Frequency Counter

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singhak

Joined Oct 18, 2004
13
I am currently doing a project that involves making an infrared based heart rate meter. If anybody has done same thing then I would appreciate any info.

Specifically , I wanted to know abt suppose I have digital pulses(heart beats), then how do I count the heart rate. I know how to make a conventional frequency counter in which counting time is 1 sec, but here the counting time is 1 min, so if I do by that method then the problem is of generation of a pulse of less than 1 Hz freq.
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

Freq counters have an internal time base, usually a crystal oscillator. The output is counted to give the interval that the counter for the external signal increments. My cheapo counter has 1 sec and 10 sec counting intervals, for instance.

For your purposes, you need a time base that will allow you to count the heart beats for 60 seconds. The total count will be beats per minute. Any low frequency oscillator will do nicely - a 1024 Hz tuning fork for watch functions should be easy to come by. Just count 61,440 oscillations and there is your one minute period.
 

thingmaker3

Joined May 16, 2005
5,084
A couple of my in-laws work in health care. They tell me that only 15 seconds are used to determine heartrate. (Multiply counted beats by four for BPM.) I'm told the rest of the minute is actually used to observe respiration.

For 15 seconds, 15,360 oscillations would do the trick. The count would have to increment by four for each hearbeat if this option is used.
 

009hnoor

Joined May 7, 2015
1
The total count will be beats per minute. Any low frequency oscillator will do nicely - a 1024 Hz tuning fork for watch functions should be easy to come by.


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