Robust edge/flank detection - HELP!!

Hey guys,

i have an measurement and read in three rect. signals.

I need to detect the pos. and neg. edges/flanks of the three signals.

Sometimes I have the problem that my code doesnt detect all flanks/edges and i dont know why.

In the attachment u find a pictures with with all three signals and the detected signals but not all are right.

I counted them by hand:

left Signal -> 28 pos. and 27 neg.

middle Signal -> 27 pos and 27 neg (this signal is ok)

right signal -> 27 pos and 27 neg

So if u compare it only the middle one is correct.

My Code for that detection is:

            posFlankHall_1 = find(diff(V_Hall_1)>1.6)+1;
            negFlankHall_1 = find(diff(V_Hall_1)<-1)+1;
            
            posFlankHall_1OrigLength = length(posFlankHall_1);
            negFlankHall_1OrigLength = length(negFlankHall_1);
            
            posFlankHall_2 = find(diff(V_Hall_2)>1.6)+1;
            negFlankHall_2 = find(diff(V_Hall_2)<-1)+1;
            
            posFlankHall_2OrigLength = length(posFlankHall_2);
            negFlankHall_2OrigLength = length(negFlankHall_2);
            
            posFlankHall_3 = find(diff(V_Hall_3)>1.6)+1;
            negFlankHall_3 = find(diff(V_Hall_3)<-1)+1;
            
            posFlankHall_3OrigLength = length(posFlankHall_3);
            negFlankHall_3OrigLength = length(negFlankHall_3);

I have three question to that:

1) Is there maby a easier and more robust way to detect the flanks/edges?

2) How can I automatically find out the values (like in this case 1.6 and -1) so i can use it on every signal i read in

3) If there is no easier way is there a way to improve this one?

Thank you very much in advance.

[Star Strider]

See also: Repeating x-axis for rectangular signal

Answer 1

[Star Strider]

See if the midcross (link) function will do what you want.

I would have suggested this earlier, however even though it has been part of the Signal Processing Toolbox since R2012a, I just now discovered it.

[youjarr]

Hey Star Strider,

i cannot use this command.

i get this error:

Error using midcross (line 65)

Expected X to be one of these types:

double

Instead its type was single.

[Star Strider]

That is not mentioned in the documentation.

Try this:

C = midcross(double(X))

If you pass any other arguments to it, double() them as well.

Also, note the related functions at the end of that documentation page.