How to convert accelerometer data from excel into frequency

Hello I am trying to convert the accelerometer data I collected from the MPU 6050 in the Z axis to vibrational frequency. I am powering a small vibration motor at 82 duty cycle expected 130 hz according to the data sheet. I got some advice from my teacher to get a live recording instead of my previous post. So I got the live value in ardunio and wrote it to excel. Using this previous post "How to use FFT in matlab using importated data in time domain excel file." I got my data. However I am not even close to my expected frequency. Can someone help me figure out what is wrong?

I used this excel file the first column is time in miliseconds and the last column is what im interested in which is accel readings in the Z axis in gravitational force.

My current output is in Z Readings below but im expecting something closer to the image below with the frequency at 130 hz.

Answer 1

[Star Strider]

The sampling frequency is too low to detect a 130 Hz vibration:

A = readmatrix('DutyCylce82Vals2.csv');
A(:,1) = A(:,1)*1E-3;                                       % Convert To Seconds
Ts1 = mean(diff(A(:,1)));
Fs1 = 1/Ts1;

This calculates the mean sampling frequency (note that the signal is also not regulalrly sampled, and it needs to be) to be about 41 Hz. In order to detect a 130 Hz vibration, the sampling frequency must be at least 260 Hz (sampling interval at most 3.84 ms), and ideally much higher than that, for example 300 Hz, with a sampling frequency of 3.33 ms.

[Alexander Tan]

Thank you for the quick reply Star Strider. So in order to get an increased sampling frequency? Looking at your work and the variables in MATLAB I would need to lower the time between each sample to increase the sample frequency? I will try messing around with changing the rate in Ardunio thanks for the help!

[Star Strider]

My pleasure.

‘Looking at your work and the variables in MATLAB I would need to lower the time between each sample to increase the sample frequency?’

Yes.

(1) The sampling intervals have to be constant, and

(2) The sampling frequency has to be more two times the highest frequency you want to recover from your data.

[Yash Kadu]

Hey can you help me in converting the accelerometer data into frequency data?