[time-nuts] time-nuts Off topic project sort of heart rate monitor

Greg Broburg semiflex at comcast.net
Wed Feb 20 13:01:59 EST 2013

Hello Paul;

I was an IPG designer many moons ago. For the
input amplifier we had a bandpass centered at
22 Hz with production testing at low end of 5 Hz
and high end of 35 Hz. The input circuits would
make a threshold comparison and if the input
was above the set value (typically 2 mV) arriving
from the lead inside the heart, it would trip other
circuits. There was a refractory sense window
where if the unit pulsed into the heart it would
ignore for that period or if the heart was detected
on its own it would invoke the same refractory
period. Typically this was 250 - 300 mS.

Note that physical issues can raise the heart
rate much higher than 90 BPM. It is not unusual
for heart rate to go to 140 BPM with high blood
sugar levels.

I agree with the idea of using photo plethsymography
have worked on this method for other designs. You
will have a huge range of light levels to deal with and
can use a microcontroller with AD and DA ideas to
help find the signals. I would consider both methods
perhaps combine for best performance.

If using photo ideas look for off of the shelf sensors
to get started. Pulse oximetry sensors will have 2
LEDs for oxy measurement, only one is needed for rate.

>   [time-nuts] Off topic project sort of heart rate monitor NEED BEATS
> *Paul Cianciolo*paulc at 
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> Hello Folks,
> I am working on a project intended to convert an analog ECG signal to a voltage proportional the heart rate,
> The actual electrodes instrumentation amp is pretty much working fine  so no worries there.
> The problem is, and here is where the relationship to time nut comes in.
> The signal output from the instrumentation amplifiers will be at a rate of approx 60 BPM or pulses, up to perhaps 90 BPM.
> The purpose of this apparatus is to print a rolling chart on the screen of a computer of heart BPM and then try different technicues of meditaion  and calming technicues to lower my heart rate for short periods of time.
> My first tthought was a frequency to voltage IC like the LM2907 or the 2917 but I get the impresiion from the data sheets that these chips will not work at these very low  1 Hz applications,
> Then I thought maybe one of the frequecy counters could be configured as a rate meter and output a proportional voltage I need.
> No luck here either.
> Te latter components seem tobe somewhat time relatedand that is why I posted here.\\
> Thank you for reading this and for any suggestions you folks might offer.
> PaulC

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