitoring use.
Referring to the diagrams above, we are able to see a couple of circuit stages, the first being the heart rate sensor/processor with an integrated frequency multiplier, while the second in the form of an integrator, comparator.
The upper signal processor design has been comprehensively explained in the previous post, the additional voltage multiplier which is been integrated to the processor uses the IC 4060 for multiplying the relatively slower heart rates into a proportionately varying high frequency rate.
The above proportionately varying high frequency heart pulse rate from pin7 of IC 4060 is fed to the input of an integrator whose job is to convert the digitally varying frequency into a proportionately varying exponential analogue signal.
Finally this analogue voltage is applied to the non inverting input of a Ic 741 comparator. The comparator is set through the attached 10k preset such that the voltage level at pin3 stays just below the reference voltage at pin2 when the heart rate is in the vicinity of the safe region.
However if the heart rate tends to increase over the critical region, a proportionately higher voltage level is developed at pin3 which crosses the pin2 reference level causing the output of the opamp to go high and sound the alarm.
The above set up only monitors and alarms regarding the higher critical heart rate, in order to achieve a two way monitoring, meaning to get an alarm for both higher and lower critical heart rates...the second circuit comprising the IC555 and IC741 could be entirely eliminated and replaced with a standard IC LM567 circuit set to keep its output low at the safe pulse rate, and go high at the up or down critical rates.
signal conditioning circuit consists of two identical active low pass
filters with a cut-off frequency of about 2.5 Hz. This means the maximum
measurable heart rate is about 150 bpm. The operational amplifier IC
used in this circuit is MCP602, a dual OpAmp chip from Microchip. It
operates at a single power supply and provides rail-to-rail output
swing. The filtering is necessary to block any higher frequency noises
present in the signal. The gain of each filter stage is set to 101,
giving the total amplification of about 10000. A 1 uF capacitor at the
input of each stage is required to block the dc component in the signal.
The equations for calculating gain and cut-off frequency of the active
low pass filter are shown in the circuit diagram. The two stage
amplifier/filter provides sufficient gain to boost the weak signal
coming from the photo sensor unit and convert it into a pulse. An LED
connected at the output blinks every time a heart beat is detected. The
output from the signal conditioner goes to the T0CKI input of
PIC16F628A. - See more at:
https://embedded-lab.com/blog/?p=1671#sthash.kPQKViQ
signal conditioning circuit consists of two identical active low pass
filters with a cut-off frequency of about 2.5 Hz. This means the maximum
measurable heart rate is about 150 bpm. The operational amplifier IC
used in this circuit is MCP602, a dual OpAmp chip from Microchip. It
operates at a single power supply and provides rail-to-rail output
swing. The filtering is necessary to block any higher frequency noises
present in the signal. The gain of each filter stage is set to 101,
giving the total amplification of about 10000. A 1 uF capacitor at the
input of each stage is required to block the dc component in the signal.
The equations for calculating gain and cut-off frequency of the active
low pass filter are shown in the circuit diagram. The two stage
amplifier/filter provides sufficient gain to boost the weak signal
coming from the photo sensor unit and convert it into a pulse. An LED
connected at the output blinks every time a heart beat is detected. The
output from the signal conditioner goes to the T0CKI input of
PIC16F628A. - See more at:
https://embedded-lab.com/blog/?p=1671#sthash.kPQKViQC.dpuf
Sir
Photo Transistor will work in place of
IR Photo diode.
yes, it should work.
Dear Swagatam,
Thanks for tendering my request.
I think it is going to be a very useful project if constructed carefully. However, in the last paragraph of this article, you have left your readers to design a LM567 based circuit themselves 🙂
I have searched all your blogs related with the LM567 projects. However, could not find any where the LM567 will keep its output low at the safe pulse rate (frequency), and go high at the up or down critical rates. I may be wrong in my search. Therefore, would appreciate further inputs from your end on this.
Thanks and regards,
Raj Kumar Mukherji
Thank you Raj,
I think a LM567 IC would not be appropriate since it's too precise and will sound the alarm even if the rate deviates by 3 to 4% which could be too early.
Instead we could use a LM3915 IC here designed to detect voltage level through 10 steps. It could be connected in place of the IC 741 stage, and its preset set such that during normal heart rates the middle 5th and 6th outputs stay active…during higher this would go on shifting towards 7,8,9,10 outputs while during lower rates this would shift towards the 4,3,2,1 outputs….except the 5.6 outputs rest all could be tied up together through individual diodes with each of the outputs and used for powering the alarm.
An example circuit could be seen here:
https://www.homemade-circuits.com/2013/08/make-this-10-step-battery-voltage.html
the 10k connected at pin9 will need to be removed and connected to R9 diode cathode in the 555 circuit from the above article.