Validating emg sensor by Calculating THD

[victow]

Hi, please forgive my poor English.

I'm trying to calculate THD( Total Harmonic Distortion) from the values of emg sensor and arduino board by inputting sine wave(100 Hz, amplitude is 10mVpp) to them. The wiring.jpg(attachment) shows how I connect emg sensor, arduino board and function generator.

My emg sensor is myo ware emg sensor :

MyoWare 2.0 Muscle Sensor - DEV-21265 - SparkFun Electronics

sensor layout is attached.

my board is bluno nano(which is basically like arduino uno) :

Bluno_Nano_SKU_DFR0296-DFRobot

My problem is that the sine wave signal from function generator is too small to be detected by arduino board(A1 pin), I couldn't even get some useful data to calculate THD. I've read some articles on the Net say that maybe arduino is not the ideal option to handle data in such high frequency and low voltage.

Is there a way to allow arduino board to detect such low voltage signal ?
or should I measure SNR(signal-noise ratio) instead of THD for my validation experiment?

Please give me some advise that may be useful!

Thanks!

[Railroader]

Use the internal 1.1 volt reference for A/D. That gives 5 times the resolution.

[johnerrington]

You havent posted your code, please do so.

I think the most significant aspect of measuring the emg will be the rate at which you sample and process the data.

I have a page here on sampling rate - its not enough to use the nyquist criterion.

You would also need to look at the size of the EMG signal as compared to the range of your ADC (ie which reference you use).

You need 10mV from your function generator to drive a "model" signal to the EMG board - but its not big enough to measure with A1.

Also analog inputs can not read AC - the input needs to be between 0V and +Vref

So generate a 0.5V sinewave with a positive 0.5V offfset, and feed to A1:

then divide down with a potential divider 100:1 and capacitor to drive the EMG board.

[johnwasser]

Your function generator output should be in the range of the EMG sensor output.