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How can I fix my rolling plot of Matlab Mobile's accelerometer?

Asked by Anthony Beckner on 14 Aug 2015
Latest activity Answered by James Wiken on 17 Aug 2015
So, I am using Matlab Mobile to try and make a rolling plot that updates with the z axis of the accelerometer data from my android phone. I connected correctly and have written this code which works:
%connect to phone and get accel data
clear m
m = mobiledev;
m.AccelerationSensorEnabled = 1;
m.Logging = 1;
%initialize data for rolling plot
data = zeros(1,200);
tic
while (toc < 30)%run for 30 secs
%read from accel
a = m.Acceleration;
%conditional prevents it from indexing an empty array the first couple
%of times
if(exist('a','var')&&~isempty(a))
%get new z coordinate
newPoint = a(3);
%concatenate and pop oldest point off
data = [data(2:length(data)) newPoint];
%draw plot with set axes
plot(data);
axis([0 200 -15 15]);
drawnow
end
end
My problem is that the resulting rolling plot doesn't resample the data quick enough for what I want. It results in a stepfunction that updates every second or so. Is there anyway to make it resample faster or is this simply due to the nature of the matlab mobile wifi connection? If so, is it possible to connect with bluetooth or some other method such that matlab gets updated points more frequently?

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1 Answer

Answer by James Wiken on 17 Aug 2015
 Accepted Answer

You can improve the sample rate for your rolling plot by using the 'accellog' function, similar to the example seen here:
The following code is a modification of your provided code using this function. The resulting plot has a update rate of about 1 Hz with a data sample rate of about 10 Hz. It does provide a smoother looking plot, but it still has the relatively slow update to the plot. Further increasing the rate of either the sample rate or the update rate seems to be a current limitation for MATLAB Mobile.
%connect to phone and get accel data
clear m
m = mobiledev;
m.AccelerationSensorEnabled = 1;
m.Logging = 1;
%initialize data for rolling plot
data = zeros(200,1);
%initialize plot
figure(1)
p = plot(data);
axis([0 200 -15 15]);
pause(1)
tic
while (toc < 30)%run for 30 secs
%get new z coordinates
[a,~] = accellog(m);
if length(a) > 200
data = a(end-199:end,3);
else
data(1:length(a)) = a(:,3);
end
% redraw plot
p.YData = data;
drawnow
end
Example Plot:

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