How to isolate one pulse from a periodic pulse train

I want to isolate on pulse from this waveform, the data is in a CSV file and the 2 columns contain time data and voltage data.

I want to use a MATLAB code to trim out one full pulse (+peak,zero,-peak,zero)

How can I do this, the peak value is shown using the data cursor

[KALYAN ACHARJYA]

Use voltage>upper_th & voltage<lower_th??

[Hans123]

If you can, can you explain a little further. I need only one pulse out of the 3 in the image. How can I isolate one pulse?

Answer 1

[Star Strider]

One approach:

t = linspace(0, 2.3, 500);                                                          % Time Vector
pulses = -0.14*sign(sin(5*pi*t/2).*(abs(sin(5*pi*t/2))>0.9)) + rand(size(t))*0.005; % Create Waveform

Mv = pulses > 0.1;                                                                  % Threshold
Mvs = strfind(Mv, [0 1]);                                                           % Start Of Each Pulse
Mve = strfind(Mv, [1 0])+1;                                                         % End Of Each Pulse

figure
plot(t, pulses)
hold on
plot(t(Mvs(1):Mve(1)), pulses(Mvs(1):Mve(1)), '+')
hold off

Make appropriate changes to work with your signal.

[Hans123]

Hi Star Strider, thanks for the Answer - it works but I am having trouble adapting it to my code. Do you mind explaining me how these three lines work. I am relatively new here and have not used the string find command

Mv = pulses > 0.1;                                                                  % Threshold
Mvs = strfind(Mv, [0 1]);                                                           % Start Of Each Pulse
Mve = strfind(Mv, [1 0])+1;  

[Star Strider]

My pleasure.

The ‘Mv’ assignment that simply finds values of the function greater than 0.1, and returns a logical vector.

In:

Mvs = strfind(Mv, [0 1]);                                                           % Start Of Each Pulse
Mve = strfind(Mv, [1 0])+1;  

the ‘Mvs’ and ‘Mve’ assignments detect the beginning and end (respectively) of the pulse by detecting the transition from and in that vector. The use of the strfind function in this context is not at all intuitive, since none oif the arguments are actually strings. It simply works in this context, and is frequently used to find specific sequences in logical vectors.

An equivalent implementation using find and diff would be:

Mvs = find(diff([Mv(1) Mv]) > 0)-1
Mve = find(diff([Mv(1) Mv]) < 0)

The strfind versions are simpler, more efficient, and more flexible in general terms, in that strfind can be used to detect more complex patterns, avoiding more complicated code.

[Hans123]

Thanks a lot, I really appreciate your help!

[Star Strider]

As always, my pleasure!