Determine the start and end of a vector.

When the variable starts incrementing above a threshold, that index is to be determined and also when the same variable starts decrementing below a certain threshold, the index is to be determined.

[Walter Roberson]

Are the two thresholds the same value?

[Ferd]

Two different thresholds

Answer 1

[Image Analyst]

Try using diff() and strfind():

% Create random sample data.
v = randi(9, 1, 20)
thresh = 3; % Define the threshold.
% Find indexes where v is at or above the threshold.
d = (v>=thresh)
% Find the starting index where the signal starts above the threshold
% and then starts to fall below the threshold.
fallsBelow = strfind(d, [1, 0])
% Find the starting index where the signal starts below the threshold
% and then starts to rise above the threshold.
risesAbove = strfind(d, [0, 1])

[Walter Roberson]

This is a good approach when the thresholds are the same. Matters get more complicated when the thresholds are different. For example if you wanted to trigger at 1/4 Volt and to keep monitoring until you dropped to 0 V, then it becomes trickier.

[Ferd]

Thanks! Yeah, had just set it up with two separate thresholds, d1 and d2. Its giving the results I'm looking for!