Transition Your Code from Session to DataAcquisition Interface

This topic helps you transition your code from the session interface to the DataAcquisition interface.

Transition Common Workflow Commands

This table lists the session interface commands for common workflows and their corresponding DataAcquisition interface commands.

To do this	Session Command	DataAcquisition Command
Find supported hardware available to your system	daq.getDevices	daqlist
Reset toolbox to initial state	daqreset	daqreset
Create interface object	s = daq.createSession('ni')	d = daq("ni");
Add analog input channel	addAnalogInputChannel(s,'Dev1',1,'Voltage')	addinput(d,"Dev1","ai1","Voltage")
Add analog output channel	addAnalogOutputChannel(s,'Dev1',0,'Current')	addoutput(d,"Dev1","ao1","Current")
Add digital input line	addDigitalChannel... (s,'Dev1','Port0/Line0:1','InputOnly')	addinput(d,"Dev1","port0/line1","Digital");
Add counter input channel	addCounterInputChannel... (s,'Dev1','ctr0','EdgeCount')	addinput(d,"Dev1","ctr0","EdgeCount");
Queue data for output	queueOutputData(s,outputSignal);	preload(d,outputSignal); (Necessary only for background operation.)
Start operation	startForeground(s); startBackground(s);	For foreground operations that block MATLAB® when running: write(d,signalData) read(d,8000) readwrite(d,8000) For background operations that run without blocking MATLAB: preload(d,outputSignal); start(d)
Set data scan rate	s.rate = 48000	d.Rate = 48000;
Specify external trigger	addTriggerConnection... (s,'External','Dev3/PFI0','StartTrigger');	addtrigger(d,"Digital","StartTrigger","External","Dev3/PFI0");
Specify input signal range	ch = addAnalogInputChannel... (s,'Dev1',1,'Voltage'); ch.Range = [-5 5];	ch = addinput(d,"Dev1","ai4","Voltage"); ch.Range = [-5 5];

Acquire Analog Data

Session Interface

Using the session interface, you create a vendor session and add channels to the session. You can use any device or chassis from the same vendor available to your system and can add a combination of analog, digital, and counter input and output channels. All the channels operate together when you start the session.

1. Find hardware available to your system.

   d = daq.getDevices

2. Create a session for National Instruments™ devices.

   s = daq.createSession('ni');

3. Set the session scan rate to 8000.

   s.Rate = 8000

4. Add an analog input channel for the device with ID Dev1 for voltage measurement, and then start the acquisition.

   addAnalogInputChannel(s,'Dev1',1,'Voltage');
   startForeground(s);

DataAcquisition Interface

1. Find hardware available to your system.

   devs = daqlist

2. Create a DataAcquisition for National Instruments devices.

   d = daq("ni");

3. Set the DataAcquisition scan rate to 8000.

   d.Rate = 8000

4. Add an analog input channel for the device with ID Dev1 for voltage measurement, and then start the acquisition.

   addinput(d,"Dev1","ai1","Voltage");
   data = read(d,4000);

   Scan results are returned to the timetable data.

Use Triggers

Acquire analog data using hardware triggers.

Session Interface

You can specify an external event to trigger data acquisition using the session interface.

1. Create a session and add two analog input channels.

   s = daq.createSession('ni');
   ch = addAnalogInputChannel(s,'Dev1',0:1,'Voltage');

2. Configure the terminal and range of the channels in the session.

   ch(1).TerminalConfig = 'SingleEnded';
   ch(1).Range = [-10.0 10.0];
   ch(2).TerminalConfig = 'SingleEnded';
   ch(2).Range = [-10.0 10.0];

3. Create an external trigger connection and set the trigger to run one time.

   addTriggerConnection(s,'External','Dev1/PFI0','StartTrigger');
   s.Connections(1).TriggerCondition = 'RisingEdge';
   s.TriggersPerRun = 1;

4. Set the rate and the duration of the acquisition.

   s.Rate = 50000;
   s.DurationInSeconds = 0.01;

5. Acquire data in the foreground and plot the data.

   [data,timestamps] = startForeground(s);
   plot(timestamps,data)

DataAcquisition Interface

1. Create a DataAcquisition and add two analog input channels.

   d = daq("ni");
   ch = addinput(d,"Dev1",0:1,"Voltage");

2. Configure the terminal configuration and range of the channels in the DataAcquisition.

   ch(1).TerminalConfig = "SingleEnded";
   ch(1).Range = [-10.0 10.0];
   ch(2).TerminalConfig = "SingleEnded";
   ch(2).Range = [-10.0 10.0];

3. Create an external trigger connection and set the trigger to run one time.

   addtrigger(d,"Digital","StartTrigger","Dev1/PFI0","External");
   d.DigitalTriggers(1).Condition = "RisingEdge";
   d.NumDigitalTriggersPerRun = 1;

4. Set the scan rate of the acquisition.

   d.Rate = 50000;

5. Acquire data in the foreground for 0.01 seconds and plot the data from all channels.

   data = read(d,seconds(0.01));
   plot(data.Time, data.Variables)

Initiate an Operation When Number of Scans Exceeds Specified Value

You can specify your acquisition to watch for a specified number of scans to occur and then initiate some operation.

Session Interface

The session interface uses listeners and events to trigger certain actions. The NotifyWhenDataAvailableExceeds property can fire a DataAvailable event. A listener defines the operation to execute at that time.

1. Create an acquisition session, add an analog input channel.

   s = daq.createSession('ni');
   addAnalogInputChannel(s,'Dev1','ai0','Voltage');

2. Set the scan rate to 800,000 scans per second, which automatically sets the DataAvailable notification to automatically fire 10 times per second.

   s.Rate = 800000;
   s.NotifyWhenDataAvailableExceeds

   ans =
       80000

3. Increase NotifyWhenDataAvailableExceeds to 160,000.

   s.NotifyWhenDataAvailableExceeds = 160000;

4. Add a listener to determine the function to call when the event occurs.

   L = addlistener(s,'DataAvailable', ...
          @(src,event)readAndLogData(src));

DataAcquisition Interface

The DataAcquisition interface uses callback functions that execute at occurrences determined by certain properties. The ScansAvailableFcnCount property determines when to initiate the callback function defined by ScansAvailableFcn.

1. Create a DataAcquisition interface and add an analog input channel.

   d = daq("ni");
   ch = addinput(d,"Dev1",1,"Voltage");

2. Set the scan rate to 800,000 scans per second, which automatically adjusts the ScansAvailableFcnCount property.

   d.Rate = 800000;
   d.ScansAvailableFcnCount

       80000

3. Increase ScansAvailableFcnCount to 160,000.

   d.ScansAvailableFcnCount = 160000;

4. Identify a callback function for when the count occurs.

   d.ScansAvailableFcn = @readAndLogData;

Analog Output Generator Code

To compare session interface code and DataAcquisition interface code you can use the code generated by the Analog Output Generator in MATLAB releases R2019b and R2020a. In both these examples, the generator created a 10 Hz test signal sine wave for 1 second on a single channel of a National Instruments USB-6211.

%% Auto-generated by Data Acquisition Toolbox Analog Output Generator in MATLAB R2020a.
%% Create DataAcquisition Object
% Create a DataAcquisition object for the specified vendor.

d = daq("ni");
%% Add Channels
% Add channels and set channel properties, if any.

addoutput(d,"Dev1","ao0","Voltage");
%% Set DataAcquisition Rate
% Set scan rate.

d.Rate = 250000;
%% Define Test Signal
% Create a test sine wave signal of specified peak-to-peak amplitude for each 
% channel.

amplitudePeakToPeak_ch1 = 20;

sineFrequency = 10; % 10 Hz
totalDuration = 1; % 1 seconds

outputSignal = [];
outputSignal(:,1) = createSine(amplitudePeakToPeak_ch1/2, ...
                        sineFrequency, d.Rate, "bipolar", totalDuration);
outputSignal(end+1,:) = 0;
%% Generate Signal
% Write the signal data.

write(d,outputSignal);
%% Clean Up
% Clear all DataAcquisition and channel objects.

clear d outputSignal
%% Create Test Signal
% Helper function for creating test sine wave signal.

function sine = createSine(A, f, sampleRate, type, duration)

numSamplesPerCycle = floor(sampleRate/f);
T = 1/f;
timestep = T/numSamplesPerCycle;
t = (0 : timestep : T-timestep)';

if type == "bipolar"
    y = A*sin(2*pi*f*t);
elseif type == "unipolar"
    y = A*sin(2*pi*f*t) + A;
end

numCycles = round(f*duration);
sine = repmat(y,numCycles,1);
end

%% Auto-generated by Data Acquisition Toolbox Analog Output Generator in MATLAB R2019b
%% Create Data Acquisition Session
% Create a session for the specified vendor.

s = daq.createSession('ni');
%% Set Session Properties
% Set properties that are not using default values.

s.Rate = 250000;
%% Add Channels to Session
% Add channels and set channel properties.

addAnalogOutputChannel(s,'Dev1','ao0','Voltage');
%% Define Test Signal
% Create a test sine wave signal of specified peak-to-peak amplitude for each 
% channel.

amplitudePeakToPeak_ch1 = 20;

sineFrequency = 10; % 10 Hz
totalDuration = 1; % 1 seconds

outputSignal(:,1) = createSine(amplitudePeakToPeak_ch1/2, ...
                        sineFrequency, s.Rate, 'bipolar', totalDuration);
outputSignal(end+1,:) = 0;
%% Queue Signal Data
% Make signal data available to session for generation.

queueOutputData(s,outputSignal);
%% Generate Signal
% Start foreground generation

startForeground(s);
%% Clean Up
% Clear the session and channels.

clear s outputSignal
%% Create Test Signal
% Helper function for creating test sine wave signal.

function sine = createSine(amplitude, frequency, sampleRate, type, duration)

sampleRatePerCycle = floor(sampleRate/frequency);
period = 1/frequency;
s = period/sampleRatePerCycle;
t = (0 : s : period-s)';

if strcmpi(type, 'bipolar')
    y = amplitude*sin(2*pi*frequency*t);
elseif strcmpi(type, 'unipolar')
    y = amplitude*sin(2*pi*frequency*t) + amplitude;
end

numCycles = round(frequency*duration);
sine = repmat(y, numCycles, 1);
end

Previous Interface Help

The DataAcquisition interface is supported in R2020a and later. If you are using an earlier release, use the session interface instead. For more information and examples of the session interface, see Data Acquisition Toolbox Documentation (R2019b).