Keep the latest desired value before changing to undesired value

Hello,

So let state that the signal X has four states [0,1,2,3]. The values 2,3 are not "good" values and you want to keep the value of the signal among the good ones as soon as the signal gets the bad value. Let me explain more:

at t = 0 X = 0 so nothing needs to happen

at t = 1 X = 1 so nothing needs to happen

at t = 2 X = 2 . This is the undesired value. we take the last desired value which was X=1

at t = 3 X = 3. This is undesired value. we take the last desired value which was X=1

at t = 4 X = 0. This is desired value. so X is now 0.

at t = 5 X = 1. This is desired value so X is now 1

So what I am trying to do is to save the last desired know value and I am trying to make it happen in Simulink. Not sure how to do this.

Answer 1

[Peppe]

So what I did was the following:

[Les Beckham]

That looks like it should work. I was thinking about something like that. But, since I don't have Simulink to test with, I provided a different approach that I was able to test.

Answer 2

[Les Beckham]

There might be a way to do this using just basic Simulink blocks, but I don't have Simulink right now to test with. So, I'm going to suggest using a Matlab Function block with the following code in it:

function [out] = rejectUndesiredValues(in)

persistent lastout

undesiredValues = [2 3];

if ~exist('lastout', 'var')

lastout = 0; % default to outputting zero if an undesired value is the first input

end

if ~ismember(in, undesiredValues)

out = in; % update the output if the input is not an undesired value

else

out = lastout; % otherwise, repeat the last desired value

end

lastout = out; % update the past value of the output

end

% Let's test it
format compact
x = [0 1 2 3 0 1 0 3 2];
y = zeros(size(x));
for idx = 1:numel(x)
    y(idx) = rejectUndesiredValues(x(idx));
end
disp(x)

     0     1     2     3     0     1     0     3     2

disp(y)

     0     1     1     1     0     1     0     0     0

function [out] = rejectUndesiredValues(in)
persistent lastout
undesiredValues = [2 3];

if ~exist('lastout', 'var')
    lastout = 0; % default to outputting zero if an undesired value is the first input
end

if ~ismember(in, undesiredValues)
    out = in; % update the output if the input is not an undesired value
else
    out = lastout; % otherwise, repeat the last desired value
end
lastout = out; % update the past value of the output

end

[Peppe]

Thank. I made a solution as well. But please let me know if that is efficient.