Finding frequency of your input signal

[anupam2016]

Hello,

I am trying to aquire a PPG(photoplethmysography) signal through LIFA.It basically measures the relative blood volume changes using a IR photodiode and a IR led ..This is the circuit which I have made for aquiring.The V_0 is taken through the A0 input of the arduino.The VI which I am using is attached.

Now the question is,

1. Can I know what are the frequencies in my signal.I tried using spectral measurement (using the power spectrum option) , but it gave a data type error.

2. As I am trying to get information about heartbeat, that means 1 beat in 1.2s, meaning 1.2Hz is the frequency.I tried creating a butterworth filter of pass frequency 1.2 plus or minus 0.5 but it gave a nequist theroem error.How do I use that.

Thank You very much

Anupam

[ijustlovemath]

You need samples at twice the rate of your highest frequency to pull out the necessary information without aliasing. There are many ways to do what you want to do, but we need to see you .vi's to actually help. Save for LabVIEW 2013 for me specifically if you can.

[RavensFan]

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@anupam2016 wrote:

2. As I am trying to get information about heartbeat, that means 1 beat in 1.2s, meaning 1.2Hz is the frequency.I tried creating a butterworth filter of pass frequency 1.2 plus or minus 0.5 but it gave a nequist theroem error.How do I use that.

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Double check you rmath, you've got it backwards.  1 beat in 1.2 seconds is 0.8333 Hz.  Hertz is "per second".  1 beat per 1.2 seconds is 1 divided by 1.2.

[Bob_Schor]

Do you understand the math behind sampling an analog signal and estimating its frequency content?  Some specific numbers that you need to consider (and describe to us) are:  Sampling Frequency, number of samples acquired in a record, the maximum and minimum frequency you expect to see, and the frequency "accuracy" (or "difference") you expect.  The last means are you interested in distinguishing between 50 and 51 Hz, or is it enough to distinguish between 50 and 40 Hz.

Bob Schor

[anupam2016]

I have uploaded the file,in the question.(ppg.vi)