Myoware muscle sensor - questions about signal range and filtering

Hello,

I am trying to use Myoware muscle sensor for measuring activity of forearm muscles. It gives out the rectified (SIG) and raw (RAW) signals at the two output pins which I read into the Arduino. Then I use analogRead from two analog pins through the serial port to get it into my Mac (using a baud rate of 500000).

The signals are captured around every 350 microseconds (I don't have a delay in my void loop() in Arduino code). The values for the SIG range from 30-40 to around 900, while the range for the RAW signal is fairly low, from around 450 to around 500.

My questions:

  1. Does the capture rate seem normal?
  2. Are these ranges normal for these two signals?
  3. Do I need to denoise these signals using some type of filter (butter, wavelet etc.), or has it already been passed through a filter in the sensor?

I wanted to know if I can use these signals directly to extract the frequency components using an FFT.

Thanks.

Aakaash

  1. Does the capture rate seem normal?

Your capture rate is unusually high. From my understanding, you should leave a slight delay in your loop so you don’t overload the ADC. By the Nyquist theorem, you really only need a sampling rate of ~1000 Hz.

  1. Are these ranges normal for these two signals?

They seem normal. Magnitudes can change based on what electrodes you’re using, skin prep, how dry your skin is, where you’ve placed the electrodes, etc. The RAW output is centered around Vs/2 and is only amplified by 201x.

  1. Do I need to denoise these signals using some type of filter (butter, wavelet etc.), or has it already been passed through a filter in the sensor?

The SIG output shouldn’t require any further processing. It already has been fullwave rectified and sent through an envelope detector.

The RAW output is simply the input signals amplified by 201x so, if you want to do frequency analysis, you might want to run it through a passband filter with a passband of 10Hz - 500Hz which is the SENIAM standard.

Dear, can you tell me if the MyoWare sensor module has inbuilt 10Hz - 500Hz band pass filter? Or need it separately.

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