# The Use of Wireless Networks and Mobile Applications in the Control of Electric Machines
## 3 Programming Environment for Prototyping a Mobile Application  
There are various technologies that enable the creation of mobile applications of high complexity operating on different operating systems and hardware platforms. Among them, the most popular are tablets and smartphones which are supported by Android or iOS systems. The article presents an application written in an environment designed for Android since it is a free and open-source operating system based on Linux [24; 25]. Authors have chosen MIT App Inventor because this platform gives engineers great opportunities to provide their projects' users with a modern interface. Simultaneously, this program offers a graphical interface that supports the work of an engineer ensuring an easy way of designing and programming applications as it uses Scratch programming language. The environment itself has many built-in functions that facilitate, for example, the handling of broadcasts or the visualization of content.  
The implementation of remote control of the power electronics converter requires the development of at least two types of programs. The former has to support a digital platform that is installed at the converter and directly transmits control signals to the power converter. In this case, the transmission based on Bluetooth and Wi-Fi is between a phase controller of a thyristor rectifier and software on a mobile device. The latter, however, is demanded by a mobile device. This one constitutes an application that is a graphical interface designed for a system user.  
In both versions of used drivers, the software for digital platforms has been written in the Arduino IDE environment as both Arduino UNO and NodeMCU v3 are compatible with it and have appropriate libraries. The programming of the above-mentioned digital platforms is not the subject of the article, therefore, only basic information has been provided [25].  
In this paper, authors bring the focus on the design and implementation of a mobile application developed for a DC electric machine supplied by a three-phase thyristor rectifier. Figure 4 shows the interface of this application, which consists of five views. It has been designed in MIT App Inventor and supports wireless transmission in Bluetooth and Wi-Fi technologies. The presented application is built on one screen, but depending on selected buttons, some of the widgets expire, and then the elements constituting another view appear. Such an approach is safer than scroll screens because all of the available options are within reach of a user, which is especially crucial in case of failure when access to a quick emergency shutdown of a motor is demanded [26; 27].  
The application's graphic is designed to provide safe, reliable and smooth control, which requires readily available options and quick response. Such an interface, unlike ones of the applications of general use, should not be extensive. Changing the motor rotational speed must be smooth, but at the same time take into consideration physical limitations, such as the inertia of the machine. Therefore, shifting the position of the slider, which results in speed change, occurs with a certain delay. In addition, there is a function to safely shut down the motor, which in most cases must take place with a certain delay in order not to lead to a sudden stop of the device that supplies the machine [26; 27].