Hardware-Software System for laboratory experimentation in electronic circuit

Transcription

1 Hardware-Software System for laboratory experimentation in electronic circuit J. JAIMES-PONCE, I. I. SILLER-ALCALÁ, R. ALCÁNTARA-RAMÍREZ AND J. SÁNDOVAL- GUTIÉRREZ Departamento de Electrónica, Grupo Control de Procesos Universidad Autónoma Metropolitana Av. San Pablo No. 180, Col. Reynosa Tamaulipas, Del. Azcapotzalco, C. P.0200, México D.F. MÉXICO Abstract: - Currently engineering students have access to a great deal of digital systems as support in their professional training, a very high percentage of students have access to personal computers, in contrast to access to equipment for experimentation with electronic circuits, which only available in laboratories, and in general, it is not economically feasible for a student. In this paper a system is developed, which combines a virtual application, which contains basic tools, such as voltage sources, pulse generator, voltmeters, digital switches and digital LED together with basic hardware that has instruments with basic functions, which help to conduct experiments on a personal computer. The system is based on a virtual application developed in Visual Basic, and hardware based on a microcontroller that communicates through a USB interface with a personal computer, and includes basic analog electronics, forming a very useful tool to access measuring system and directly carry out real experiments. Key-Words: - Engineering education, virtual laboratory, microcontroller, USB, analogue electronic 1 Introduction This work is focused on engineering students who require basic equipment for experimenting with electronic circuits. Usually practices are carried out in the laboratories of the institution, using greater or lesser extent laboratory equipment according to the level of electronics that are experimenting, but in general, the basic laboratory equipment is underutilized functions. For students in our public institutions is almost inaccessible to purchase equipment such as voltage sources, function generators, multimeters, etc. But the student could build your own team, not being a very portable solution, unless all integrated into a single system that would be a bit big to be transported. To be portable, a solution is to use virtual software, for example LabView with data acquisition cards that connect directly to the internal buses of personal computers, to acquire and process data, or to send information either digital or analog, or similar cards that are interconnected by USB port. Or a more specialized software applications like Matlab Simulink, GENIE, etc. Again, the cost is prohibitive for a student. The web-based solution for the experiments at universities takes a great interest due to the cost of the experimental laboratories at universities with a large number of students. Remote laboratories are a solution for provide students to access measuring system via Internet and directly carry out real experiments without their physical presence [6-9] and with a low cost. In this paper an alternative solution is presented, which consists of a system based on a virtual application developed in Visual Basic, and hardware based on a microcontroller that communicates through a USB interface with a personal computer, and includes basic analog electronics, forming a very useful tool to access measuring system and directly carry out real experiments. Since currently the virtual application development with Visual Basic, as well as development of electronic systems which can be connected with such software is relatively simple, in a first stage a compact system is developed, which has the characteristic of providing basic functions that are widely used in testing electronic circuits, Figure 1, for example, have three voltmeters in the range of 0 to 10 [V], generation of multiple frequencies square wave, PWM, for monitoring eight leds and eight digital signals switches to generate digital signals. These properties are monitored and controlled on the hardware developed with a virtual application. 2 System description Hard-Soft system provides a great advantage, portability, since the software is developed in Visual ISBN:

2 Fig. 1 Hard-Soft system Basic, and the hardware is based on a microcontroller, the PIC18F4550 which internally has a USB communication module. The system has characteristics that include: a) Virtual Application. b) Three Voltmeters in the range of 0 to 10 [V]. c) Variable power supply, with symmetric positive and negative voltage, 0 to + 12 [V] and 0 to - 12 [V]. d) Fixed power supply 5 [V]. e) Pulse Width Modulation. f) Pulses of 0.5, 1, 5, 10, 50, 100, 500 and 1000 Hz g) Eight virtual LEDs. digital Inputs h) Eight virtual switches. Digital outputs. i) Detection of short circuit in the power supply PCB dimensions are 10 x 12 cm; these dimensions together with the virtual application, allow use in any desktop computer, or a Lap Top into a room, laboratory, classroom, etc.., at any place where there is only one electrical contact. A feature of the virtual application is the development of own ocx controls, knobs, switches and LEDs, which gives personality to the software developed, Fig 2. Basically, the virtual application recognizes the hardware and connects to this, sending parameters that define the value of bipolar supply voltage, frequency of output pulses or pulse width variation as well as the reception of data, which indicate the virtual application, what is the status of three dc voltages, and / or digital input status. If a short circuit occurs in one of the power supplies, hardware reports the incident to the computer with the purpose of the user account and correct the cause of this. 3 System development 3.1 Software The virtual application was developed in Visual Basic, trying not to use common controls of this software, to give a distinct appearance to any application developed in this software, making a cover very similar to an real instrument to achieve this, we developed own controls. Only has a simple main menu, since the application does not require anything more complex, Fig 3. Fig. 3 Main Menu Voltmeter The system has three analog inputs in the range of 0 to 10 [V] to monitor three different voltages, referenced to ground. Fig 4. Fig. 4 Three voltmeters Fig. 2 Virtual front panel Generally, if there is only one voltmeter to monitor various voltages, it is necessary to make connections and disconnections, being disturbing if this is ISBN:

3 common, with this tool, is possible to monitor up to three voltages referenced to ground at the same time Power Supplies The system has three power supplies, one fixed 5 [V], and two symmetric variables in the range of 0 to +12 [V] and 0 to -12 [V]. These last are controlled with a virtual knob, Fig 5. In order to obtain the selected voltage value, it is necessary to activate the switch, which to change its position, virtual LED lights to indicate that it is enabled. Fig. 7 PWM Digital Inputs This option uses the PIC18F4550 Port B to capture and display digital data in virtual LEDs. Below each virtual LED there is a field with text "MARK" to write a name or character, which relates that led to the point where the test circuit, where the logic value is monitoring, Fig. 8. Fig. 5 Control of variable voltage power supply Pulse This function selects the frequency fixed values for pulses with TTL levels, which are 0.5, 1, 5, 10, 50, 100, 500 and 1000 Hz, which are used mainly for digital circuits, Fig 6. Fig. 8 Digital Inputs and LEDs Digital Outputs The Port E of the microcontroller is used in this tool, which has eight virtual switches with corresponding LED used to display, if the switch has a "logical one". It also has a field, where you can type a word or short identifier for linking with the point circuit under test, where a logic level voltage is introduced Fig. 9. Fig. 6 Pulses frequency TTL PWM PWM values have a fixed frequency of 1 khz, 10 khz and 50 khz. There are no values below 1 khz because the microcontroller PWM can not generate this option values below approximately 850 Hz, Fig 7. The way to get the different frequencies is from the main menu with the option PWM Conf. Fig 3. Fig. 9 Switch ISBN:

4 3.2 Hardware The hardware is developed based on the PIC18F4550 microcontroller, which has a number of internal modules that allow us to perform the functions described above; the most important for this application is the USB module which facilitates the communication with the computer without using a specialized integrated circuit. Timer to generate different frequencies, input/output ports, the PWM module for variable source option and Pulse Width Modulation. Analog electronics is also used for fixed and variable sources Microcontroller and USB PIC18F4550 microcontroller is a device that has 40 terminals, which together with internal modules allow a wide variety of applications. For this project, provides USB communication, since it is a direct physical connection to a computer or digital device, Fig 10. Fig. 11 Power Supply of 5 V Variable symmetric Power Supply This source provides the voltage values of 0 to 12 V and 0 to -12 V. In the design of this source the same configuration is used, except that the control signal is for both positive and negative sources. The positive supply is designed with an operational amplifier LM324, in noninverting configuration and NPN transistors. The negative supply is designed with an operational amplifier in inverting configuration and PNP transistors, Fig 12. Similarly, darlington transistors are used to enhance the current output of each amplifier and the transistor BC547 for positive source and BC557 for the negative, which are used as overcurrent protection elements. Fig. 10 PIC18F4550 microcontroller and USB connector Power Supply of 5 V The source of 5 V is designed entirely with analog electronics to have control over this, especially if you have a short circuit. One option is to use the 5V that provides USB connector; however, if not operated properly and produces a short, it would be doing directly on the computer, which is why we have chosen to implement this form. This source fixed and variable feed with a transformer, rectifier and capacitor as filter. As shown in the diagram, an operational amplifier LM324 is used and two transistors: TIP121 is used to enhance the current output of each amplifier and BC547 as overcurrent protection, Fig 11. Fig. 12 Variable symmetric Power Supply Voltmeter To implement the voltmeter with three inputs, three operational amplifiers in voltage follow configuration are used, as coupling stages with high impedance, Fig 13. As the voltage that can be measured is in the range of 0 to 10 V, a voltage divider is used in the output, to halve the maximum voltage which can vary between 0 and 5 V, thus the microcontroller achieves an appropriate conversion. ISBN:

5 Fig. 13 Coupling to the analog inputs Assuming that exceeds the input voltage of the operational amplifiers, to saturate this does not allow the voltage rises at the input of the microcontroller above 7V, coupled with this, the voltage divider resistors and the microcontroller's internal protection, protect this Input and Output Ports The Port B is used as digital inputs, and Port D is used as digital outputs, Fig. 14. These ports have the coupling resistance of 470 Ohms, which have the function of protecting the microcontroller if you accidentally connect the circuit at the output voltage of our system, or you accidentally connect one or more outputs of Port D at our system ground. Fig. 14. Digitals Input and outputs configurations 4 Conclusions The system developed in this work has proven very useful for a variety of experiments, where it is not required to use very specific functions of commercial measuring instruments or signal generation, especially in the testing and development of experiments with digital circuits. The portability makes it very attractive, since the virtual application has removed the physical volume and the cost of the displays, LEDs, knobs and switches control signals, which reduces system cost. With this development demonstrates the result of the synergy of software and hardware applied to develop projects. References: [1] Jan Axelson, USB Complete: The Developer s Guide, 4th Edition, Lakeview Research, [2] Jhon Hide, USB Design by Example, A practical Guide to Building I/O Devices, 2 nd Edition, Intel University Press, [3] Dogan Ibrahim, Pic Basic Projects: 30 Projects Using Pic Basic and Pic Basic Pro, Elsevier- Newnes, [4] Tim Wilmshurst, Designing Embedded Systems with PIC Microcontrollers, Principles and applications, 2 nd Edition, Elsevier Ltd, [5] Francisco Javier Ceballos, Enciclopedia de Microsoft Visual Basic, 2 nd Edition, Alfaomega and Ra-Ma, [6] J. Djordjevi c-kozarov, Remote Laboratory Development for the Education in the Field of Electronic Measurement, Scientific publications of the state university of Novi Pazar Ser. A: Appl. Math. Inform. and Mech. Vol. 1, No. 1, 2009, pp [7] Ouyang Yang and et al, Web-based Interactive Virtual Laboratory System for Digital Circuit Experiment, Innovations in E-learning, Instruction Technology, Assessment, and Engineering Education, Springer, 2009, pp [8] Dongsik Kim and et al, A Web-Based Virtual Laboratory System for Electronic and Digital Circuits Experiments, Hybrid Learning and Education, Lecture Notes in Computer Science, Vol. 5685, 2009, pp [9] Y. Bolea, A. Grau, Virtual laboratory for simulation and modeling systems in engineering degree: A sustainable approach, The 4th IEEE International Conference on E-Learning in Industrial Electronics (ICELIE), 2010, pp [10] Yu Hou and Fang Wang, Web-based virtual laboratory for mechanical engineering, The 5th International Conference on Computer Science and Education (ICCSE), 2010, pp ISBN: