How can I display on a Simulink Scope a digital signal that I am receiving in packages of N samples from a device via serial communication (i.e. [Nx1] array)

I am working on a simulink model that receives data from a device via serial communication and performs data processing and visualization.

The device sends the data of a signal in packages of N samples, i.e. every time a read from the serial port and I parse the serial message from the device, I end up with a Nx1 array, where each element of the array is one sample of the signal. How do I display this signal in time using a Scope block (or something equivalent)? If I just connect the Nx1 array to a Scope block, the scope shows N signals.

[Beda Alessandro]

Update: if you have the DSP Toolbox installed, the solution is go to the Configuration Properties of the Scope block and change the "Input Processing" option from "Elements as channels (sample based)" to "Columns as channels (frame based)". Note that you need to feed a colum vector (i.e., [1xN]) to the Sope block, so you might need to use a "Transpose" block.

Answer 1

[Pratyush Swain]

Hi Beda,

I understand when you connect an Nx1 array directly to a Scope block, it interprets each element of the array as a separate signal , hence showing N signals. One workaround is we can leverage "MATLAB function block" to process the data such that it is treated as a sequence of samples from a single signal rather than as multiple signals.

I simulated the Nx1 input by using "repeating sequence block","constant block", and "vector concatenation block".

The "MATLAB function Block" has the following implementation to extract the vector data sequentially:

% y is the single output, u is the vector input %
function y = fcn(u)
    % Declaring persistent variables buffer and index
    persistent buffer index
    
    % If the buffer is empty, initialize it with zeros
    if isempty(buffer)
        buffer = zeros(size(u));
        index = 1;
    end
    
    % Allocate input vector values to buffer and extract value at index
    buffer = u;
    y = buffer(index);
    
    % Update index
    index = index + 1;
    
    % If index exceeds array bounds, initialize it to 1 
    if index > length(buffer)
        index = 1;
    end
end

The above function block will ensure the values of the vector are outputted sequentially.The following is the output when three different signals[3X1] are realized in simulink scope(output of vector concatenation block):

After the application of "MATLAB function block" we get a single continous signal as compared to three different signals as follows:

We can also visualize how the above signal is infact made from the values of the three input signal as follows:

For more information on "MATLAB function block" and "vector concatenation block" please refer to:

1. https://www.mathworks.com/help/simulink/slref/matlabfunction.html

2. https://www.mathworks.com/help/simulink/slref/vectorconcatenate.html

I have also attached the simulink model for your reference.

Hope this helps.

[Beda Alessandro]

Dear Adit,

thanks for taking the time to answer, but the answer is not correct. Your matlab function is outputting 1 sample for each simulation step , which means that you are loosing the values of the other samples for that step, for the simple reason that at each step you are producing 4 samples of data. If you look at the figures your scopes, if everything was correct, than the values of sample 1,2,3,4 etc in the red signal in "Scope" (first figure), must correspond the values of the samples 3,6,9,12 in the "Scope1" (second figre), respectively. This is not the case.

Ale

[Pratyush Swain]

Hi Beda,

Thanks for the observation,as rightly pointed out, the MATLAB function block loses values. For the purpose of solely realizing the values in [Nx1] array, we can use the "array plot" block in simulink .

In the example model above,the values from "constant" block which is of dimension [1X10] are realized in the array plot block as follows:

Please note,If your values are in form of column vector [Nx1], you might want to consider using a "reshape" block to convert it into 1-D vector.

If this still does not satisfy your usecase, you can try saving the values to workspace using the "To workspace" block in simulink and then plot the values later.

Hope this helps in resolving your issue.

[Beda Alessandro]

Hi Swain, the only issue I have with "vector plot" block is that it requires DSP toolbox and signal processing toolboxes, which I do not have the licenses for ;-). But, if you have these two licenses, then you can solve the problem directly in the Scope block, by changing in the Configuration Properties of the block the Input Precessing from "Elements as channels (sample based)" to "Columns as channels (frame based)". Then you just need to make sure that your input is a column vector (as you mentioned for the array plot block), and you are good to go.

[Pratyush Swain]

Hi Beda,

I guess we can conclude the "array plot" block satisfies the requirement but the only issue is the license. Also the "scope" block workaround which you mentioned is nice to know,thanks.

[Beda Alessandro]

Not really, the ''vector plot" alllows you to visualize only the samples of the signal that are available at each simulation step, not the evolution of the signal in time. To have that result, the only option is to use the scope with the configuration of Input processing as "Columns as channels (frame based)"

[Pratyush Swain]

Hi Beda,Do you specifically require licenses to set the configuration settings of scope block ?

[Beda Alessandro]

only for changing "Input Processing" configuration settings, not for the other settings