Simulink - Output 1 every 30 seconds, 0 otherwise

Question

I need a subsystem that needs to output 1 at interval or 30 seconds or slightly over 30 seconds.

Written in matlab code it should work like that

function y = fcn(time,uplinkTimeInterval)

%#codegen

persistent lastTriggerTime

if isempty(lastTriggerTime)

    lastTriggerTime = 0;

end 

if time>=lastTriggerTime || time == 0

    y = 1;

    lastTriggerTime = time + uplinkTimeInterval;
else

    y = 0;

end

end

where ulplinkTimeInterval is 30 seconds. Of course I tried to use the matlab function block with this code but for some reason it does not work (in debug mode I can see that y takes value 1 as it should but it simply does not ouput the value outside the block), therefore I wanted to use blocks but I do not know how to do it.

Thanks very much for your help

Wolfie Wolfie · Accepted Answer · 2017-07-17T13:33:21

You can make this logic relatively easily with code or blocks. As you requested a solution using blocks, here it is!

Use the clock block to keep track of time, and some constant block to determine the interval (in seconds) at which to give 1 instead of 0.
Use the memory block to delay the clock signal by 1 timestep, so we can compare consecutive steps' values.
Divide the times by the interval, and round down, to give how many intervals have passed.
Finally, compare consecutive "number of intervals passed" using a relational operator. If more intervals have passed on the upper line, then you have just stepped over the interval threshold.

Note: this will return a 0 for every timestep where you have not crossed a new interval, and a 1 at each individual timestep where you have. The accuracy of the output will depend on the step size of your model.

Edit: It may be clearer / easier to just add the memory block after the floor block, so you are only doing the division / rounding once. It would still allow you to do a comparison to the previous time step. That would look like:

Simulink - Output 1 every 30 seconds, 0 otherwise

2 Answers