How to use 'Timer' function to send ROS messages?

fps=50;

How can send ROS messages through a publisher continuously.

Answer 1

[Koundinya]

You can use MATLAB timers in this way :

% Create a timer object
 t=timer;

Set execution mode of the timer object to fixedRate, fixedDelay or fixedSpacing to execute your call back repeatedly

 set(t,'executionMode','fixedRate');

Specify the function handle or the command you want to be executed. In your case, for sending messages over a ROS topic , use send :

set(t,'TimerFcn','send(pub,msg)');

Set the frequency or period(in seconds),at which the timer callback function is called

% To publish the message at a rate of 50 times per second 
set(t,'Period', 0.02);

% Start the timer
start(t);

ROS message msg is then sent periodically(every 0.02 seconds). To stop the timer:

stop(t);

Delete the timer object after usage

delete(t);

[JAI PRAKASH]

Thanks @Poluri

If 'msg' is varying with time then?

[Koundinya]

Then you can include the code that generates/modifies msg in a function, and pass it to the timer object :

set(t,'TimerFcn',@sendROSMessage);

function sendROSMessage(obj, event)
% modify msg
% msg=getSensorReading();
% msg=msg+1;

% send
send(pub,msg); 
end

Refer to the documentation on MATLAB timer callback functions for more details

[JAI PRAKASH]

msg.Data=getSensorReading();

[Arun Prasanth Soungyan Gokul]

Hi Koundinya,

I'm trying to use the timer object which you suggested. I already created the publisher and it's respective message(pub,msg). But when I set set(t,'TimerFcn','send(pub,msg)'), and the other attributes

and run start(t); it says undefined function or variable msg,undefined function or variable pub.

Can you please help me out from this?

[Koundinya]

Hi Arun,

You need to first create a ROS publisher object(named 'pub' in this case) and then define a message ('msg') that is to be published. Take a look at the documentation of rospublisher and send for examples.