Multiple Y variables in RealTime

I am attempting to read multiple variables from an arduino and plot in real time. The data is from an gyroscope so I have 3 Axis data so am trying to plot all three Y variables. I am using the following code:

s = serial('COM4', 'baudrate', 115200);

plotTitle='Gryoscope';

xLabel='Time (s)';

yLabel='Distance';

plotGrid = 'on';

delay = .01;

time = 0;

distance1 = 0;

count = 0;

plotGraph = plot(time,distance1);

grid(plotGrid);

fopen(s);

tic

while ishandle(plotGraph)

dist = str2num(fscanf(s))

count = count + 1;

time(count) = toc;

distance1(1,count) = dist(1);

distance1(2,count) = dist(2);

distance1(3,count) = dist(3);

set(plotGraph(1),'XData',time,'YData', distance1);

axis([time(count)-10 time(count) 0 10]);

pause(delay);

end

I get an error at "set(plotGraph(1),'XData',time,'YData', distance1);" as distance1 variable is too large. I have tried converting to cell variable and plotting separately with hold on but neither are working. Is there any way to overcome this to plot both Y variables on the same graph in real time?

Answer 1

[Neuropragmatist]

If you mean that distance1 has too many elements to be plotted you could just downsample it - i.e. by taking every 10th or 100th point instead of every point. But that seems unlikely because Matlab can plot a lot of data points.

If you mean that distance1 doesn't match the size of 'time', then I don't know why that would be the case.

What is the error you get specifically?

[Andrew Mason]

I thought it was a case of distance1 doesn't match the size of 'time' as there are two variables in there but I had another look and I dont think its that

The error I get is:

'Error using matlab.graphics.chart.primitive.Line/set

Value must be a vector of numeric type

Error in SerialPortRead (line 132)

set(plotGraphx(1),'XData',time,'YData',distance1);'

Answer 2

[Steven Lord]

distance1 is not a vector, it is a matrix.

If you're plotting one line in your call the plot and want to update it with the latest vector stored in distance1, set the YData to distance1(:, count) rather than the entire distance1 matrix.

If you're plotting multiple lines with one call to plot, the output from plot will be a vector of line handles. You can't set the YData property of that vector to a matrix the way you're trying to. You'll need to either set the properties of each element of the vector of line handles individually or use a cell array.

h = plot((1:10).', rand(10, 3)) % h is 3-by-1
for iteration = 1:10
    newYData = {rand(1, 10); rand(1, 10); rand(1, 10)}; % You could use mat2cell here
    set(h, {'YData'}, newYData)
    
    pause(1) % So you can see the change
end