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Data Acquisition, Inaccurate Data From Arduino To MatLab

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Darryl
Darryl on 14 Mar 2013
I have a light sensor running off an Arduino uno board with a resolution of 0 - 100 and a delay of 1000ms after each sample. I am then using the Serial class within MatLab to extract the data in order to plot a graph.
My main concern is that the data doesn't seem as lively and accurate as what it seems to be within the serial monitor window of the Arduino IDE.
Code:
x = [1:60];
for i = 1:length(x)
y(i) = fscanf(ard, '%d');
end
plot(x,y)
Also, after my loop above has executed, it doesnt feel like 60 seconds of data acquisition has passed, so I added pause(1) method:
x = [1:60];
for i = 1:length(x)
pause(1);
y(i) = fscanf(ard, '%d');
end
plot(x,y)
But this made the data capture much more inaccurate, so my main two questions are:
Is there a more efficient way of capturing sensor data, and when using the function fscanf, does it actually take into consideration the delay(1000) method that the Arduino is outputting, or any size delay in fact?

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Answers (1)

Walter Roberson
Walter Roberson on 15 Mar 2013
fscanf() is going to wait for the line terminator in each case. You should not need the pause() at all.
Could you explain more about "lively and accurate" ?

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Darryl
Darryl on 15 Mar 2013
Thank you for the reply. Sorry, I'll elaborate some more..
Well, when its running through the serial monitor (Arduino IDE), it seems very responsive when moving my hand over the sensor and pointing it at my desktop light, etc.
When I run the fscanf method, there is definitely a long delay, but I wouldn't say 60 seconds. Whilst the method is capturing the data (MatLab prompts busy), and I manipulate the sensor the same way as above, the graph output just doesn't quite seem as it should. For example, I'll get large spikes and flat lining thats either above or below what the serial monitor (Arduino IDE) prints.
I'll attach a picture to demonstrate.

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