How to make a GUI for USBCNC with Qt4 - Femtotech

How to make a GUI for USBCNC with Qt4 

Summary 

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femtotutorial 

Summary .................................................................................................................................................................... 1 

1 Preface ................................................................................................................................................................ 2 

2 Getting started .................................................................................................................................................... 3 

2.1 Prerequisites ............................................................................................................................................... 3 

2.2 First steps .................................................................................................................................................... 3 

3 The USBCNC SDK ................................................................................................................................................. 5 

3.1 Adding the library to the project .................................................................................................................. 5 

3.2 Including headers ........................................................................................................................................ 5 

3.3 The USBCNC Server...................................................................................................................................... 6 

3.4 Useful functions........................................................................................................................................... 7 

4 A complete example............................................................................................................................................ 9 

4.1 Design the GUI ............................................................................................................................................. 9 

4.2 Do it yourself ............................................................................................................................................. 11 

5 Deploy your application .................................................................................................................................... 12 

6 Links .................................................................................................................................................................. 12 

Revision A, 05-feb-2012

1 Preface 

This tutorial will guide you through all the steps needed to setup the developing environment, configure the project 

and write a small GUI for the USBCNC software. Using GUIs is a powerful way to extend the functionality of your CNC 

machine. You should customise your preferred tasks or create a user interface that meets some unusual 

requirements. 

As we will see later, interfacing with USBCNC is very easy and requires only some basic knowledge of C++ 

programming and of the Qt4 environment. Anyway, at the end of the document there are a couple of links to generic 

tutorials about Qt4. 



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2 Getting started 

2.1 Prerequisites 

To develop our applications for USBCNC we need some prerequisites: 

A computer with a Windows O.S. (here Windows 7) 

USBCNC Software by Bert Eding (http://www.edingcnc.com/index.php?pagina=8_download) 

USBCNC SDK, included in the USBCNC folder 

QtSDK for Windows by Nokia (http://qt.nokia.com/downloads) 

Some C++ programming experience and a minimum knowledge of Qt4 

Download and install both software. 

For this tutorial let’s assume that QtSDK was installed into C:\QtSDK and USBCNC into C:\Program Files 

(x86)\USBCNC4. Please, mind the difference between your actual installation paths. 

2.2 First steps 

Now we are going to check the functionality of the software we have just installed. Launch USBCNC4 and click on the 

START button in the middle of the screen. If you have not purchased the USBCNC CPU board yet, the application will 

run in Simulation mode: 

It is enough for testing purposes. Press F1 to enable drives and try to move around the screen using cursor keys. You 

should see the coordinates changing. Leave the USBCNC4 open, we need it in a while. 

Ok, now launch Qt Creator so that we can create a 

test project. In the Welcome window click on 

Create Project, then select Qt Widget Project > Qt 

Gui Application: 



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The next window will ask for a project name and the location path. At this point, we need to check the Target Setup: 

Usually, there is no need to change default values. Qt Creator will compile with the latest Qt Version and will place 

the executable files in either debug or release subfolder. Click Next on subsequent windows until the wizard ends. 

You should see the mainwindow.cpp default code: 

Please take time to become familiar with the environment. In the left lower side of the screen there are two play 

buttons. Click on one of them 1 and our empty application should run without problems. Close the application 

window using the X button. 

We are ready to develop new GUIs for USBCNC! 

1 The play button with a bug on the top is used to start debugging. 



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3 The USBCNC SDK 

The USBCNC SDK is provided with the USBCNC software. In the installation path there is a cncapi folder which 

contains all the necessary files: the library and the related headers. 

3.1 Adding the library to the project 

The first operation we have to do is to convey to Qt Creator that we want to use the USBCNC SDK. Double-click on 

the .pro file and edit according to the following picture: 

3.2 Including headers 

We have just configured our project to link the cncapi library. If we want to use the functions provided, we also need 

to include the header files. Open the mainwindow.h file and add at the beginning the #include instruction for 

cncapi.h: 



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The typedef is needed because the cncapi uses the integer type _int64 which Qt4 does not know. Now build the 

project (Ctrl + B or click on the hammer icon in the lower left). You should get no errors but a lot of warnings which 

are due to the syntax used by the cncapi. However, we may ignore them. 

Now let’s see how to do something useful with the USBCNC SDK. 

3.3 The USBCNC Server 

On launching the USBCNC software (this standard can be called GUI), a process will run in background: it is the 

CncServer.exe. In order to work properly, the standard GUI and all other GUIs, that we can build, have to be 

connected to this server. 

Open the mainwindow.ui form, drag and drop a Pushbutton and a Line Edit widgets and set the following properties: 

Pushbutton 

objectName btnConnect 

text CONNECT 

Line Edit 

objectName txtServerStatus 

readOnly true 

At the moment we do not use any layout, but we will come back to this topic later. 

Open the mainwindow.h and add the following code in the class definition: 

private slots: 

void on_btnConnect_clicked(); 

At this point, add the implementation in the mainwindow.cpp: 

void MainWindow::on_btnConnect_clicked() 

{ 

CNC_RC rc = CncConnectServer(""); 

ui->txtServerStatus->setText(CncGetRCText(rc)); 

} 

The “on_” prefix allows to connect automatically a signal (clicked() in the example) to the slot declared. In this way 

on clicking the pushbutton, the on_btnConnect_clicked() function is called. 

CncConnectServer() is the first cncapi function that we use. In order to know something more about any cncapi items 

just place the cursor on and press F2. The editor will show the definition in the header file. CncConnectServer() takes 

one optional argument: the .ini file name. You should pass this parameter only for stand-alone applications which 

will run without USBCNC4 software. In our example we have already the server running because the USBCNC4 



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software is still open, so we pass an empty string. 

As this is a key point, I have decided to summarise the options we have: 

If you want to create a stand-alone application: 

Call CncConnectServer(“cnc.ini”) 

Do not launch USBCNC4 but only your application 

If you want to create an additional GUI that runs beside the standard GUI: 

Call CncConnectServer(“”) with an empty string 

Launch USBCNC4 before your application 

Call CncDisconnectServer() before exiting 

In order to see the differences, you should try both ways with our simple example. The text box will show the 

messages returned from the function. 

3.4 Useful functions 

In order to learn more about the api provided by the SDK, you should explore yourself the cncapi.h. However, here is 

provided a list of the more common functions. 

CNC_RC CncConnectServer(char *iniFileName); 

As I have already said, this is the first function you have to call when connecting to the server. If no valid 

argument is passed, the server is already running; otherwise, it will be started. 

CNC_RC CncDisConnectServer(void); 

Call this function only in case you have started the server (you passed the “cnc.ini” to CncConnectServer). 

CNC_IE_STATE CncGetState(void); 

This is useful in order to know the state of the machine: ready, running a job, etc. 

CNC_RC CncPauseJob(void); 

This is useful to pause a job without abort. In this way, the motors do not lose steps and homing is not 

required. 

CNC_RC CncRunOrResumeJob(void); 

This is used to start a job or resume the paused one. 

CNC_RC CncRewindJob(void); 

This is used to rewind the job to the beginning. 



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CNC_RC CncReset(void); 

This function recovers from errors, exits from a paused state, establishes a connection with the server in 

case this has not been done yet. 

CNC_RC CncLoadJob(const char *fileName, 

int *jobFileLength, 

int *macroFileLength, 

int *isLongJob, 

int *isSuperLongJob, 

__int64 *sizeInBytes); 

Loads the job specified by the first parameters. All the others are output arguments, so pass the pointers to 

the local variables. If your application runs beside the standard GUI, call CncStartRenderGraph() to update the 

rendering window. 

CNC_RC CncRunSingleLine(char *text); 

Runs a line of G-Code or calls a subroutine contained into the macro.cnc file. 

double CncGetWorkPos2(int axis); 

Returns the position of the axis specified. Axes are defined in the cnc_types.h as CNC_X_AXIS, CNC_Y_AXIS 

and so on. Thus, to get the position of the Z axis simply call: CncGetWorkPos2(CNC_Z_AXIS). 



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4 A complete example 

Now we are ready to develop a complete application that provides basic features like the following ones: 

Displaying current coordinates 

Homing the machine 

Loading a job 

Starting / resuming / rewinding the job 

4.1 Design the GUI 

Open the mainwindow.ui form and add the necessary widgets: 

Play with the properties to see their effects. 

Now let’s write some codes. In order to read the current position, we need a timer that periodically calls the 

CncGetWorkPos2() function. To load a job we use the standard file dialog. For this first test I recommend you to run 

the application beside USBCNC4 so that you can see what is going to happen. 

To layout properly the widgets, put them first into a container (e.g. Group Box), then use the Lay Out on a Grid 

command. The same applies to lay out the containers in the form. 

This is the mainwindow.h code: 

#ifndef MAINWINDOW_H 

#define MAINWINDOW_H 

#include 

#include 

#include 

typedef qint64 _int64; 

#include "cncapi.h" 

namespace Ui { 

class MainWindow; 

} 



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class MainWindow : public QMainWindow 

{ 

Q_OBJECT 

public: 

explicit MainWindow(QWidget *parent = 0); 

~MainWindow(); 

private: 

Ui::MainWindow *ui; 

QTimer *timer; 

private slots: 

void on_btnConnect_clicked(); 

void on_btnLoadJob_clicked(); 

void on_btnStartJob_clicked(); 

void on_btnRewindJob_clicked(); 

void on_btnHomeAll_clicked(); 

void on_btnPause_clicked(); 

void on_btnReset_clicked(); 

void timer_ovf(); 

}; 

#endif // MAINWINDOW_H 

This is the mainwindow.cpp code: 

#include "mainwindow.h" 

#include "ui_mainwindow.h" 

MainWindow::MainWindow(QWidget *parent) : 

QMainWindow(parent), 

ui(new Ui::MainWindow) 

{ 

ui->setupUi(this); 

timer = new QTimer(this); 

timer->setInterval(100); 

connect(timer, SIGNAL(timeout()), this, SLOT(timer_ovf())); 

} 

MainWindow::~MainWindow() 

{ 

//CncDisConnectServer(); 

delete ui; 

} 

void MainWindow::on_btnConnect_clicked() 

{ 

CNC_RC rc = CncConnectServer(""); // ("cnc.ini"); 


if (rc == CNC_RC_OK || rc == CNC_RC_ALREADY_RUNS) timer->start(); 

} 

void MainWindow::on_btnLoadJob_clicked() 

{ 

QFileDialog *dialog = new QFileDialog(); 

QString file = dialog->getOpenFileName(this, "Select job", "", "CNC Files (*.nc *.cnc *.ngc *.gc *.iso 

*.tap)"); 

if (file.isEmpty()) return; 

int jobFileLength, macroFileLength, isLongJob, isSuperLongJob; 

qint64 sizeInBytes; 

QByteArray fileName = file.toLocal8Bit(); 

CNC_RC rc = CncLoadJob(fileName.data(), &jobFileLength, &macroFileLength, &isLongJob, &isSuperLongJob, 

&sizeInBytes); 


CncStartRenderGraph(1, 1); 

} 

void MainWindow::on_btnHomeAll_clicked() 

{ 

CNC_RC rc = CncRunSingleLine("gosub home_all"); 


} 

void MainWindow::on_btnRewindJob_clicked() 



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{ 

} 

CNC_RC rc = CncRewindJob(); 


void MainWindow::on_btnStartJob_clicked() 

{ 

CNC_RC rc = CncRunOrResumeJob(); 


} 

void MainWindow::on_btnPause_clicked() 

{ 

CNC_RC rc = CncPauseJob(); 


} 

void MainWindow::on_btnReset_clicked() 

{ 

CNC_RC rc = CncReset(); 


} 

void MainWindow::timer_ovf() { 

ui->txtX->setText(QString::number(CncGetWorkPos2(CNC_X_AXIS), 'f', 3)); 

ui->txtY->setText(QString::number(CncGetWorkPos2(CNC_Y_AXIS), 'f', 3)); 

ui->txtZ->setText(QString::number(CncGetWorkPos2(CNC_Z_AXIS), 'f', 3)); 

} 

4.2 Do it yourself 

The application we have just built is very simple and does not have all the features you can require. Try to add them 

yourself. For example, extending the monitoring of the position to all 5 axes, providing a function in order to move 

the tool to a known and safe position (hint: use CncRunSingleLine() using G0 code), etc. 



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5 Deploy your application 

The Qt Creator environment takes care of all the dependencies needed to run our application. When we want to 

launch the executable outside the Qt Creator, we have to copy them to the output folder or set the environment 

PATH variable. 

Before starting to deploy the application, we recompile it in Release mode. You find this option just above the two 

green play buttons. Run the application to check that everything works again. 

Now we can close Qt Creator and open the source folder, in our example C:/Tutorial/Test01. You see two folders 

called Debug and Release. Open the latter and you find the Test01.exe. If you try to execute it, it is likely you will get 

some errors about missing dlls. This is because the executable does not know where they are placed. 

I prefer to copy the dlls into this folder rather than set an environment variable. You need the following files: 

C:/QtSDK/Desktop/Qt/4.7.4/mingw/bin/QtGui4.dll 

C:/QtSDK/Desktop/Qt/4.7.4/mingw/bin/QtCore4.dll 

C:/QtSDK/Desktop/Qt/4.7.4/mingw/bin/libgcc_s_dw2-1.dll 

C:/QtSDK/Desktop/Qt/4.7.4/mingw/bin/mingwm10.dll 

C:/Program Files (x86)/USBCNC4/cncapi.dll 

Now the exe should run without problems. 

6 Links 

http://qt.nokia.com/learning 

http://zetcode.com/tutorials/qt4tutorial/ 



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How to make a GUI for USBCNC with Qt4 - Femtotech

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