Getting Started With Analog Input (Data Acquisition Toolbox)

Data Acquisition Toolbox

Creating an Analog Input Object

Before executing an analog input (AI) task, an analog input object must be created. You create an AI object with the command

AI = analoginput('adaptor', ID);

where:

analoginput is the analog input object creation function
adaptor is the hardware driver adaptor name
ID is the vendor-specific device label
AI is the analog input object

The valid device object creation function arguments are given below.

Table 3-1: **Analog Input Object Creation Function Argument Values**
Value	Description	Supported Drivers
Value	Description	Sound Cards	NI	HP VXI
`adaptor`	Adaptor name	`winsound`	`nidaq`	`hpvxi`
`ID`	Device label	N/A	Device number	Device id

If the hardware driver adaptor has been successfully registered by the data acquisition engine, then an analog input object can be created. Once the device object is created, then:

If this is the first device object to reference a particular driver, that driver is loaded into memory and initialized.
The device object is linked to the specified hardware device through the hardware driver.
A unique analog input object name is automatically created and assigned to the Name property. The name is created by concatenating the name of the adaptor, the device label, and the device object type. You can change the value of Name at any time. For sound cards, only the name of the adaptor and the device object type is used.

By default, no hardware channels are associated with a newly created analog input object. To associate channels with the device object, the addchannel function must be used.

Example: Create an Analog Input Object

Suppose you want to create the analog input object AI for a sound card. Since there is no device label for the sound card, the analog input object creation function requires only the adaptor name as an argument.

AI = analoginput('winsound');

An analog input object called AI now exists in the MATLAB workspace and the engine. The device object's name can now be displayed.

get(AI,'Name')
ans =
winsound0-AI

If you are familiar with Handle Graphics®, then AI may look like a handle to you. In fact, it is not a handle but a Data Acquisition Toolbox object. To verify this, type whos AI at the command line.

whos AI
  Name      Size         Bytes  Class
  AI        1x1           1332  analoginput object
Grand total is 52 elements using 1332 bytes

AI cannot yet be used to acquire data since it has no hardware channels associated with it. Additionally, property values must be set to establish the required behavior for your specific application.

[ Previous | Help Desk | Next ]