AHRS on Matlab lengths error

Hello to everyone,

A part of my thesis is to build an AHRS in matlab but when I'm trying to plot some data, from a gyroscope connected to arduino, in matlab, i'm getting the following error

??? Error using ==> plot Vectors must be the same lengths.

Error in ==> serialread at 14

plot(counterz,y(data));

Here is my code

    function serialread(zaxis)

y=zeros(1,1000);
s=serial('COM1');
fopen(s);

counterz=1;

while counterz<=zaxis
    ylim([-150 150]);
data=fscanf(s,'%s');
%y(data)=(data)*5/1024;
plot(counterz,y(data));
drawnow
counterz=counterz+1;

end

fclose(s);
delete(s);
clear all;

end

What am i doing wrong?

the code on arduino is this

#include <Wire.h>
#include <L3G.h>

L3G gyro;

void setup() {
  Serial.begin(9600);
  Wire.begin();

    if (!gyro.init())
    {
      Serial.println("Failed to autodetect gyro type!");
      while (1);
    }

    gyro.enableDefault();
  }

void loop() {
  gyro.read();

    Serial.println((int)gyro.g.z);

    delay(100);
  }

Thanks alot in advance,

Minas

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/matlab/ref/fscanf.html

The fscanf function reapplies the format throughout the entire file, and positions the file pointer at the end-of-file marker.

So you are reading in all of the strings in the file and assigning that to a variable, where it will become a row vector of characters.

Then you are plot(counterz, y(data)). You index an array y() at the row vector of characters, getting one result per character. But counterz is a scalar.

You probably want to read with a numeric format such as '%d' or '%f' rather than with a string format '%s'. And you probably only want to read one value at a time; consult the fscanf() documentation for how to do that. Lastly, you are probably going to want to have a "hold on" unless you just want to display one point, erasing all the others when plot() is called again.

Answer 2

[Minas]

Thank you alot for you help. It cleared some missunderstanding i had in the fscaf command. So here comes my second question.

I want to read serially from arduino this sequence of numbers -242 42 154 which with a delay of .5 second refreshes and i get the next and the next. I want to read it on matlab so i have to use fscanf.

There are 3 different numbers with a range of -300 to 300 lets say and i seperate these 3 numbers with spaces. How can i read them with fscanf? Im trying this fscanf('%d %d %d') is that correct?

Than you again for your help

[Walter Roberson]

fscanf(s, '%d %d %d', 1)

Answer 3

[Minas]

Ah nice!

I'v reached something here. I manage to get one dot inside my plot with the following error

A timeout occurred before the Terminator was reached or SIZE values were available.

Thank you alot for the tip. that solved the previous error.

What i want to do is to plot for 500 fractions of time the data i recieve. so i'm using this code;

function serialread(zaxis)

y=zeros(1,1000);
s=serial('COM3');
fopen(s);

counterz=1;

while counterz<=zaxis
    ylim([-150 150]);
data=fscanf(s, '%d %d %d', 1);
plot(counterz,data);
drawnow
counterz=counterz+1;

end

fclose(s);
delete(s);
clear all;

end

On matlab's conmmand line i just write seriealread(500) But every like 10 seconds matlab freezes and after it i get a plot with a spot in the middle and the y axis increased by one.

Any suggestions on that one?

Thank you alot for your help

Minas