Real time audio data plot from COM/serial port

need to know how i can plot audio data in real-time from serial port. am getting error using this code.

clear; clc;
%create a serial object
s= serialport("COM4", 115200);
%open serial port
fopen(s);

%plotting data
i= 1;
while(1)
    data(i)= str2double(fscanf(s));
	plot(data);
	pause(0.01);
	i= i+1;
end


%error i am getting is---
Error using fopen
First input must be a file name or a file identifier.

Error in pltsril (line 5)
fopen(s);
 

Answer 1

[Cris LaPierre]

fopen does not work with a serialport object. See the available methods here:

https://www.mathworks.com/help/matlab/ref/serialport.html#mw_55ccdf03-12d9-4bd7-80c5-da8180f328d2

You likely want read.

[Walter Roberson]

Or sscanf(readline(s)) if the information is formatted as text.

Also consider using animatedline

[Kulbir]

hello sir, i am not able to plot/animate real time audio signal, would b so helpful if you share the code for that. thank you

[Walter Roberson]

@Kulbir

How are you reading the audio data?

[Kulbir]

Sir here is the code which i am being using.

device = serialport("COM3",9600)
write(device,1:5,"uint8")
read(device,5,"uint8")
while(1)% infinite loop
    i=1; %not able to see the progress line
    data(i)= str2double(fscanf(device));
	plot(data);
	pause(0.01);
	i= i+1;
	end

[Walter Roberson]

device = serialport("COM3",9600)
write(device,1:5,"uint8");
read(device,5,"uint8");

h = animatedline('MaximumNumPoints', 10000);

start = tic;
while(1)
    data = str2double(fscanf(device));
    now = toc(start);
	addpoints(h, now, data);
	drawnow limitrate
end

[Kulbir]

hi sir, the program/code is running correctly, but am not able to see plotting in the graph. As you asked how i am reading the audio data. Actually am using pressure transducer and pneumotacometer to sense vocal track aerodynamics. i have made usb operated DAC circuit. kindly help me in resolving the issue. thank you

[Cris LaPierre]

Your workspace is conspicuously empty. I would expect to see device, data, now and other variables created by your script appear there.

[Kulbir]

hi sir , i can see the device data in the workspace, when i press stop the script. but not able to see the plot in graph. plz help me out

[Cris LaPierre]

The error message is stating that you are not connected to the serial port device.

I suggest adding the following to the bottom of your script to clear your serialport object each time.

clear device

I would also suggest not using fscanf with a serialport object. Try this.

data = str2double(readline(device));

If you prefer a scan function, the use sscanf(device,"%e") instead (see here)

[Walter Roberson]

Cris beat me by a small number of seconds in pointing out you need readline().

[Kulbir]

Hi sir(s) thx for your help... unfortunately am not getting anything in the grapgh, have tried either ways. kindly help me out. as i said in my input/com device there is no microphone. its sensor/transducer and pneumotacometer as i mentioned in the trailing message. thank you

[Kulbir]

[Walter Roberson]

Did you possibly close the drawing figure?

Your code has no natural way to stop. If you tried to stop by closing the figure then you would get exactly the message you saw about needing a handle.

[Cris LaPierre]

I'll add the observation that the result of your read command appears to have been successful (variable ans in the Workspace has values), but data is NaN. Are you sure your device is streaming anything?

[Kulbir]

Hi, when i run the following script, i dont see the device data in workspace. but if i close the drawing graph, the i am able to see the data in workspace.

device = serialport("COM4",9600)
write(device,1:5,"uint8");
read(device,5,"uint8");

h = animatedline('MaximumNumPoints', 10000);

start = tic;
while(1)
data = str2double(readline(device));
now = toc(start);
	addpoints(h, now, data);
	drawnow limitrate
end

[Kulbir]

@Cris LaPierre

yes, sir, actually i am trying to capture vocal track aerodynamic signals. i have done it in c sharp. used the same animate line there. it is working in c sharp, but here i am not able to run suceesfully. my ultimate goal is to plot real time audio and vocal track pressure. thk u for helping me.

[Walter Roberson]

For testing purposes, please try this:

device = serialport("COM4",9600)

write(device,1:5,"uint8");
first_5 = read(device,5,"uint8");
fprintf('Not sure why we are reading 5 bytes, but the values received were:\n');
disp(first_5);

h = animatedline('MaximumNumPoints', 10000);

start = tic;
while isvalid(h) && toc(start) < 30               %FOR TESTING
    currentline = readline(device);
    data = str2double(currentline);
    if isnan(data)
        fprintf('data nan, line as text was: "%s"\n', currentline);
        continue;
    end
    now = toc(start);
    if isvalid(h)
	    addpoints(h, now, data);
	    drawnow limitrate
    end
end

At this point I would not be surprised if it turned out that each line of data received is text with multiple numeric values.

[Kulbir]

Sir, this is what i am geeting from the device in Tera Term tool

[Cris LaPierre]

It would be more helpful to see the results in MATLAB

[Kulbir]

@Walter Robers

Hi sir, thank you, now i am getting the output in the command windows.

[Kulbir]

@Cris LaPierre

yes sir, can see it in the matlab, plz check the trailing communication. thank you

[Kulbir]

hi sir(s), i would like to say, there is a knob/button on my device to collect the data, but i am geeting this data without pressing the button

[Walter Roberson]

So far, except for the first 5 bytes, your code has been as-if the data being sent from the other side is text. For example your existing code is expecting to receive lines similar to

0.15180

-0.3351

as text .

But the other end is not sending text, it is sending binary values. Instead of using readline() and str2double(), you need to use read . But to use that successfully, you need to know what format the other end is sending the samples. The most common data formats would correspond to

read(device, 1, 'uint8')    %8 bit unsigned data
read(device, 1, 'uint16')   %16 bit unsigned data, little-endian
read(device, 1, 'float')    %32 bit single precision, little-endian
swapbytes(read(device, 1, 'uint16'))   %16 bit unsigned data, big-endian
swapbytes(read(device, 1, 'float'))    %32 bit single precision, big-endian

but there are other possibilities as well.

For example, it would not be uncommon to send packed 12-bit data, 2 samples stored across 3 bytes.

[Kulbir]

@Walter Roberson

sir tried with the new script, getting the data in different way, less coulmns. thank you for helping me.

[Kulbir]

sir there are two channels in my device. but i think that is not the part of our discussion. i am expecting plotting of audio signal firsty. thank you

[Walter Roberson]

Using readline(device) is not going to be useful for you. You need to find out what data format the device is sending, and you need to use read() of the device, probably using one of the commands I showed above.

What model of device are you reading from?

[Kulbir]

@Cris LaPierre@Walter Roberson

hello sir, i am in need your inputs, thank you