MATLAB: How to apply moving average filter for continious strem of incomming data

moving average filter

i am having accelerometer and i am getting its x,y and z axis values(in g units) continuously from the serial port. i need to filter/smooth-en the incoming data. so i want to apply moving average filter/Savitzky-Golay smoothing filters.. how can i do it?. In http://in.mathworks.com/help/matlab/data_analysis/filtering-data.html they took an 24×3 array.. but in my case array size is not known or it keeps on increasing.. so how to solve this problem?

Best Answer

To do real-time filtering, you need the DSP System Toolbox. You probably also need specialised hardware. (I have no experience with the DSP System Toolbox, so I cannot help you with it.)

I seriously doubt that you could do a Savitzky-Golay filter in real time. Instead, save your raw signals and process them later. You will need to do a fft on your saved signals, determine the frequencies of the signals and the frequencies of the noise, then design a bandpass filter to eliminate the d-c offset and slow baseline drift on the low end, and noise at the high end. You cannot eliminate broadband noise with a frequency selective filter, so some noise will remain after the filtering process.

My filter design procecure is here: How to design a lowpass filter for ocean wave data in Matlab?

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MATLAB: Fir and iir filtering

You have to know your filter specifications. If you do, you can do both with fdesign.lowpass and fdesign.highpass

fdesign.lowpass and fdesign.highpass have different specification strings which support different filter designs.

The default string 'Fp,Fst,Ap,Ast' supports both FIR and IIR designs.

Here is an example:

Design a lowpass filter with a passband frequency of 1 kHz, a stopband frequency of 1.5 kHz, passband ripple of 0.5 dB, and stopband attenuation of 40 dB. The sampling frequency is 20 kHz

   d = fdesign.lowpass('Fp,Fst,Ap,Ast',1e3,1.5e3,0.5,40,20e3);
   designmethods(d)  %shows which designs are valid for this spec
   Hdeq = design(d,'equiripple'); % FIR filter
   Hbutt = design(d,'butter'); %IIR design

MATLAB: Plotting continious-time signal

That's correct. You plotted three signals, with angular frequency of pi, 3/2*pi, and 2*pi rad/s. This corresponds to frequency of 0.5, 0.75, and 1 Hz.

Note, you might want to make increment t using a smaller step size, so the plots are smoother. Try:

t = 0:0.001:10;

Best Answer

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MATLAB: Fir and iir filtering

MATLAB: Plotting continious-time signal

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