i tried pulling my data from arduino port but got error. I am a novice

serialPort = 'COM5';
baudrate = 115200;
s = serialport(serialPort,baudrate);

pause(4);

numsamples = 1000;

data = zeros(numsamples,4);

for i = 1:numsamples
    line = readline(s);
    values = sscanf(line, '%d,%d,%d,%d');

    if numel(values) == 3
        data(i,:) = values';
    end

    pause(0.1)
end

time = data(:,1);

figure;
plot(time, data(:,2), 'r',time, data(:,3), 'b',time, data(:,4), 'g');
xlabel('Time(s)');
ylabel('Acceleration (m/s^2)');
legend('X','Y','Z');
title('ESP_now receiver data');




Error in untitled2 (line 13)
    values = sscanf(line, '%d,%d,%d,%d');
 

[Cris LaPierre]

The error seems to suggest there is no device connected to COM5. What are the results if your run the following code?

serialportlist

[tje_b]

Thanks for your comment.I got the lines below

>> serialportlist

ans = 

  1×2 string array

    "COM4"    "COM5"

>> 

[Cris LaPierre]

Now check that it is available.

serialportlist("available")

[tje_b]

Thanks it is available, i change code and the com port to 13 in the device manger. it seems working but thie code has some errors.

% Define serial port and open the connection
serialPort = 'COM13'; % Replace with your Arduino's serial port
baudrate = 115200;
s = serialport(serialPort, baudrate);
pause(2); % Give the connection some time to be established

% Read accelerometer data from the Arduino
numSamples = 100; % Number of samples to read
data = zeros(numSamples, 3); % Preallocate a matrix to store the data

for i = 1:numSamples
    line = readline(s); % Read a line from the serial port
    values = textscan(line, '%d,%d,%d'); % Parse the line using textscan

    if numel(values) == 3
        data(i, :) = cell2mat(values)'; % Convert the cell array to a matrix and store it in the data matrix
    end

    pause(0.1); % Adjust the delay if necessary
end

% Close the serial port connection
clear s;

% Convert counts to acceleration (m/s^2)
countsPerG = 256; % For a range of +/-2g
g = 9.81; % Gravitational acceleration
data = (data / countsPerG) * g;

% Process the accelerometer data (e.g., plot it)
time = (0:numSamples - 1) * 0.1; % Assuming 100 ms delay between samples
figure;
plot(time, data(:, 1), 'r', time, data(:, 2), 'g', time, data(:, 3), 'b');
xlabel('Time (s)');
ylabel('Acceleration (m/s^2)');
legend('X', 'Y', 'Z');
title('ADXL345 Accelerometer Data');

the error is

>> untitled3
Unable to perform assignment because the size of the left side is 1-by-3 and the size of the right side is 3-by-0.

Error in untitled3 (line 18)
        data(i, :) = cell2mat(values)'; % Convert the cell array to a matrix and store it in the data matrix

[Cris LaPierre]

Sorry, I was getting distracted by the red error text appearing because you were trying to run your code here. That would be expected as hardware is not supported in the 'Run Code' feature in Answers, and is not the error you were referring to. I have removed the output from your code to remove the confusion.

Answer 1

[Walter Roberson]

    line = readline(s); % Read a line from the serial port
    values = textscan(line, '%d,%d,%d'); % Parse the line using textscan

readline(s) is returning a line that does not start with whitespace and then '-' followed by digits, or '+' followed by digits, or digits, or '-.' followed by digits, or '+.' followed by digits, or '.' followed by digits. That is, the line is either empty or is entirely whitespace or starts with something that cannot be a number.

In the case that it started with a number but then did not have a comma after the number, or had a comma followed by something that is not a number, then values{1} would contain the first number but values{2} would be empty

You should be doing something like

    line = readline(s); % Read a line from the serial port
    values = cell2mat(textscan(line, '%d,%d,%d')); % Parse the line using textscan
    if numel(values) == 3
        data(i,:) = values;
    end

The difference between this and what you are doing is that you are checking numel() on the cell array returned by textscan(), but textscan() always returns a cell array with as many elements as there are active % formats in the format description, with the cell array entries potentially being empty.

[tje_b]

Not working, maybe i am doing something wrong

Error using textscan
First input can not be empty. Expected a non-empty character vector or a valid file-id.

Error in untitled3 (line 16)
    values = cell2mat(textscan(line, '%d,%d,%d')); % Parse the line using textscan

[tje_b]

-0.33,0.55,-0.77
-0.38,0.52,-0.74
-0.38,0.58,-0.78
-0.38,0.58,-0.74
-0.36,0.60,-0.74
-0.35,0.58,-0.78

This is the output from the arduino serial monitor. I am trying to visualize and plot this in MATLAB

[Walter Roberson]

    line = readline(s); % Read a line from the serial port
    if ~isempty(strtrim(line))
        values = cell2mat(textscan(line, '%f,%f,%f')); % Parse the line using textscan
        if numel(values) == 3
            data(i,:) = values;
        end
    end

[Walter Roberson]

You should avoid using a %d format for floating point numbers.

[tje_b]

still not working , I changed to %f

[tje_b]

Error using strtrim
Input should be a string, character array, or a cell array of character arrays.

Error in untitled2 (line 13)
    if ~isempty(strtrim(line))

[Walter Roberson]

    line = readline(s); % Read a line from the serial port
    if ~isstring(line)
        error('readline returned wrong class, expected string, got %s', class(line));
    end
    line = char(line);
    
    if ~isempty(strtrim(line))
        values = cell2mat(textscan(line, '%f,%f,%f')); % Parse the line using textscan
        if numel(values) == 3
            data(i,:) = values;
        end
    end

[tje_b]

another error, thanks for your time.

readline returned wrong class, expected string, got double

[Walter Roberson]

Please show

whos s line
which serialport
which readline
which readline(s)
line

readline() is not documented as being able to return a double precision value, so we need to figure out how it is getting to be double precision.

[tje_b]

 
>> whos s line
  Name      Size            Bytes  Class                  Attributes

  line      0x0                 0  double                           
  s         1x1                 8  internal.Serialport              

>> which serialport
C:\Program Files\MATLAB\R2023a\toolbox\matlab\serialport\serialport.m
>> which readline
C:\Program Files\MATLAB\R2023a\toolbox\matlab\serialport\+internal\Serialport.m  % internal.Serialport method
>> which readline(s)
C:\Program Files\MATLAB\R2023a\toolbox\matlab\serialport\+internal\Serialport.m  % internal.Serialport method
>> line

line =

     []

[Walter Roberson]

The below version retries fetching lines, but with a maximum retry count (to guard against infinite error loop)

It turns out that for unknown reasons, readline() is returning double precision [] sometimes.

We declare a line invalid if readline() returns [] or all whitespace or otherwise does not have three floating point numbers.

% Define serial port and open the connection
serialPort = 'COM13'; % Replace with your Arduino's serial port
baudrate = 115200;
s = serialport(serialPort, baudrate);
pause(2); % Give the connection some time to be established

% Read accelerometer data from the Arduino
numSamples = 100; % Number of samples to read
data = zeros(numSamples, 3); % Preallocate a matrix to store the data

max_retries = 25;
pause_time = 0.1;   % Adjust the delay if necessary

for i = 1:numSamples

    gotline = false;
    for trycount = 1 : max_retries
        pause(pause_time);
        line = readline(s); % Read a line from the serial port
        
        %result of readline() sometimes shows up as double([])
        %but char([]) is empty char and strtrim '' is fine empty char
        %so we do not need to specifically test for []
        line = strtrim(char(line));
        if isempty(line); continue; end
        values = cell2mat(textscan(line, '%f,%f,%f')); % Parse the line using textscan
        if numel(values) == 3
            gotline = true;
            break;
        end
    end
    
    if ~gotline
        error('failed to get valid line in %d tries', max_empty_retries);
    end
    
    data(i,:) = values;
end

% Close the serial port connection
clear s;

% Convert counts to acceleration (m/s^2)
countsPerG = 256; % For a range of +/-2g
g = 9.81; % Gravitational acceleration
data = (data / countsPerG) * g;

% Process the accelerometer data (e.g., plot it)
time = (0:numSamples - 1) * 0.1; % Assuming 100 ms delay between samples
figure;
plot(time, data(:, 1), 'r', time, data(:, 2), 'g', time, data(:, 3), 'b');
xlabel('Time (s)');
ylabel('Acceleration (m/s^2)');
legend('X', 'Y', 'Z');
title('ADXL345 Accelerometer Data');

[Walter Roberson]

I suspect by the way that you might end up needing to use

configureTerminator(s,"CR")

[tje_b]

Warning: The specified amount of data was not returned within the Timeout period for 'readline'.
'serialport' unable to read any data. For more information on possible reasons, see serialport Read Warnings. 
Warning: The specified amount of data was not returned within the Timeout period for 'readline'.
'serialport' unable to read any data. For more information on possible reasons, see serialport Read Warnings. 
Operation terminated by user during matlabshared.asyncio.internal.Stream/isDeviceDone


In matlabshared.asyncio.internal.Stream/wait (line 199)
                done = obj.isDeviceDone() || ~obj.isOpen();

In matlabshared.transportlib.internal.asyncIOTransportChannel.AsyncIOTransportChannel/waitForDataAvailable

In matlabshared.transportlib.internal.asyncIOTransportChannel.AsyncIOTransportChannel/readUntil

In matlabshared.seriallib.internal.Serial/readUntil

In matlabshared.transportclients.internal.StringClient.StringClient/readRaw

In matlabshared.transportclients.internal.StringClient.StringClient/read

In internal.Serialport/readline (line 595)
                data = read(obj.StringClient, precision);

In untitled5 (line 19)
        line = readline(s); % Read a line from the serial port

[Walter Roberson]

Try adding in the configureTerminator call that I showed, right after creating the serialport object

[tje_b]

Warning: The specified amount of data was not returned within the Timeout period for 'readline'.
'serialport' unable to read any data. For more information on possible reasons, see serialport Read Warnings. 
Warning: The specified amount of data was not returned within the Timeout period for 'readline'.
'serialport' unable to read any data. For more information on possible reasons, see serialport Read Warnings. 
Unrecognized function or variable 'max_empty_retries'.

Error in untitled5 (line 36)
        error('failed to get valid line in %d tries', max_empty_retries);
        

[Walter Roberson]

% Define serial port and open the connection
serialPort = 'COM13'; % Replace with your Arduino's serial port
baudrate = 115200;
s = serialport(serialPort, baudrate);
configureTerminator(s,"CR")

pause(2); % Give the connection some time to be established

% Read accelerometer data from the Arduino
numSamples = 100; % Number of samples to read
data = zeros(numSamples, 3); % Preallocate a matrix to store the data

max_retries = 25;
pause_time = 0.1;   % Adjust the delay if necessary

for i = 1:numSamples

    gotline = false;
    for trycount = 1 : max_retries
        pause(pause_time);
        line = readline(s); % Read a line from the serial port
        
        %result of readline() sometimes shows up as double([])
        %but char([]) is empty char and strtrim '' is fine empty char
        %so we do not need to specifically test for []
        line = strtrim(char(line));
        if isempty(line); continue; end
        values = cell2mat(textscan(line, '%f,%f,%f')); % Parse the line using textscan
        if numel(values) == 3
            gotline = true;
            break;
        end
    end
    
    if ~gotline
        error('failed to get valid line in %d tries', max_retries);
    end
    
    data(i,:) = values;
end

% Close the serial port connection
clear s;

% Convert counts to acceleration (m/s^2)
countsPerG = 256; % For a range of +/-2g
g = 9.81; % Gravitational acceleration
data = (data / countsPerG) * g;

% Process the accelerometer data (e.g., plot it)
time = (0:numSamples - 1) * 0.1; % Assuming 100 ms delay between samples
figure;
plot(time, data(:, 1), 'r', time, data(:, 2), 'g', time, data(:, 3), 'b');
xlabel('Time (s)');
ylabel('Acceleration (m/s^2)');
legend('X', 'Y', 'Z');
title('ADXL345 Accelerometer Data');

If the above does not work, you will need to recheck the speed.

Are you able to use a utility such as TeraTerm to communicate with the device?

[tje_b]

No errors again, but it is not sreaming. I expected a moving signal since the data are changing but this is just static. Anyways, thank you and I really appreciate. Is there any advice on this?

[Walter Roberson]

Your code loops numSamples = 100; times, gathering data each time, and does not display anything until afterwards. It will not stream. You would need to display the data inside the loop.

% Define serial port and open the connection
serialPort = 'COM13'; % Replace with your Arduino's serial port
baudrate = 115200;
s = serialport(serialPort, baudrate);
configureTerminator(s,"CR")

pause(2); % Give the connection some time to be established

% Read accelerometer data from the Arduino
numSamples = 10000; % Number of samples to read
data = zeros(numSamples, 3); % Preallocate a matrix to store the data

countsPerG = 256; % For a range of +/-2g
g = 9.81; % Gravitational acceleration

dt = 0.1;

max_retries = 25;
pause_time = 0.1;   % Adjust the delay if necessary

hX = animatedline('Color', 'r', 'displayname', 'X');
hold on
hY = animatedLine('Color', 'g', 'displayname', 'Y');
hZ = animatedLine('Color', 'b', 'displayname', 'Z');
legend show
xlabel('Time (s)');
ylabel('Acceleration (m/s^2)');
title('ADXL345 Accelerometer Data');
hold off

for i = 0:numSamples-1

    gotline = false;
    for trycount = 1 : max_retries
        pause(pause_time);
        line = readline(s); % Read a line from the serial port
        
        %result of readline() sometimes shows up as double([])
        %but char([]) is empty char and strtrim '' is fine empty char
        %so we do not need to specifically test for []
        line = strtrim(char(line));
        if isempty(line); continue; end
        values = cell2mat(textscan(line, '%f,%f,%f')); % Parse the line using textscan
        if numel(values) == 3
            gotline = true;
            break;
        end
    end
    
    if ~gotline
        error('failed to get valid line in %d tries', max_retries);
    end
    
    data(i+1,:) = values / countsPerG * g;
    addpoints(hX, dt*i, data(i+1,1));
    addpoints(hY, dt*i, data(i+1,2));
    addpoints(hZ, dt*i, data(i+1,3));
    drawnow limitrate
end

% Close the serial port connection
clear s;

[tje_b]

SOLVED!!!

Many thanks