[time-nuts] Off topic project sort of heart rate monitor NEED BEATS PRE MINUTE TO ANALOG VOLTAGE

Stanley timenuts at n4iqt.com
Thu Feb 21 12:26:00 EST 2013

One of my first programming projects was a RCA 1802 micro replacement for a 
ware-able Holter monitor. The idea was to record a series of 8 second strips 
and assign a value of how important they were. This value was used to decide 
which ones to save for later viewing. The area under the curve and slope 
were important measurements, both easy to calculate as the area was just a 
sum of values and slope was a difference between two values. The hard part 
was separating PVC, PAC from artifacts . Id of the QRS complex was not a 

The Cross assembly was done on a PDP-15 :-)


----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: <time-nuts at febo.com>
Sent: Wednesday, February 20, 2013 4:49 PM
Subject: Re: [time-nuts] Off topic project sort of heart rate monitor NEED 

> On 20/02/13 02:23, Bob Camp wrote:
>> Hi
>> The first layer to the onion is that the ECG signal is a bit complex. 
>> There's also likely to be a bit of this and that on it.
>> How about taking the output of the instrument amp into the A/D port on a 
>> cheap PIC? That would let you do some AGC and dynamic filtering. At even 
>> a modest sample rate (say 10 KHz) the heart rate could be worked out in 
>> software. I think I'd run a PWM out and drive an analog meter with it.
> Exactly which platform you choose isn't as important, but I was thinking 
> essentially the same.
> Frequency measurement using time between suitable trigger-point on the 
> waveform would allow simple conversion into BPM scaled frequency. A 
> suitable exponential lag filter can then average the values, and allow for 
> a few suitable smoothing filter bandwidths.
> AGC and trigger detector, possibly some pre-filtering, should be the main 
> things to look at, the remaining is relatively trivial.
> There are Agilent function generators (33120A or 33250A if I recall 
> correctly) with heart-wave shapes which would be good to use for testing.
>> The nice thing about keeping it simple is being able to run it off a 9 
>> volt battery. That takes care of a *lot* of issues.
> Oh yes. Unless the monitoring system being tapped isn't handling most of 
> the isolation/loop issues.
> Cheers,
> Magnus
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