find the start point of abrupt change in signal matlab

Hello,

I have a signal as y = [x y sh oa ahdv ...] and looks like as below:

I need to find the the point where signal increased abruptly and tried diff(), findchangepts(), ischange(), etc but any of them did not help me. I have 100 sample looks like this data so I am looking for a function that can do this job automatically.

I would be very grateful if anyone could help me.

Thanks.

Demet

[Chunru]

Attach your data.

[Demet]

Hello,

Here is a data sample attached.

Thanks.

Answer 1

[Chunru]

load triggerInput.mat
plot(trigger)

trigger = trigger(1:2e4);       % select the 1st part

%xlim([1 1e4])
%xlim([1500 2500])
% low pass the signal
%{
b = fir1(128, 0.001);
y = filtfilt(b, 1, trigger);

ipt = findchangepts(y,'MaxNumChanges',2)


yd = diff(y);
idx = find(yd>3e-3, 1, 'first')

figure
hold on
plot(y)
plot(trigger, 'r:');
xline(ipt, 'g');
grid on; box on
xlim([1 2e4])
fprintf('The change point at %d\n', ipt(2))
%}

Update based on your new explanation:

b = fir1(128, 0.001, 'high');
y = filtfilt(b, 1, trigger);

ipt = findchangepts(y,'Statistic', 'rms', 'MaxNumChanges',2)

ipt = 1×2

1733 7865

figure
hold on
plot(y)
plot(trigger, 'r:');
xline(ipt, 'g');
grid on; box on
xlim([1 2e4])

[Demet]

Hello,

First of all, thank you for your code.

However, the point(or points) you found are not the one I want them to find. I also used findchangepts(y,'MaxNumChanges',2(or 3,4,5 etc.)), but it does not help me to find the point I want to detect.

I have attached two images to show you exactly which the point I need to find looks like, if you could help I'd be very grateful. I also accept your answer to thank you for your time so far.

Here is a picture of what this software finds and the points I want to find:

Zoomed in on the point I want to find:

Thanks,

Demet

[Chunru]

See the update

[Demet]

Hello,

I have checked the update and it works almost well. I have checked for each data and I decide to continue with this program as the maximum error is 30 for the sampling frequency is 512 (30/512=0.57 s).

Thank you!