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Measuring bioimpedance using FFT

i Hi to everyone, 


I am student, and i have to do project "Measuring bioimpedance using FFT" for my college to pass the exam. I got several points (instructions) how to do it but they are poorly explained and I am not enough good programer. Up to now i made some points but I don't know if they are good :)..... I will write these instructions, and i please some good programers to help me :)...


1. First task is to configure A/D and D/A conversion of two analog (voltage) channels, with some parameters like: frrequency of generated output samples (100 kHz), frequency of signal( 1kHz), frequency of sampling of input signals...


2. Second task is connecting analog output directly on the analog inputs and compare input and output signals. 


3. Calculate the FFT and show the results.


4. Analysis of the phase shift of the two input signals.


5. Compensation of the phase shift


6. I stopped on this point because I don't have the idea how to realize that. I have to calculate the impedance based on informations of amplitude and phase, and the information of referent resistor. I have to calculate the impedance (the real and the imaginary part), reaktance and the C or L. Also i have to calculate the amplitde and phase of these. 


I attached my project so i please help 🙂


After that i have to measure the bioimpedance, thus i have to replace the components and measure the impedance from several points of my skin... but these are next problems....


Best regards

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We have a good amount of information regarding what you are looking for. 

1) Regarding A/D, check out this page:

2) Connecting should be pretty straightforward. Place an indicator on the AO Signals and the AI signals and compare the two. For accurate comparisons, you can subtract the two signals from each other and that will tell you your difference
3) FFT information:

4) Here is a Forum that talks about the analysis of the phase shifts:

5) This page discusses the Angle of Arrival and Phase Compensation:
6) This point I didnt fully understand. 


Douglas Choisnet
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Like I said. I have to calculate the impedance based on the data of impedance and phase. I don't know how to realize that, I have no idea. I guess that i have to know some equation how to do that calculation, because i have to calculate real and imaginary part (reactance and C or L). Aftert that I must connect input and output channel in the configuration for measuring impedance, and I have to connect different resistors, condensators, paralel combinations of resistors and condensators.


7. The next poing is to measure on the different frequencies and getting the frequency characteristics of unknown  impedance. I have to logarithmically change frequency in the range 100 Hz  - 20 kHz, and show amplitude and phase of the impedance as a function of frequency.


8. The last point is to measure bioimpedance. Instead of components, i have to connect one massive electrode (or sheet of aluminium foil) on the one of input channels and one pointy electrode on the second input channel. I have to put massive electrode in my arm and measure bioimpedance on the 10 points  (between thumb and forefinger), on the palm, forearm, upper ar, on the nose and on the top of the ear :))...


Pleaaase help me I have only seven days for realisation..


Best regards

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First thing I would do is go and ask your instructor for an extension. Giving someone who has no idea a week to do something like that without detailed instructions is counterproductive. It gives you not option but to come and ask for the answer on a plate, meaning you learn nothing.

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