MATLAB: How to synchronize acquired digital and analog signals at different rates using Data Acquisition Toolbox

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I would like to read in both the digital and analog inputs from my I/O board using Data Acquisition Toolbox, but they are acquired at a different rate.

Best Answer

You can acquire the digital signal on an analog channel by connecting the physical wire which is the digital input to an analog input channel. Then you can read the digital input as an analog input and get a series of data points corresponding to the digital signal over time, using the following command:

      [data, time] = getdata(ai);

The digital data will be in the column that corresponds to that channel and it will be synchronized with the columns that represent the analog input.

The Data Acquisition Toolbox documentation includes an example on "Counting Complex Events Using Analog Input Data" which should be helpful.

Digital IO objects in the DAQ toolbox are fundamentally different from Analog IO objects. With digital IO objects you only read and write single values. Consult the documentation for further information on this difference.

You can't really "record" data from a digital IO object. Options include connecting the digital IO signal to an analog channel as described above, or creating a loop in MATLAB to continuously read the digital signal or using timer callbacks to record values at specific intervals.

Related Solutions

MATLAB: How to read from multiple modules on a compactDAQ using the DAQ Toolboox

There are two interfaces for data acquisition. The older Session interface and the new DataAcquisition interface. In either case, you just add input channels to your session/daq object for each input and module.

For example, with the Session interface:

s = daq.createSession('ni');
addAnalogInputChannel(s, 'cDAQ1Mod1', 'ai0', 'Voltage');
ch = addCounterInputChannel(s, 'cDAQ1Mod2', 'ctr0', 'EdgeCount');
% ... add more input channels as needed

ch.Terminal % examine the terminal and wire to it accordingly

s.Rate = 10;
s.DurationInSeconds = 1;
data = startForeground(s);

While for the DataAcquisition interface:

dq = daq("ni");
addinput(dq, "cDAQ1Mod1", "ai0", "Voltage");
ch = addinput(d,"cDAQ1Mod5","ctr0","EdgeCount"); 
% ... add more input channels as needed
ch.Terminal % examine the terminal and wire to it accordingly
dq.Rate = 1000;
data = read(dq, seconds(5));

For a comparison, between the interfaces, see:https://www.mathworks.com/help/releases/R2020b/daq/transition-your-code-from-session-to-dataacquisition-interface.html

MATLAB: How to synchronize analog intputs and outputs using Data Acquisition Toolbox

Synchronization of analog inputs and outputs can only be achieved through the use of hardware triggering. It is also possible to trigger two analog input objects at approximately the same time using software triggering, however they will not be synchronized.

If you wish to use hardware triggering, you will need to make sure that your hardware is capable of the type of synchronization you want to do. For example, some boards may have separate trigger pins for analog inputs and outputs. Please see the following page for a list of the hardware supported by Data Acquisition Toolbox:

https://mathworks.com/hardware-support/data-acquistion-software.html

The following example shows how to use analog input channels and analog output channels together with a single Session object running near simultaneous.

https://www.mathworks.com/help/daq/examples/acquire-data-and-generate-signals-at-the-same-time.html

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Related Solutions

MATLAB: How to read from multiple modules on a compactDAQ using the DAQ Toolboox

MATLAB: How to synchronize analog intputs and outputs using Data Acquisition Toolbox

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