Hi, I want 2 timer objects to execute sequentially, one after the other. Please help

Question

Mitra Bapat on 2 Mar 2015

1

Commented: Mitra Bapat on 6 Mar 2015

Suppose my program is as follows:

t = timer;
t.StartDelay = 3;
t.TimerFcn = @(myTimerObj, thisEvent)disp('hello');
start(t);
t1 = timer;
t1.StartDelay = 5;
t1.TimerFcn = @(myTimerObj, thisEvent)disp('world');
start(t1);

I want my program to display 'hello' after 3 seconds, which it does. But it displays 'world' 2 seconds after 'hello' is displayed. i.e. simultaneous execution takes place.

I want 'world' to be displayed 5 seconds after 'hello' is displayed. And making the delay 8 is not the answer I'm looking for! I need sequential execution because I want to put it in an infinite loop.

It should display 'hello' after 3 seconds, and 5 seconds later 'world'. Then 3 more seconds later 'hello' should be displayed, and 5 seconds after that, 'world'. This is needed in an infinite loop.

Please help

Thank you!

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Answer 1

Oleg Komarov on 2 Mar 2015

2
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https://www.mathworks.com/matlabcentral/answers/181079-hi-i-want-2-timer-objects-to-execute-sequentially-one-after-the-other-please-help#answer_169866

Edited: Oleg Komarov on 2 Mar 2015

You can use one timer and a function that alternate the state(s):

tic
t = timer;
t.ExecutionMode = 'fixedDelay';
t.StartDelay    = 3;
t.TimerFcn      = @(obj,evt) alternateState(obj);
start(t);
% After you are done
stop(t)
clear persistent

And the state alternation is done by:

function alternateState(t)
persistent on
if isempty(on)
    on = true;
end
toc
stop(t)
if on
    disp('hello')
    t.StartDelay = 5;
    on = false;
else
    disp('world')
    t.StartDelay = 3;
    on = true;
end
start(t)
end

The state persists within the scope of the function.

Basically, you start the timer on repeated execution with fixed delay, and initial delay of 3. When the first time the function fires, it initializes the state to 'on', prints 'hello', sets the next delay to 5. On the next call, it reverts the delay back and prints 'world'.

Note, I am not sure this is clean, and would appreciate feedback, but it has the advantage to support several states. You can also clean away the tic/toc which is there for debugging purposes.