GUI application set up using QT designer. Sana Siddique. Team 5

Transcription

1 GUI application set up using QT designer Sana Siddique Team 5

2 Introduction: A very important part of the Team 5 breakout board project is to develop a user friendly Graphical User Interface that is able to display CAN voltages and module currents when the module are connected to the CAN voltages. The GUI need to take data from the Board and display it in real time. It also needs to have the capability to import this data in to a spreadsheet. This application note gives detailed information regarding creating GUI applications in Python with QT and also briefly describes the process of accessing data from COM ports. Overview: A different option to develop GUI for this project was to use the default python GUI package TkInter but that requires one to write the entire GUI code by hand. The simpler way to develop GUI applications is to use Trolltech's QT Designer which has a very user-friendly interface and generates the code for it using PYUIC. Firstly, before getting started, Python 2.x, PyQt 3.x and QT Designer 3.x packages need to be installed on your computer.

3 Figure 1: QT designer application After creating a new canvas you will have various options to create the interface. The line edit tool creates an edit box which is useful for taking user input. Since in this project we will require the user to input which modules are ON/Off and which ones are connected to CAN voltages, this tool will be used here. The listbox tool from the toolbar creates a listbox on the canvas and is used for storing the input from the user. The pushbutton tool creates a button on the canvas.

4 On clicking the button some information is sent to the method of an object. This method is referred as a slot. To connect a signal to a slot there is a connect tool available. There are various built in slots available for common functionalities of a button but there is also the option to create a customized slot to make the button to specialized tasks. To create a new slot (method), select Slots from the Edit menu. A dialog box listing custom slots will show up. Initially, it will be empty. Click New function to add new slots. Since we have a new slot now, it is ready to be connected to something. This is accomplished again using the same connection dialog box. To give this new method some functionality we will be required to write some python code. To implement the newly created method, in the Project Overview window in the top right-hand corner, double-click on the form1.ui.h file. A window will pop up showing the text of this file. All custom slots are implemented only in this file and then it can be directly included during the compilation process. This code can either be written in C++ or python. Python code is more difficult to write here because it is assumed that the code will be in C++ and the auto-indentation capability of QT designer doesn t always work out well with writing python code. So you are free to use another editor to edit your python code. All the slots are defined are methods of the dialog box, and all your widgets are objects within it.

5 Let s consider for an example that we need to retrieve the text from Line edit. It can be referred in the program by its name. It has a text() method which returns the object from the line edit. The ascii() method returns ascii string of entered text. e = self.lineeditname.text().ascii() Example 2: To add this text into the list box we should use the insertitem() method. self.listboxname.insertitem(e) Example 3: Finally, if you want to clear the line edit you should do the following: self.lineeditname.clear() Now we need to open up a shell. We want to compile our GUI code into Python code. This is done for us by the pyuic compiler. Pass the.ui file as an argument, and it will generate Python code onto standard output. This python code generated is the code for the GUI and the application is now ready for use. We are using pyserial to be able to access various I/O ports on the BeagleBone for the project. PySerial provides backend scripts for Python running on Windows, Linux,.NET and Mono. The module named serial automatically selects the appropriate backend. It provides support for different byte sizes, stop bits, parity and flow control. We selected this library because it is compatible with

6 python I/O library. pyserial includes a small console based terminal program called Miniterm this makes testing very easy. Conclusion: Using QT designer and pyserial we are able to achieve the entire functionality of the interactive User Interface and also read the data that is being sent by the modules and the CAN bus to the microcontroller. QT designer is a very easy to use, convenient toolkit which reduces writing tedious GUI code. Although, for the functionalities that are to be implemented on this project writing slots is necessary.

7 Bibliography: