# display gait cycle in matlab

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NGR MNFD on 30 Sep 2021
Commented: Mathieu NOE on 4 Oct 2021
Hello friends
I have a diagram of the walking gait signal related to the left and right force signal feet of people. This signal is measured by an analog to digital converter 12 bit , so the vertical axis of this diagram is in terms of voltage and the horizontal axis is in terms of the number of samples. Now I want to know how I can change the vertical axis from voltage to force(m/s^2)? (Through what code in MATLAB?)
I use this code for display signal for neurodegenerative disease in physionet site:
fileID1=fopen('control1.let','r');
A= fread(fileID1, [3, 45000], 'uint8')'; % matrix with 3 rows, each 8 bits long, = 2*12bit
fclose(fileID1);
M2H= bitshift(A(:,2), -4);
M1H= bitand(A(:,2), 15);
PRL=bitshift(bitand(A(:,2),8),9); % sign-bit
PRR=bitshift(bitand(A(:,2),128),5); % sign-bit
M( : , 1)= bitshift(M1H,8)+ A(:,1)-PRL;
M( : , 2)= bitshift(M2H,8)+ A(:,3)-PRR;
N1 = reshape(M',[90000,1]);
subplot(2,4,1);plot(N1);title('Healthy control'); ylabel('left force');

Mathieu NOE on 30 Sep 2021
hello
this is not really a matlab question ...
you have to know the sensivity of the sensor - whatever you measure , you need that info to go from measurement (voltage) to physical units. pay also attention to any device that modify the gain of the acquisition chain (signal amplifiers, ADC gain and so forth)
NB : m/s² is the unit of acceleration, not force (Newtons or pounds or ...)
at the end , it's just a gain factor to apply on your y data
Mathieu NOE on 4 Oct 2021
My pleasure !

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