Maximum code
I want to calculate if the signal in real time is transmitting some thresholds in the first step. In the first step, I want to determine if a real signal passes below these thresholds (to detect a peak in the signal). My Matlab code:
k=1;
t = 1;
l=1;
for i =1:length(sm) //sm my signal.
if (sm(i) > 0.25)
first(k) = i;
k = k+1;
if (sm(i) > 0.5)
second(t) = i;
t =t +1;
if (sm(i) > 0.75)
third(l) = i;
l = l+1;
end
end
end
end
Example:
! [enter image description here] [1]
I want to calculate the time of the signal and under three rapids 0.25
, 0.5
, 0.75
and return these windows. Basically the three main peaks I have in my example.
Basically what I'm trying to do is use fastsmooth and findpeaks function.
signalSmoothed = fastsmooth(sm,50); plot(signalSmoothed) [max_pk1 max_pk2] = findpeaks(signalSmoothed); find(max_pk1 >0.5) inversex = 1.01*max(signalSmoothed) - signalSmoothed; [min_pk1 min_pk2] = findpeaks(inversex); find(min_pk1 >0.5)
What are the heuristics to take only the peaks you want? In addition, the depicting image is a stand-alone example. I usually want to do the technique online.
EDIT: I am mistakenly defined as the peak of my desired curve result, which represents the whole wave, not just the maximum value.
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Here is a solution to get the points where the signal sm
passes the thresholds of 0.25, 0.50 and 0.75. Points can be converted to windows within a data range and saved to W
. Finally, we can easily plot them in the same figure. Note that we need to do some checks in the local function getwindows
to handle special cases, such as when the window is out of data range. Detecting windows inside another window is done in the getwindowsspecial
-function.
Here is the code:
function peakwindow
% generate sample data
rng(7);
sm = 2*rand(1,25)-0.5;
sm = interp1(1:length(sm),sm,1:0.01:100*length(sm));
% get points
firstup = find(diff(sm > 0.25)==1);
secondup = find(diff(sm > 0.50)==1);
thirdup = find(diff(sm > 0.75)==1);
firstdown = find(diff(sm < 0.25)==1);
seconddown = find(diff(sm < 0.50)==1);
thirddown = find(diff(sm < 0.75)==1);
% plot the result
figure; hold on;
plot(sm,'k')
plot(firstup,sm(firstup),'*')
plot(firstdown,sm(firstdown),'*')
plot(secondup,sm(secondup),'*')
plot(seconddown,sm(seconddown),'*')
plot(thirdup,sm(thirdup),'*')
plot(thirddown,sm(thirddown),'*')
% get windows
W1 = getwindows(firstup,firstdown);
W2 = getwindows(secondup,seconddown);
W3 = getwindows(thirdup,thirddown);
% get special window
WS = getwindowsspecial(W1,W3);
% plot windows
plotwindow(W1,0.25,'r');
plotwindow(W2,0.50,'r');
plotwindow(W3,0.75,'r');
plotwindow(WS,0,'b-');
function W = getwindows(up,down)
if length(up)>1 && length(down)>1 && up(1)>down(1)
down(1)=[]; % handle case when window begins out of bounds left
end
if length(up)<1 || length(down)<1;
W = []; % handle if no complete window present
else
% concatenate and handle case when a window ends out of bounds right
W = [up(1:length(down));down]';
end
function plotwindow(W,y,lspec)
for i = 1:size(W,1)
plot(W(i,:),[y,y],lspec)
end
% get windows of U where there is a window of H inside
function W = getwindowsspecial(U,H)
W = []; % empty matrix to begin with
for i = 1:size(U,1) % for all windows in U
if any(H(:,1)>=U(i,1) & H(:,1)<=U(i,2))
W = [W;U(i,:)]; % add window
end
end
This is the result:
To ensure that the processing is working correctly, we can plot the result on initialization with rng(3)
:
Please note that the window with 0.25 and 0.50 will start to leave the borders on the left and, therefore, is absent in the constructed windows.
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