Acquire Data in Background with Live Plot Updates

This example shows how to acquire data in the background using callbacks while MATLAB^® continues to run.

A background acquisition uses callbacks to access data as the hardware collects it or to handle errors as they occur. In this example, you acquire data from a microphone with ID Audio1, and you define a callback for the ScansAvailableFcn property to update a plot in real time while acquisition continues.

A background acquisition uses callbacks to allow your code to access data as the hardware acquires it or to react to any errors as they occur. In this example, you acquire data from a microphone with ID Audio1 using the ScansAvailableFcnCount property to trigger the function call defined by the ScansAvailableFcn property. Using a callback allows a plot to be updated in real time while acquisition continues.

Device Discovery and Setup

Get a list of devices so you can identify the microphone you want to use. The partial listing here indicates the device ID.

daqlist

      VendorID       DeviceID                         Description
    _____________    ________    ____________________________________________________

    "directsound"    "Audio1"    "DirectSound Headset Microphone (Plantronics BT600)"

Create a directsound DataAcquisition object with a microphone input channel on Audio1.

d = daq("directsound");
ch = addinput(d,"Audio1",1,"audio");

Background Acquisition and Live Plot Setup

Configure a callback function using the ScansAvailableFcn property to update a live plot with the data from background acquisition. This callback is triggered when the number of scans accumulated exceeds the default value of ScansAvailableFcnCount property.

d.ScansAvailableFcn = @plotMyData;

Start the acquisition to run for 5 seconds in the background.

start(d,"Duration",seconds(5))

Create a live-updating line plot by storing its handle in the UserData property of the data acquisition object. This allows the callback function to access and update the line plot dynamically during the background acquisition process.

figure;
xlabel("Time (s)");
ylabel("Amplitude");
d.UserData = animatedline;

Callback Function

This callback function updates the live plot with the data acquired in the background.

function plotMyData(src,evt)
% src is the DataAcquisition object passed in. and evt is not used.
     [data, timestamps, ~] = read(src, src.ScansAvailableFcnCount, 'OutputFormat', 'Matrix');
      addpoints(src.UserData, timestamps , data);
 end

During the background acquisition, speak into the microphone and see the plot update in real time.