Serial communication with timer

Hi all

I want to control a external device over a serial connection. I have two 1000-element arrays in matlab with the positions to send. When I just use a for loop to send the data, then the whole array is sent in about 3 seconds. This is too fast, I just want to send one position every 10ms so that the whole process takes 10 seconds. When I add a pause(X) after sending one position, then the whole process takes about 16 seconds, and it doesn't matter if I enter 0.01 or 0.0001 as X. Why is that?

Then I tried to use a timer. But I couldn't figure out how to write the TimerFcn that it works.

Can someone help me? The beginning would be as follows.

PositionX = rand(1,1000);
PositionY = rand(1,1000);

T=timer('Period',0.01,'TasksToExecute', 1000)
T.ExecutionMode='fixedRate';
T.TimerFcn = %%insert function here %%
start(T);

What the function should do is the following:

fprintf(serial_object,PositionX(i));
fprintf(serial_object,PositionY(i));

as i goes from 1 to 1000.

Best regards and thanks for the help,

Reto

[Walter Roberson]

I notice you are not using a format when you fprintf(). If I recall correctly, the default format is '%s\n' which is not going to work well with your numeric data. You should provide a specific format. Also for efficiency, use a single fprintf() instead of two in a row, something like

fprintf(serial_object, '%9.3f %9.3f\n', PositionX(i), PositionY(i))

[Reto Hofmann]

Hey thank you for your comment. I couldn't yet test the part with the timer but I tried to implement the part with the specific format.

In each step I have to send 4 numbers in the range from 0-255, which are 4 byte. When I make it like that,

mynumber=[32, 56, 36, 55]; fprintf(s, '%c', mynumber)

then it works. The problem is, if there is a 0 in the mynumber vector, then it only transmits the numbers up to that 0. How do I send a 0?

[Walter Roberson]

fwrite(s, mynumber, '=>uint8')

Answer 1

[Walter Roberson]

T.TimerFcn = setup_timer();

function timerfcn = setup_timer
  i = 0;
  timefcn = @send_position;

    function send_position(varargin)
      i = i + 1;
      if i <= length(PositionX)
        fprintf(serial_object, '%9.3f %9.3f\n', PositionX(i), PositionY(i))
      end
    end

end