problem with code for arduino voltage reading

Doing a project with pulse sensor on arduino followed a code online it hit an error im unable to understand im still learning matlab at a basic level can anyone help this is the coding error

Undefined function 'readVoltage' for input arguments of type 'matlab.graphics.axis.Axes'.

Error in mypulsesensor (line 85)

data(i) = readVoltage(a,'A0'); % read voltage on pin A0, store as next data point

[Geoff Hayes]

Muhammad - what is variable a in your

data(i) = readVoltage(a,'A0')

? The error message is suggesting that this may be an axes and not the arduino (which you are trying to read from). You may need to post more of your code so that we can see how you have defined variables for the axes and arduino.

[Muhammad Alief Nasarudin]

a for the arduino connection ill give the full code here.this is base on a code i found

 clear a
 a=arduino();
 

% choice = 1 tells the program to collect data; (automatically calculates heart rate) 
% choice = 2 closes all figures
choice = 1; 

points = 150;   % specify the number of times to measure the output voltage
                % Since data is acquired approximately every 0.03 sec, 350
                % data points should be about 10 seconds of pulse data
                %for some reason 350 points of data is too much
                %150 plots a little over 10 seconds of pulse data

% choose the upper and lower bounds of the y axis, the lowest and highest
% Vout values you expect to see. **CHANGE THESE VALUES HERE IF DESIRED.**
lowestvoltage = 1.8;    
highestvoltage = 4.5;

% set up a row vector "data" to collect the voltage due to the reflected light 
% receieved by the photodiode. Set up row vector "time" to store the time 
% index of each data point
format shortg;
timestart = clock;                  %format to user timers (attempt to change time axis)

begxaxis = 0;
endxaxis = 10;

while (choice == 1) % while user wants to collect new waveforms, poll pulse sensor and plot output
    
    data = zeros(1, points);     % initialize vector to hold sensor voltagae data
    time = zeros(1, points);    % initialize vector to hold time index of each voltage
    
    figure;              % create a new figure window for plotting the Vout values
    axis([begxaxis endxaxis lowestvoltage highestvoltage]);  % set the lower and upper limits of the x and y values
    xlabel('time, seconds');
    ylabel('Output voltage, volts');
    hold on             % freeze the graph so that you can plot each new Vout value on the same graph
    grid on
    grid minor
    
    tstart = tic;       % start a timer
    data(1) = readVoltage(a,'A0'); %read the voltage on pin A0 and store as the first data point
    time(1)= toc(tstart);       %store the time index of that data point in "time"
    
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % The following lines of code read the A0 voltage and note the time
    % index. These values are stored in "data" and "time", respectively
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    minVoltage = data(1);
    maxVoltage = data(1);
    
    beattime = zeros(1,15);
    beatcount = 1;
    intervals = zeros(1,14);
    
    %{
    timenow = clock;
    if (etime(timenow,timestart) >= 2)
        fprintf('This worked');
        begxaxis = begxaxis + 1;
        endxaxis = endxaxis + 1;
        %will this work: 
        figure;
        
        axis([begxaxis endxaxis lowestvoltage highestvoltage]);  
        timestart = timenow;
    end
    %}
  
        
    
    for i=2:points
        data(i) = readVoltage(a,'A0'); % read voltage on pin A0, store as next data point
        
        if (data(i) > maxVoltage)
            maxVoltage = data(i);
        elseif (data(i) < minVoltage)
            minVoltage = data(i);
        end
            
        time(i) = toc(tstart);      % store corresponding time index
        
        %formatting for scrollable plot
        dx = 2;
        a = gca;
        
        
        
        plot(time(i-1:i), data(i-1:i));  %draw the line from the last Vout value to the current Vout value
        
        %actual scroller
        %Set appropriate axis limits and settings
        set(gcf, 'doublebuffer', 'on');
        %Avoiding flickering when updating
        set(a,'xlim',[0 dx]);
        set(a,'ylim',[min(50) - 1, max(200) + 1]); %REMEMBER TO CHANGE X AND Y
        
        %Generate constants for use in UI Control intialization
        pos = get(a, 'position');
        Newpos = [pos(1) pos(2)-0.1 pos(3) 0.05];
        %Slider and leader room for axis labels
        xmax = max(100);
        S = ['set(gca,''xlim'',get(cbo,''value'')+[0 ' num2str(dx) '])'];
        
        %UI Control
        h = uicontrol('style','slider',...
            'units', 'normalized', 'position', Newpos,...
            'callback',S,'min',0,'max',xmax-dx);
        
        drawnow;
        
        thresh = maxVoltage * 0.95;
        if (data(i) > thresh) && (time(i) > beattime(beatcount)+0.4)
            beatcount = beatcount + 1;
            beattime(beatcount) = time(i);
        end
         
        for i=1:beatcount-1
            intervals(i)= beattime(i+1)-beattime(i);
        end
        
        avgbeat=median(intervals);
        bpm=60/avgbeat; % Calculate average heart rate in beats per minute
        title(['Heart Rate = ', num2str(bpm, 4), ' beats per minute (using threshold = ', num2str(thresh,3),' volts)']);
        
    end

    choice = menu('Would you like to keep collecting data?', 'Collect a new set of pulse waveforms','Close');
end

%{
while (choice == 2)                    (Changing axis would be too slow
                                                Replot too much data
    
    finish=false;
    set(gcf,'CurrentCharacter','@'); % set to a dummy character
    while ~finish
    % do things in loop...
    
    % check for keys
    k=get(gcf,'CurrentCharacter');
     if k~='@' % has it changed from the dummy character?
       set(gcf,'CurrentCharacter','@'); % reset the character
       % now process the key as required
      if k=='q', finish=true; end
     end
end
    
  
if choice == 2,
    close all;
end

%}

Answer 1

[Geoff Hayes]

Muhammad - the problem is with this line of code

a = gca;

where you overwrite the arduino assigned variable with the current axes...and so when you reference a again with

data(1) = readVoltage(a,'A0'); 

the error occurs because now a is the axes. Consider an alternative name for the axes variable (one that perhaps describes what it references)

hCurrentAxes = gca;     
plot(time(i-1:i), data(i-1:i));  %draw the line from the last Vout value to the current Vout value

%actual scroller
%Set appropriate axis limits and settings
set(gcf, 'doublebuffer', 'on');
%Avoiding flickering when updating
set(hCurrentAxes,'xlim',[0 dx]);
set(hCurrentAxes,'ylim',[min(50) - 1, max(200) + 1]); %REMEMBER TO CHANGE X AND Y

%Generate constants for use in UI Control intialization
pos = get(hCurrentAxes, 'position');

or just use gca instead.

You could also rename the variable for the arduino "handle" to something that is more descriptive.

[Muhammad Alief Nasarudin]

thank you i was able to make it work and the reading was ok