DIDACTIC TOOL FOR PRACTICAL TESTING OF DIGITAL VOLTAGE GRADING APPLICATIONS l Renata 1. S. Pereira , Sandro C. S. Juca2
l
Federal University of Ceara, Fortaleza - Ceara, Brazil 2 Federal Institute of Ceara, Maracanau - Ceara, Brazil e-mail:
[email protected]@ifce.edu.br
Abstract
-
This
paper
and
implementation
programming
describes
the of
construction,
an
II. IMPLEMENTATION OF THE DIDACTIC SYSTEM FOR DIGITAL VOLTAGE GRADING
educational
embedded system made up of free educational software and
an
embedded
control
voltage for
electricity
laboratory.
Thus,
software
this
developed
of
sinusoidal
practices
in
work
and
power
presents
applied
to
alternating
The developed system can act in two ways: open-loop
electronics
control, as in the proposed gradation control voltage; or
educational
digital
control,
wirelessly via Bluetooth, to change the AC voltage of the
closed-loop with analog control of some variable such as, for example, temperature. These two forms of application are described in this topic.
grid using Android smartphones or tablets, making the
In order to implement the developed embedded system for
experiment more interactive and playful. The application
graduation by PWM, two applications will be shown: light
of
control of AC lamps
educational
verifying
the
software program
phenomena
and
development
and
in
experiments
change
stimulates consequently
influence
the the
logical
also in
allows
physical
and sinusoidal voltage control in
heating device.
reasoning
autonomy
of
the
A. Sinusoidal voltage grading in open-loop control
students that can raise hypotheses, make interferences in
When implementing the develop teaching tool in open
the programming and drawing conclusions from the
loop, a program in C language (firmware) was developed,
practical results obtained.
which must be recorded in the microcontroller circuit so that information from Android devices via Bluetooth could be
Keywords
-
Embedded system, Didactic tool, Free
received, such as smartphones or tablets, and vary the alternating voltage effective (AC) load via a digital circuit
Software, Digital Voltage Grading.
control. The communication process of the Android device to a load supplied by AC voltage is illustrated in Figure 1.
I. INTRODUCTION
Android
Embedded Microcontrolled System
Microcontroller embedded systems are very useful tools
�"
for the development of practices aimed at practical teaching power electronics [I] and, along with free software can contribute effectively in the teaching-learning process [2] [3]. Therefore, it is recommended, in the Brazilian National Curriculum Parameters, develop educational tools consistent with new teaching and learning methods compatible with current technologies [4]. Besides, this can awake vocations for technology careers in higher education [5].
lL
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AC digital control
Input 1101220 Vac
...
� i 1
Bluetooth
In alternating current teaching practices (CA), in which
Fig. 1. Illustration of the Bluetooth communication process between
you want to change the voltage value and effective load
an Android device and the microcontroller system for AC digital
current is usual the use of sinusoidal voltage drivers, also
control.
known as PWM (Pulse-Width Modulation) graders, Static Contactors or Controllers. In this context, this work describes the construction, the programming and the implementation of an educational system composed of
free educational software
and
an
embedded control system of AC sinusoidal voltage for electricity and power electronic practices in schools and universities laboratories. This system can act both in open and closed-loop. The communication of the experiments with free educational software can be performed via USB and using wireless communication protocols such as WiFi and Bluetooth [6].
To enable greater diffusion of the proposed educational software [7]-[8], a program (sketch) for communication with the Arduino platform, which can be accessed directly in the application educational software screen,
was developed.
Among other features, the application allows a certain PWM configuration of an experiment is stored in the application's permanent memory.
B. Android Educational software for Android devices This topic describes the operation of the application educational software called BT4SanUSB (2014) developed and available for free for Android devices on Google Play. This application developed for Android lets you control the
978-1-4799-8779-5/15/$31.00 ©2015 IEEE
variation of AC voltage via Bluetooth using the gradual disk on the application or through the on/off buttons. In Figure 2 the free educational software screens used in experimental physics also for composing real and virtual colors are shown. aD
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On
Off
Set1d L
Set1d 0
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Voice Recognition
ConfIgure BT name Download: BT4SanuSB.c
Bluetooth Modem:
Connect
r. --+----,-----1 - --+--.--t-----1
T
Thermocouples can measure a wide range of temperatures and can be replaced by other equivalents without introducing
GND
significant errors. Although practically it is possible to build a thermocouple with any combination of two metals, only those using a few standard combinations are used, that is because they have predictable output voltages to certain temperatures. One of the advantages of using thermocouples is that these generate theiw own voltage signal, i.e., excitation current are not requiered (that means there are no errors by self-heating). They are usually simple, robust, immune to vibrations and
Fig. 10. Pinout diagram and internal IC MAX31855 blocks.
Importantly,
the IC
MAX31855
uses
a
conditioning
circuit composed of an LC filter (inductive-capacitive) at the input and a buffer to 5 V voltage conversion (MCU supply voltage) to 3.3 V (supply voltage IC), as illustrated in the schematic of Figure 1 I .
The AD conversion results are read from the SO pin (serial
In this case, the mesh controller is a microcontroller with
data output), placing the CS pin (chip select) at low logic
PI control on the firmware; the actuator is the optoisolated
level and applying a clock signal SCK (serial clock input) as
TRIAC; the process is the heating resistive element and the
shown in Figure 12.
temperature sensor is a thermocouple, as shown in the
When the CS pin is at low logic level, the conditioning
diagram of the dynamic process in Figure 13. Reference is
circuit assumes the transmission status. Thus, any conversion
understood to be the input variable, i.e,
the controller
process is disabled. To start a new AD conversion of the
reference
to
thermocouple output
calculation.
analog
signal
to
four
bytes
it
is
necessary that CS pin is at a high logic level.
value
(desired
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GND
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value)
is
used
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