How can I (for a digital signal) estimate the interval between steps of amplitude 1?

I have a footswitch signal that when is active it gives 1 and when is deactivated delivers 0 sampled every 1 ms; I want to estimate how long is the interval between each step (from the instant when the switch is activated). Considering that only the steps with a duration longer than 5 ms are acceptables. The size of the interval is recorded at the corresponding column of a "vector". For that purpose I´ve developed the code:

for ii=1 : length(vector)

   for jj=step : length(footswitch) %Go around the vector of the signal footswitch
    while footswitch(jj)==1   
       if jj < length(footswitch)-4
        if footswitch(jj)==footswitch(jj+1)==footswitch(jj+2)==footswitch(jj+3)==footswitch(jj+4)==1
            k=jj;
            if footswitch(k)==1
                steps=k+1;
            end
         end    
       end
    end   
   end

    for aa=steps : length(footswitch)
      while footswitch(jj)==0  
         p=aa;
         if footswitch(p)==0
            stepss=p+1;
         end
      end   
    end   

    intervalo=stepss;
    vector(ii)=intervalo;
end

Can anyone tell me what is wrong with the code? I've tested it and it gives me a wrong estimation for the first interval and then it just go worse!

Answer 1

[W. Owen Brimijoin]

The code you've included doesn't work because we don't know what the variable 'step' is defined as. You might have more luck first using 'diff' to find the time points when your signal goes from 0 to 1. Formally speaking, this is when the first derivative is equal to +1

idx = find(diff(footswitch)==1);

Then you can measure how far apart these indices are (again with 'diff') and use this to get rid of instances that are too close together in time (i.e., that have a first derivative less than or equal to 5 ms).

idx(find(diff(idx)<=5)+1) = [];

This may work better for you and has the benefit of being easier to follow than nested 'if' and 'while' loops.

[Héctor]

thank you for your advice, I will try to implement your solution!