How to on/off a variable after 3 seconds interval

I have a small project with Raspberry pi.

I would like to turn the on/off the LED after every 3 seconds. if the time is 90 seconds then the simulation would stop.

Note: I would like to program it in Matlab first, then I will convert it into C++ which is suitable for Raspberry pi.

I am not sure about this below written systax. I can not count the 90 seconds. should I use a timer? Should I use Stateflow or Matlab scripts?

led1=0;  % initially the LED is off
aa=repmat(3,1,30); % I dont know how to initilize this 3 seconds
% aa=3:3:90
for i=aa
    pause(i) % wait for 3 seconds
    led1=1;  % after 3 seconds LED is On
    pause(i) % wait for 3 seconds
    led1=0;  % then after 3 seconds LED is Off
    % continue this process upto 90 seconds.
end

Answer 1

[DUY Nguyen]

Hi ismat,

You could use timer for more precise control of the LED.

However, for simple application, you can use pause() in Matlab (or Sleep() in C++,). There will be a small milli-seconds of the interval depends the code runtime. Matlab scripts works well for this.

You can store your led_value in this variable led_results. You can look at the example code below in Matlab:

led1 = 0; % initially the LED is off
t = 0; % initialize time to zero
dt = 1; % time step size in seconds
stop_time = 9; % stop time in seconds
led_time=3;
% preallocate array to store LED results
led_results = zeros(1, stop_time/led_time);

% loop until stop time is reached
while t < stop_time
    % wait for 3 seconds
    pause(led_time)
    
    % turn LED on
    led1 = 1;
    led_results(floor(t/led_time)+1) = led1; % store LED result
    
    % wait for 3 seconds
    pause(led_time)
    
    % turn LED off
    led1 = 0;
    led_results(floor(t/led_time)+2) = led1; % store LED result
    
    % increment time
    t = t + 2*led_time;
end

% display LED results
disp(led_results)

[Ismat]

when stop_time = 12, the output is 1 0 1 0 which is correct

but, when stop_time = 15, the output is 1 0 1 0 1 0 which is wrong. the output should be 1 0 1 0 1

[Ismat]

possibly i solved it. just need a break statement

led1 = 0; % initially the LED is off
t = 0; % initialize time to zero
dt = 1; % time step size in seconds
stop_time = 9; % stop time in seconds
led_time=3;
% preallocate array to store LED results
led_results = zeros(1, stop_time/led_time);
% loop until stop time is reached
while t < stop_time
    % wait for 3 seconds
    pause(led_time)
    
    % turn LED on
    led1 = 1;
    led_results(floor(t/led_time)+1) = led1; % store LED result
    if t==stop_time-3
        break
    end
    
    % wait for 3 seconds
    pause(led_time)
    
    % turn LED off
    led1 = 0;
    led_results(floor(t/led_time)+2) = led1; % store LED result
    
    % increment time
    t = t + 2*led_time;
end
% display LED results
disp(led_results)

[DUY Nguyen]

yes, that works well!

Answer 2

[VBBV]

led1=0;  
aa=3; 
tic
T = toc
while T<=90
    pause(3);
    led1=1;  
    pause(3); 
    led1=0;  toc;
  T = toc; 
end
%disp("The time lapsed is"+toc)

You can modify as above

[Ismat]

If the stop time is 9 seconds, then I got this result. in my project seconds means real-time seconds. it would be an integer rather than a float.

Elapsed time is 0.000022 seconds.
Elapsed time is 6.019863 seconds.
Elapsed time is 12.033531 seconds.

Actually, I can not verify this code right now. is it possible to store the led1 result?

for example for 9 seconds the result would be:

0 1 0 1

led1=0;  
aa=3; 
tic
toc
while toc<=9
    pause(3);
    led1=1;  
    pause(3); 
    led1=0;  
  toc
end

[VBBV]

Yes, it is possible to store the results of led1 inside loop as

 i = 1;
while T<=90
  pause(3) 
  led1 = 1;
  L(i) = led1;
  pause(3) 
  led1 = 0
  L(i+1) = led1;
  i = i+2;T = toc;
end

[Ismat]

I executed the code. It could not show the expected output.

when T=9, output would be 1 0 1

when T=12, output would be 1 0 1 0

[VBBV]

Below is the modified code, which works according to the output you need

clear all  % very important to run this line, otherwise displays incorrect results
led1 = 0;
aa=3; 
tic
T = toc;
i = 1;
while T<90
    pause(3)    
    led1 = 1;
    T = floor(toc);
    disp("The time lapsed is " +  T +   "seconds")
    L(i) = led1;
    disp("The timer ON/OFF sequence is ")
    L
    pause(3) 
    led1 = 0;
    T = floor(toc);
    disp("The time lapsed is " +  T +   "seconds")
    L(i+1) = led1;
    disp("The timer ON/OFF sequence is ")
    L
    i = i+2;
    T = floor(toc);    
end 
>> The time lapsed is 3seconds
The timer ON/OFF sequence is 

L =

     1

The time lapsed is 6seconds
The timer ON/OFF sequence is 

L =

     1     0

The time lapsed is 9seconds
The timer ON/OFF sequence is 

L =

     1     0     1

The time lapsed is 12seconds
The timer ON/OFF sequence is 

L =

     1     0     1     0

Answer 3

[Prasanth Sunkara]

Hi Ismat,

Simulink is an ideal platform for your project. Simulink offers time based simulations and you can generate C/C++ code easily from the model and deploy it to Raspberry Pi. Please feel free to check out the Simulink Support package for Raspberry Pi Hardware.

Also check out this basic LED example. You can chage the pulse duration and duty cycle to meet your use case. https://mathworks.com/help/supportpkg/raspberrypi/ref/getting-started-with-raspberry-pi-hardware.html

Thanks,

-Prasanth

[Ismat]

Hello Prasanth

thank you very much for your comment. I am aware of the tool Simulink Support package for Raspberry Pi Hardware. But I guess it's not free.

Hence I am looking for an alternative way to write the code in Matlab/Simulink.