Language - MATLAB

Support

If this is your first time working with a Phidget, we suggest starting with the Getting Started page for your specific device. This can be found in the user guide for your device. That page will walk you through installing drivers and libraries for your operating system, and will then bring you back here to use MATLAB specifically.

MATLAB is capable of using the non-event driven part of the Phidget API. We also provide example code in MATLAB for AdvancedServo, Encoder, InterfaceKit, Servo and Stepper.

MATLAB can be developed with any operating system that can run MATLAB code.{{{5}}}

You can compare MATLAB with our other supported languages.

If you want to use the events provided by the Phidget library (for, say, collecting sensor data as it changes) then consider using Python as a wrapper. Python has many libraries which can provide MATLAB-like functionality, such as:

• MatplotLib (plotting functions very similar to MATLAB)
• NumPy (array functions similar to MATLAB)
• SciPy (scientific functions similar to MATLAB libraries)

There is also Pytave, which interfaces with Octave, which can read .m files. Using the list of libraries above would mimic MATLAB abilities in Python. Using Pytave would allow you to open most MATLAB code directly, as long as it works on Octave. In both of these cases, you would use the Python Phidget libraries, and Python as your main Phidget programming language, not the MATLAB. Python has excellent [web documentation], and it is interpreted like MATLAB so there is no need to compile.

Quick Downloads

Just need the MATLAB drivers, libraries, and examples? Here they are.

• MATLAB Sample Code, including the phidget21Matlab.h library file, needed for any MATLAB project.

MATLAB depends on the C/C++ libraries, and all MATLAB calls essentially call functions in the C library. So. you need the C/C++ drivers and libraries, and you may also find the C/C++ API reference handy:

• C/C++ API Manual Download or (HTML online version)
• General API (more help on functions common to all Phidgets)
• Device Specific APIs (more help on functions specific to your Phidget)

Libraries and Drivers which MATLAB depends on:

• 32 bit Windows (drivers, with libraries)
• 64 bit Windows (drivers, with libraries)
• General Linux Libraries ( Linux Library Setup Instructions)
• General Mac OSX Libraries ( Mac OSX Library Setup Instructions)

Getting Started

Run The Examples

One good way to start developing your application is to run and modify existing examples. You can find the MATLAB example code here:

• MATLAB Examples
• C/C++ API, the basis for MATLAB calls

Copy phidget21Matlab.h from the examples folder to your project directory where you will also put the .m file you want to run.

To run the example code, you'll need to find the source code for your specific device within the example package. If your device does not have an example written for it, try the HelloWorld.m example. Then, run the code within MATLAB as you would any .m file. This will allow you to:

• Make sure your libraries are properly linked
• Go from source code to a test application as quickly as possible
• Ensure your Phidget is hooked up properly

Follow The Examples

The examples for each device all have this general structure so you can follow along. We also have an in-depth general introduction to writing Phidget code (like open, read data, etc), as well as the {{{2}}} for specific syntax:

// ----- Main Code ----- Create Device Software Object Open Device Wait until Device Attachment Initialize any hardware (antennas, etc) Loop waiting on requests from user input Get and Print various device statuses on request by input Exit upon specific user input Close Device Delete Device

Because the user must ask for everything in MATLAB (rather than using events to detect when things occur) there is only one main code loop. All of the Phidget functions used are simply calls, through MATLAB, to the C library. You can find the syntax for how each of these are used in the examples within the Write Your Own Code section below.

Write Your Own Code

General Library Setup

Before you can use the Phidget, you must include a reference to the library in the code in the main body of code. Copy phidget21Matlab.h to your project directory and then in MATLAB:

  function phidgettest(n)
     loadlibrary phidget21 phidget21Matlab.h;
      % More code goes here
  end

Create and Build Your Project

Programming with Phidgets makes extensive use of the calllib() function to the C/C++ library, so the C/C++ API reference will be helpful:

• C/C++ API (This is the complete set of functions you have available for all Phidgets)
• Device Specific APIs - The one for your Phidget can be found in its user guide.

To learn the details behind opening, configuring, using, and closing your Phidget, try the General Phidget Programming page. That page also describes using the Phidget in an event-driven manner and in a traditional manner, although you can only use the logic code type design in MATLAB.

Specific calls in MATLAB will differ in syntax from those on the General Phidget Programming page, but the concepts stay the same. For example, if we were using a Phidget Interface Kit as our device, the general calls would look like this:

Step One: Initialize and Open

  devicePointer = libpointer('int32Ptr',0);
  calllib('phidget21', 'CPhidgetInterfaceKit_create', devicePointer);
  device = get(devicePointer, 'Value');

The devicePointer is converted to the handle device as a handle for the Phidget. This example is specific to the Interface Kit because the call CPhidgetInterfaceKit_create is used. For another device, use the correspondingly named call in the C/C++ API.

The handle device is then used for all the C function calls where CPhidgetHandle phid is used in the C/C++ API. Every type of Phidget also inherits functionality from the Phidget base class.

Note that open() opens the software object, but not hardware. So, it is not a guarantee you can use the Phidget immediately.

The different types of open can be used with parameters to try and get the first device it can find, open based on its serial number, or even open across the network. The API manual lists all of the available modes that open provides.

Step Two: Wait for Attachment (plugging in) of the Phidget

To use the Phidget, it must be plugged in (attached). We can handle this by calling waitForAttachment. This function works for any Phidget. WaitForAttachment will block indefinitely until a connection is made to the Phidget, or an optional timeout is exceeded:

  calllib('phidget21', 'CPhidget_open', device, -1);
  if calllib('phidget21', 'CPhidget_waitForAttachment', device, 2500) == 0
     % Insert your code here
  end

Step Three: Do Things with the Phidget

MATLAB does not support event handling, so all data must be read and sent directly.

The most common thing you might want to do is read data from sensors. For example, in the code below, we might want to read data from a sensor on the Phidget Interface Kit.

Simply use the C API functions such as CPhidgetInterfaceKit_getSensorValue() or CPhidgetInterfaceKit_setOutState() for Interface Kits. The following reads and displays data from a sensor ten times as quickly as the while loop can execute:

  while n<10
    dataPointer = libpointer('int32Ptr',0);
    calllib('phidget21', 'CPhidgetInterfaceKit_getSensorValue', device, 0, dataPointer)
    disp(get(dataPointer, 'Value'));
    n=n+1;
  end

Step Four: Close and Delete

  calllib('phidget21', 'CPhidget_close', ikhandle);
  calllib('phidget21', 'CPhidget_delete', ikhandle);

At the end of your program, don’t forget to call close to free any locks on the Phidget that the open() call put in place!

The complete set of functions you have available for all Phidgets can be found in the C/C++ API. Note, however, MATLAB does not make use of the event functions in the C/C++ API

If you are looking for more information about a particular function, we provide that as well. You can find more description on any function either in:

1. Our API Overview which describes the set of calls common to all Phidgets, or
2. The Device API page for calls available only on your specific Phidget.

Common Problems and Solutions/Workarounds

Octave Problem: The function calls loadlibrary() and callib() are not supported in Octave

Likely Fix: As use of Phidgets in MATLAB requires these calls, the best is probably to choose a programming language that is not MATLAB. You can choose from many languages that we support.

However, this may not be possible if, for example, you already have a lot of external code written in MATLAB that you would like to interface your Phidget with. Here are a few suggestions to help you find a way to use your existing MATLAB code:

• Write your overall program in Python. Python natively controls Phidgets, and you can use Pytave to interface between the Python Phidget code and your Octave code.
• If you are using a version of Octave that Pytave does not support, write your program in Python as above. Then, you can try reading your matlab code through R, and using RPy to interface with Python.
• External foreign linking libraries (Swig, FFCall) might be made to work...

Mac OSX Problem: The function __stdcall does not exist outside Windows systems

Likely Fix: You can try defining __stdcall to be nothing, and this will simply call the Phidget functions in a raw manner rather than having the stack managed by the function itself. You can do that by adding the following to the top of your phidget21Matlab.h file:

  #ifndef WIN32 
  #define __stdcall
  #endif