COMPUTER APPLICATION AND MICROCONTROLLER SYSTEM DESIGN ON TEMPERATURE AND LIGHT SENSORS MEASUREMENT TOOL MODULE

Wilson Wiyatno1, Melisa Mulyadi2

Electrical Engineering Department – Faculty of Engineering

Atma Jaya Catholic University of Indonesia

e-mail: 1wilson.wiyatno@student.atmajaya.ac.id, 2melisa.mulyadi@atmajaya.ac.id

ABSTRACT

The experiment module for sensor testing in the Electronic Laboratory Electrical Engineering Department, Faculty of Engineering Atma Jaya Catholic University of Indonesia, Jakarta is not well integrated. The sensor output is not homogenous and there is no application to show the characteristic of the sensor. To solve this problem, a computer based sensors measurement tool module needs to be made. The sensor gives the output such as analog value to the microcontroller. Microcontroller receives the output with Analog to Digital Converter (ADC), then microcontroller send the digital value to computer using serial communication. The application based on C# programming language is made as user interface to the user. To know the input of the sensor, simple linear regression, a type of numeric method, is used to calculate the input of the sensor and to make the linearity between the input and the output. The testing of the results in computer show that the error rate system is small. After the input and the output have been known, the graphic can be made to show the characteristic sensor to the user.

Keywords: Analog to Digital Converter, Microcontroller, Serial Communication, C# programming language, Simple linear regression.

ABSTRAK

Modul praktikum untuk percobaan sensor di Laboratorium Elektronika Jurusan Teknik Elektro, Fakultas Teknik UNIKA Atma Jaya, Jakarta tidak terintegrasi dengan baik. Keluaran sensor tidak homogeny dan tidak ada aplikasi untuk menampilkan karakteristik sensor. Untuk mengatasi masalah ini, perlu dibuat modul alat ukur sensor berbasis computer. Sensor memberikan keluaran analog ke mikrokontroler. Mikrokontroler menerima keluaran tersebut dengan Analog to Digital Converter (ADC), setelah itu mikrokontroler mengirimkan keluaran digital ke computer menggunakan komunikasi serial. Aplikasi yang berbasis bahasa pemrograman C# dibuat sebagai tampilan antarmuka kepada pengguna. Untuk mengetahui masukan sensor, regresi linier sederhana, satu jenis metode numeric, digunakan untuk menghitung masukan sensor dan untuk membuat linierisasi antara masukan dan keluaran. Pengujian hasil keluaran di computer menunjukkan bahwa kesalahan system kecil. Setelah masukan dan keluaran sensor telah diketahui, grafik dapat dibuat untuk menampilkan karakteristik sensor kepada pengguna.

Keywords: Analog to Digital Converter, Mikrokontroler, Komunikasi serial, Bahasa pemrograman C#, Regresi linier sederhana.

I INTRODUCTION

The experiment module for sensor testing in the Electronic Laboratory Electrical Engineering Department, Faculty of Engineering Atma Jaya Catholic University of Indonesia, Jakarta is not well integrated. Sensors are not assembled on one module with a signal conditioning circuit, so that the students have difficulty during the experiment and in resulting the not homogenous data. Thus, the students cannot analyze the results and cannot understand well the purpose of the experiments. To solve this problem, a computer based sensors measurement tool module needs to be made. The monitor shows the measurement results in a chart form. Furthermore, the results can be processed and can be saved to know the characteristic of the sensor. The sensors module that will be made consists of temperature and light sensors. Design of this module will be done by two researchers. This paper shows the focuses of the second researcher: computer application and microcontroller system design.

II LITERATURE REVIEW

A. C# Programming Language

C# (is read C sharp) is an object oriented programming language. C# was developed by Microsoft as part of .NET Framework. C# language was built based on C++ language that is influenced by aspects or language feature which is included in other programming languages. The superiority of C# than other language are [8]:

1. Simple

Pointer has been removed from C#. The unsafe operation as direct access to memory is not permitted. There are no operators such as "::" and "->".

2. Modern

C# is based on thriving trend these days. C# is effective to build interopable, scalable, and light applications. C# supports add-on that can make each component integrated into a web service which can be called from any applications and any platform through internet.

3. Object Oriented

C# supports full encapsulation, inheritance, polymorphism, and interfaces. Int, float, and double are not object in Java language, but C# introduces a structure that enables a primitive type to be an object.

4. Type Safe

An unsafe operation like converting double to boolean cannot be done by C#. Compiler will automatically convert each value type of variable with zero and convert each reference type of variable with null. Index of array always begin from zero, and the limitation is noted. The types that produce overflow are always evaluated.

5. Interoperability

C# supports add-on on COM and windows application allowing to use limited pointer. User does not implement an unknown COM interface explicitly because the feature already exists. C# allows the user to use an unsafe code block. C# can use the component that was made by VB.NET or other programming language which supports .NET.

6. Scalable and Updateable

.NET introduces assembly which is a device that describe itself through manifest. Manifest shows the assembly identity, version, language, digital signature, etc. An assembly does not need to be registered into the windows registry. The update process does not need to be registered too as reg svr32.exe. This problem can be done by erasing the old data and copy the new one.

B. Microcontroller

A microcontroller is a computer system that is combined in one integrated circuit. Microcontroller consists of microprocessor, program memory (ROM), data memory (RAM), I/O, and other features. Some of microcontrollers have Analog to Digital Converter (ADC), PLL, and EEPROM.

Microcontroller that is used is ATMega16 made by Atmel. The specifications of ATMega16 are [3]:

1. It has working voltage on 4.5 volt – 5.5 volt.

2. It works on frequency 0 MHz – 16 MHz

3. It works on temperature -40oC – 85oC.

4. It has 32 programmable tracks I/O.

5. It has a 16 KB In System Programmable (ISP) Flash Memory with 10.000 times read/write ability.

6. It has a 512 bytes Electrically Erasable Programmable Read Only Memory (EEPROM).

7. It has a 1 KB Static Random Access Memory (SRAM).

8. It has 8 channels 10 bits Analog to Digital Converter (ADC).

9. It has 2 8 bits Timer/Counter and 1 16 bits Timer/Counter.

10. It has a Serial Peripheral Interface (SPI) and Two-wire Serial Interface (TWI).

11. It has a Programmable Serial USART.

12. The interrupts can be done by external and internal.

Microcontroller ATMega16 schematic Figure can be seen on Figure 1.

[pic]

Figure 1 Microcontroller ATMega16 schematic

Microcontroller ATMega16 has 4 I/O ports to support the its work. The 4 ports are:

1. Port A (PA.7 – PA.0) is a port that has Analog to Digital Converter (ADC) so that Port A can receive analog voltage input. If ADC is not used, so Port A functions as two ways 8 bits I/O port with internal pull-up resistor.

2. Port B (PB.7 – PB.0) is a port that functions as two ways 8 bits I/O port with internal pull-up resistor. Furthermore, Port B has special function.

3. Port C (PC.7 – PC.0) is a port that functions as two ways 8 bits I/O port with internal pull-up resistor. Furthermore, Port C has a special function.

4. Port D (PD.7 – PD.0) is a port that functions as two ways 8 bits I/O port with internal pull-up resistor. Furthermore, Port D has a special function.

5. The other pins are:

a. Vcc is supply pin.

b. GND is ground pin.

c. [pic] is reset input pin.

d. XTAL1 and XTAL2 are input pin for oscillator crystal that is used as clock.

e. AVCC is ADC supply pin.

f. AREF is ADC reference voltage pin.

ADC is one facility of the ATMega16 microcontroller that uses to change analog voltage input into 10 bits digital data. ATMega16 microcontroller has one ADC that is connected to 8 input channels, so it is necessary to use a multiplexer to choose the ADC input alternately. ADC has separate supply that is AVCC. This AVCC value does not have 0.3V difference voltage from VCC.

In general, ADC initialization process consists of clock decision process, reference voltage (AREF), conversion result data format, and reading mode. This initialization is done with setting ADMUX register (ADC Multiplexer Selection Register), ADCSRA (ADC Control and Status Register), and SFIOR (Special Function IO Register).

ADMUX functions are to ensure ADC reference voltage, to ensure conversion result format data, and to choose ADC input channel. ADC reference voltage is obtained from AVCC, and external reference voltage is obtained from AREF. ADC conversion result is saved on ADCH: ADCL register. Conversion result format that can be set is bit idle placement.

ADCSRA functions are to activate ADC facility, to start conversion and to determine ADC clock. SFIOR function is to set operation mode and ACD trigger source. There are 2 operation modes that can be used: single conversion mode and free running mode. On single conversion mode, 1 time ADC input voltage conversion is done, while on free mode running, conversion is done continuously.

C. Serial Communication

Serial Communication that will be used is Universal Serial Bus (USB). USB can be set to work on low speed or high speed. To work on high speed, D- pin should be given pull-up resistor on 3.3 volt. To work on low speed, D+ pin should be given pull-up resistor on 3.3 volt [8]. Figure 2 shows USB port pins.

[pic]

Figure 2 USB port

D. Calibration

Calibration is a process that forms the relation between the value showed by measurement tool and the standard value as measurement reference. Relation between physical scale input and signal output on sensor is calibration. In general, a sensor is calibrated by giving inputs which has been known and noting down every outputs from the sensors.

Calibration is done to detect conventional value deviation on measurement tool and to ensure the measurement results that are appropriate with national or international standard values. Calibration needs to be done on this measurement tools module so that the outputs of the sensors appropriate with the specifications and the measurement reference.

E. Numeric Method

Numeric method is a method to calculate the mathematic problem with approximate solution. Numeric method that will be used is simple linear regression. Simple linear regression is used to find linear equation y = a x + b so that the equation has residual sum of squares. Residual sum of squares is shown with Equation 1:

[pic] (1)

To calculate a and b values:

[pic] (2)

[pic] (3)

The slope of the curve depends on ‘a’ value. The ordinate value of the curve depends on ‘b’ value. The fitting quality depends on coefficient correlation. The fitting quality is good, if the coefficient correlation is greater than or equal 0.8. To measure the coefficient correlation in linear regression:

[pic] (4)

III SYSTEM DESIGN

The system is named SensGraph. The system design in this paper describes the system illustration, microcontroller & Analog to Digital Converter software design, computer software design, and numeric method design.

A. System Illustration

In general, the system is divided into 5 (five) main parts which are the sensors module, amplifier, microcontroller, serial communication, and windows application. Figure 3 shows the block diagram of SensGraph. This paper contains the focuses of the second researcher (marked by blue box).

[pic]

Figure 3 Block diagram of the SensGraph

After each sensor gives the output (focuses of first researcher), microcontroller receives the sensor output as an analog input in the ADC pin. Microcontroller converts the analog input into digital and sends the data to the computer. The microcontroller sends data to the computer using Universal Serial Bus (USB) communication. In this case, microcontroller is used to connect the transfer process from sensor module and the computer. Computer, with the Microsoft Visual Studio software, processes and saves the data. Computer gives a display menu of the sensors as option of the output. After the options are chosen then software will process the received data from the sensor module into a graphic view. The graphic shows the characteristic of each sensor. The graphic shows the relation between voltage and temperature or light intensity in Cartesian axis. The graphic can be saved into a computer file with special format so that the graphic can be seen whenever the users want to see.

B. Microcontroller Software Design

The programming language that is used on microcontroller is C# language and the software that is used is CodeVisionAVR. Figure 4 shows the flowchart of microcontroller software.
[pic]
Figure 4 Flowchart of the microcontroller Microcontroller waits the input from the computer to choose which sensors that will be measured. If there are the inputs from computer, microcontroller will read it using this listing code: unsigned char UART_getdata() { while ( ! ( UCSRA & ( 1