Home-Made PIC 16F877 Microcontroller-Based Temperature Control System for Learning Automatic Control KHAIRURRIJAL, MIKRAJUDDIN ABDULLAH, MAMAN BUDIMAN Physics of Electronic Materials Research Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132, Indonesia Received 20 February 2008; accepted 20 September 2008 ABSTRACT: A closed-loop temperature control system, which is composed of a thermal plant and a controller, has been developed to support undergraduate students in learning automatic control delivered in the Special Topics in Instrumentation Physics course. The thermal plant was made from a plastic box covering a lamp and a fan, which heats and drains the air in the plastic box, respectively, as well as a temperature sensor. The controller with a proportional control action was realized by employing the PIC 16F877 microcontroller. The control signal updates pulse-width modulators (PWMs) in which driver circuits turn on or off the lamp and the fan. A mathematical model of the closed-loop control system was derived and a theoretical transient response was then obtained. It is found that the experimental transient responses were always much lower than the set point and the steady-state errors were high for the proportional sensitivity (KP) lower than 10. For KP higher than 10, the transient responses tend to approach the set point to cause small steady-state errors. These characteristics are consistent with the theoretical transient response. Further examination revealed that the closed-loop system is a higher order system due to the action of the PWMs and the driver circuits. ß 2010 Wiley Periodicals, Inc. Comput Appl Eng Educ 19: 1017, 2011; View this article online at wileyonlinelibrary.com; DOI 10.1002/cae.20283 Keywords: control system; instrumentation physics; microcontroller; proportional; thermal plant
INTRODUCTION Control systems courses are traditionally offered by Electrical and Mechanical Engineering Departments [13]. Few departments outside electrical and mechanical engineering disciplines present courses on control systems in their curricula. Several Chemical Engineering Departments at several universities in USA have introduced modern control systems teaching to their undergraduate students [4,5]. The teaching of modeling, simulation, and control to students in the Department of Applied Physics, Faculty of Physics at the University of La Laguna, Spain, has been done [6]. School of Physics and Astronomy at the University of Nottingham in the United Kingdom has changed the curriculum of the second year practical laboratory course to implement Matlab in teaching undergraduate students about instrument control techniques [7].
Correspondence to K. Khairurrijal (
[email protected]). Contract grant sponsor: Ministry of National Education of the Republic of Indonesia. ß 2010 Wiley Periodicals Inc.
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Physics Study Program at the Faculty of Mathematics and Natural Sciences of Institut Teknologi Bandung offers some elective courses in the fourth year of undergraduate program. One of the elective courses is FI4172 Special Topics in Instrumentation Physics, which is a 3-credit unit course. It contains lectures on advanced instrumentation systems including instruments for characterizing materials, nuclear and biophysics instruments as well as instruments in geophysics because the Physics Study Program has several subprograms such as Physics of Electronic, Magnetic and Photonic Materials, Nuclear Physics, Biophysics, and Geophysics. A very important topic delivered in the course is automatic control because it is easily found in the instruments. In order to support theoretical concepts on automatic control that were explained by a lecturer in classroom, laboratory works that can be done by students must be provided. By executing the laboratory works, it is hoped that the students can learn the theoretical concepts easily and therefore grasp them more. This is reinforced by the survey done by Rickel [8], who found that students retain 25% of what they hear, 45% of what they hear and see, and 70% if they use the ‘‘learning-by-doing’’ method. A personal computer or microcontroller has been used in learning control with laboratory scale models [911]. Festo [12]
TEMPERATURE CONTROL SYSTEM
11
and Leybold [13] are the two leading companies in educational tools that supply various control systems for learning in laboratories of higher education. However, we have to spend more money for having the control systems because they are expensive. In order to reduce the cost, we built a control system. The controller was based on a PIC16F877 microcontroller because this microcontroller is easily obtained from the domestic market and popular among the undergraduate students. Noting that thermal process was learned in the second year when taking the Thermodynamic course, a thermal plant was selected to be controlled. In this paper, we report home-made temperature control system for learning automatic control. The hardware and software of the PIC 16F877 microcontroller-based temperature controller will be described. The thermal plant as a physical system is represented by a mathematical model. Experimental results obtained by applying the temperature controller to the thermal plant will be discussed thoroughly.
HARDWARE AND SOFTWARE OF TEMPERATURE CONTROL SYSTEM A process controlled by a controller in a closed-loop control system is schematically described in Figure 1. An input and an output of the closed-loop control system are a set point r(t) and a process variable y(t), respectively. The set point r(t) is the value to be reached by the process variable y(t), while y(t) itself is the variable to be controlled. A measuring element is used to quantify the process variable y(t). The output of measuring element z(t) is generally not the same as its input y(t). An error e(t) occurs due to the difference between the set point r(t) and z(t). The error e(t) is fed to the controller with a control action to result in a control signal u(t). Finally, the control signal is supplied to the process to influence the output y(t) [14]. The closed-loop control system given in Figure 1 has been realized by developing a home-made thermal plant and a PIC 16F877 microcontroller-based controller as shown by a photograph in Figure 2b. The thermal plant is very simple. It is a small plastic box enclosing air. The internal dimensions of the plastic box are 20, 6, and 6 mm in length, width, and height, respectively. The thickness of each side of the plastic box is 1 mm. In order to control the air temperature in the thermal plant, two actuators and a sensor are utilized. The actuators are a direct current (dc) lamp and a dc fan. The lamp acts as a heater to heat the air and the fan drains the hot air to the ambient. The sensor, which measures the air temperature, is located in the plastic box. As depicted in Figure 2a, the heart of the temperature controller is the PIC 16F877 microcontroller of Microchip Technology, Inc. It consists of a high performance and reduced instruction set central processing unit (RISC CPU), two pulsewidth modulators (PWMs), and a 10-bit analog-to-digital converter (ADC) [15]. Inputs of the temperature controller are a
Figure 1
Block diagram of closed-loop control system.
Figure 2 a: Block diagram of PIC 16F877 microcontroller-based temperature control system and (b) photograph showing plant and its controller. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
potentiometer and two buttons, which are employed to change a set-point temperature and other process parameters for a control action and to support system operation menu. As an output of the temperature controller, a 2 16-character liquid crystal display (LCD) [16] is used. The LCD therefore presents the set point and the measured plant temperatures as well as the process parameters. The PWM1 and PWM2 of the microcontroller are used to drive the actuators. Since currents provided by the PWMs are inadequate, driver circuits that turn on or off the lamp and the fan are required. The LM35 temperature sensor, which measures the air temperature in the plant, converts the measured temperature into voltage [17]. Noting that the maximum output voltage of the LM35 sensor is 1 V and the reference voltage of the ADC is 5 V, a signal conditioning circuit is needed to amplify the
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KHAIRURRIJAL, ABDULLAH, AND BUDIMAN
Figure 3
Characteristic of proportional control action.
maximum output voltage of the sensor. The RS232 serial communication of the controller is provided to send data to be processed in the computer. Considering that proportionalintegral-derivative (PID) control action is complicated to be implemented in the PIC 16F877 microcontroller, the proportional (P) control action was selected without reducing or neglecting the purpose of learning automatic control. The control signal u(t), which is generated by the P controller and illustrated in Figure 3, is mathematically given by Equation (1) [14]. 8 < Umax ; eðtÞ > emax uðtÞ ¼ U0 þ KP eðtÞ; emin < eðtÞ < emax ð1Þ : Umin ; eðtÞ < emin where Umax and Umin are the maximum and minimum values of u(t), respectively, U0 is the control signal when e(t) ¼ 0, and KP is the proportional sensitivity or the gain. Therefore, the P controller is essentially an amplifier with an adjustable gain. Additionally, the proportional band (PB) of the controller is defined as PB ¼
100 100% KP
ð2Þ
Figure 4 represents the flowchart of a program implemented on the PIC 16F877 microcontroller to perform a temperature control with the P control action. In the first step, the controller configurations are initialized and its functions are defined. Inputs of the P controller are the set point SP, which is the desired air temperature, the proportional sensitivity KP, and the permissible error A. They are set by pressing the two buttons and rotating the potentiometer as shown in Figure 2b. The next steps are to measure the process variable PV, which is the air temperature in the thermal plant, to calculate the error e(t), which is the difference between SP and PV, and to obtain the control signal u(t), which is the product of KP and e(t). The control signal u(t) updates the duty cycles of the PWMs in order to change the air temperature in the plant. If e(t) is highly positive, the lamp is turned on. The fan works when e(t) is highly negative. Otherwise, the lamp and the fan are alternately activated. Lastly, the error e(t) is compared to the permissible error A. If e(t) is still higher than A, then the proportional control action is repeated. Otherwise, the control action stops.
DESIGNING AND TESTING RESULTS OF CLOSED-LOOP CONTROL SYSTEM AND DISCUSSION The thermal plant built from a plastic box is schematically drawn in Figure 5. The plastic box confines a heater and air. The air
Figure 4 Flowchart of proportional control action.
temperature Ta is affected by heat Q(t) radiated by the heater and the ambient (atmosphere) temperature To. The plastic box temperature is Tb, which is due to the heat exchange between the air confined by the plastic box and the ambient air. The heat transfer rate due to the change in temperature of a material is written as [18] dQ dTm ¼ mm cm dt dt
ð3Þ
where mm and cm are the mass and the specific heat capacity of the material, respectively.
TEMPERATURE CONTROL SYSTEM
13
Assuming that the ambient temperature is constant, the thermal plant transfer function Gth(s) can be simply written as Gth ðsÞ ¼
Ta ðsÞ kðtz s þ 1Þ ¼ QðsÞ sðtp s þ 1Þ
ð11Þ
where k¼k
Figure 5
Model of thermal plant.
A heat transfer occurs from the air to the plastic box with the rate dQ ¼ A1 h1 ðTa Tb Þ dt
ð4Þ
where A1 is the contact area between the air and plastic box and h1 is the heat transfer coefficient from the air to the plastic box. By following Equation (3), the heat transfer rate of the air in the plastic box is dQ dTa ¼ ma ca dt dt
ð5Þ
where ma and ca are the mass and specific heat capacity of air. After substitution of Equation (5) into Equation (4), we obtain m a ca
dTa ¼ A1 h1 ðTa Tb Þ dt
ð6Þ
Since the heat transfer takes place between the air and plastic box as well as between the plastic box and the ambient, the heat transfer rate is given by dQ ¼ A1 h1 ðTa Tb Þ A2 h2 ðTb To Þ dt
ð7Þ
where A2 is the contact area between the plastic box and ambient, and h2 is the heat transfer coefficient from the plastic box to the ambient. Again, we have the heat transfer rate of the plastic box dQ/dt ¼ mbcb(dTb/dt) by following Equations (3) and (7) turns into mb cb
dTb ¼ A1 h1 ðTa Tb Þ A2 h2 ðTb To Þ dt
ð8Þ
where mb and cb are the mass and specific heat capacity of the plastic box, respectively. After rearranging Equation (8), the differential equation of the plastic box temperature is given as mb cb
dTb þ ðA1 h1 þ A2 h2 ÞTb ¼ A1 h1 Ta þ A2 h2 To dt
A2 h2 A1 h1 þ A2 h2
and
tp ¼
m b cb A1 h1 þ A2 h2
Noting that the mass densities of air and plastic box are 1.293 and 1.18 103 kg/m3, respectively, ca ¼ 1.006 103 J/ kg C, cb ¼ 8 103 J/kg C, h1 ¼ 5.6 W/m2 C, and h2 ¼ 0.039 W/ m2 C, the tz and tp are 1/(9.248 106) and 1/(1.1 103) s, respectively. Therefore, the zero is (9.248 106, 0) and the poles are (1.1 103, 0) and (0, 0) as depicted in Figure 6. Since the pole of (0, 0) is very close to the zero of (9.248 106, 0), then Gth ðsÞ ¼
k ðtp s þ 1Þ
ð12Þ
which is a first-order thermal system. It is shown in Equation (12) that the unknown parameters to be identified are k and tp. If the step input Q(s) ¼ A/s, where A is the amplitude, then the response gives Ta ðsÞ ¼
k A ðtp s þ 1Þ s
ð13Þ
The air temperature Ta(t), which is an inverse Laplace transform of Ta(s), is expressed as t Ta ðtÞ ¼ kA 1 exp ð14Þ tp In designing a closed-loop control system, we refer the system in Figure 1. The controller has the control signal u(t) in Equation (1). Assuming that the thermal plant input Q(t) is proportional to the control signal u(t), we obtain QðtÞ ¼ KPWM uðtÞ
ð15Þ
where KPWM is a constant due to the action of PWMs driver circuits. The Laplace transform of Equation (15) is then given by Q(s) ¼ KPWMu(s). Further assumption is that the transfer function of the measuring element (temperature sensor) H(s) is unity. This assumption is justified by the fact that the temperature measurement is performed in a narrow sampling time. This implies that H(t), which is the inverse Laplace transform of H(s), is a unit
ð9Þ
By substituting Equations (5) and (6) into Equation (9) and performing Laplace transformation, we obtain Equation (10) in which Ta(s) is the Laplace transform of Ta(t) Ta ðsÞ ¼ kðtz s þ 1Þ
QðsÞ To ðsÞ b b
ð10Þ
where A1 h1 mb cb ; tz ¼ and m2a c2a A2 h2 sðmb cb s þ A1 h1 þ A2 h2 Þ b¼ A2 h2
k¼
Figure 6 Zero and poles of open-loop transfer function Gth(s) in the complex plane.
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Figure 7
KHAIRURRIJAL, ABDULLAH, AND BUDIMAN
Block diagram of realized closed-loop control system.
impulse. Finally, the closed-loop control system in Figure 1 develops into that demonstrated in Figure 7. The closed-loop transfer function Gcl(s) is therefore given by Gcl ðsÞ ¼
Ta ðsÞ CðsÞGðsÞ ¼ TSP CðsÞGðsÞ þ 1
ð16Þ
where C(s) ¼ KP is the Laplace transform of u(t)/e(t) in Equation (1), and G(s) is the Laplace transform of the thermal process written as GðsÞ ¼
QðsÞ Gth ðsÞ ¼ KPWM Gth ðsÞ uðsÞ
ð17Þ
Using the thermal plant modeled by Gth(s) in Equation (12), Gcl(s) in Equation (16) becomes Gcl ðsÞ ¼
KPWM KP k tp s þ KPWM KP k þ 1
ð18Þ
Since the set-point temperature is B, TSP(s) ¼ B/s, the response of the closed-loop system in Equation (18) is KPWM KP k B ð19Þ Ta ðsÞ ¼ tp s þ KPWM KP k þ 1 s The air temperature as a function of time is then the inverse of Laplace transform of Equation (19). Finally, we obtain a ða þ 1Þt Ta ðtÞ ¼ B 1 exp ð20Þ aþ1 tp where a is given by KPWMKPk. It is shown that the ambient temperature Ta(t) approaches its steady state as time tends to infinity. The steady-state ambient temperature Ta(t ! 1) is Ta ðt ! 1Þ ¼
a B aþ1
Figure 8 Transient ambient temperature with various KP and set point of 808C. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
are not shown, their transient responses are similar to those for TSP of 808C. Their transient responses are always much lower than TSP as time rises for KP lower than 10. For KP higher than 10, on the other hand, their transient responses tend to approach TSP. These characteristics are expected as given by Equation (20). Further inspection of the curves in Figure 8 demonstrates some ripples on the transient responses. The measured transient responses differ from that in Equation (20). Again, by looking at Figure 8, it is seen that the steady-state air temperature Ta(t ! 1) does not reach the set-point temperature for small value of KP (KP ¼ 2). The values of KP that are higher than 10 result in Ta(t ! 1) coming close to TSP of 808C. These findings are predicted by Equation (21). It is also noticed that the steady-state error e(t ! 1) is high (around 118C) for KP ¼ 2. Furthermore, the steady-state error e(t ! 1) becomes smaller with increasing KP. These results are in agreement with Equation (22). In order to examine whether the thermal process G(s) shown in Figure 7 is a first-order system as assumed in developing the model, we plot jTa(t) Ta(1)j/jTa(0) Ta(1)j as a function of time on semilog paper by following Ogata [14]. The graphs are demonstrated in Figure 9. A first-order system gives a straight line with a negative slope [14], which is represented by the dashed line. It is clearly understood that the thermal process is not a firstorder system.
ð21Þ
Since KPWM and k are constants, the set-point temperature B is reached by increasing proportional constant KP so that the term a ¼ KPWMKPk becomes very larger than unity. The steady-state error e(t ! 1) is then written as eðt ! 1Þ ¼ B Ta ðt ! 1Þ ¼
B aþ1
ð22Þ
which turns into smaller as the proportional constant KP is increased. After designing the closed-loop control system, the system has been examined. The set-point temperature TSP was in the range of 4008C and the proportional constant KP varied from 2 to 60. The closed-loop transient responses with the set-point temperature of 808C are depicted in Figure 8. Although the closed-loop transient responses for other set-point temperatures
Figure 9 Graphs of jTa(t) Ta(1)j/jTa(0) Ta(1)j as a function of time. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
TEMPERATURE CONTROL SYSTEM
Further examination of the transient response curves in Figure 8 suggests that the thermal process is a higher order (more than second order) system because the transient response curves is the superposition of a number of exponential curves and damped sinusoidal curves with a particular characteristic of small oscillations superimposed upon larger oscillations and exponential curves [14]. Since the thermal process G(s) is a higher order system, it implies that the transfer function of the PWMs driver circuits Q(s)/u(s) is not a constant as expressed by Equation (15). As a result, the transfer function of the PWMs driver circuits is at least a second-order function.
FEEDBACK FROM STUDENTS The laboratory works on automatic control using the microcontroller-based temperature control system were initiated in the first term of the 20072008 academic year as a reinforcement to the theoretical lectures of the FI4172 Special Topics in Instrumentation Physics. As a basic assessment about the use of the microcontroller-based temperature control system, 20 students taking the course were required to fill out a questionnaire. Every statement in the questionnaire had to be answered on a five-point Likert scale with points 1, 2, 3, 4, and 5 representing ‘‘strongly disagree,’’ ‘‘disagree,’’ ‘‘neither agree nor disagree,’’
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‘‘agree,’’ and ‘‘strongly agree,’’ respectively. They gave their opinion on the following statements: a. I clearly understood the purpose and operation of the temperature control system before practicing with the microcontroller-based temperature control system. b. The microcontroller-based temperature control system helps a student to understand temperature control concepts. c. The practical exercises are easy to perform. d. I would like to have had extra time to do the laboratory works and to understand them better. Figure 10 shows questionnaire results for the four statements asked to the students. It was found that most of the students, formerly, did not have a good conception of the purpose and operation of the temperature control system as illustrated in Figure 10a. The results obtained from the second statement, in Figure 10b, indicate that the microcontroller-based temperature control system is an advantageous tool in achieving better understanding of temperature control concepts. As demonstrated in Figure 10c, most of the students found that the practical exercises are easy to perform. In addition, only 50% of the students would like to have had extra time to do the laboratory works and to understand them better as suggested by Figure 10d due to the credits assigned to the course.
Figure 10 Questionnaire results for the four statements given to the students.
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KHAIRURRIJAL, ABDULLAH, AND BUDIMAN
CONCLUSIONS We have developed a closed-loop temperature control system, which consists of a thermal plant and a proportional controller, for facilitating undergraduate students in learning automatic control. The thermal plant was constructed from a plastic box, which surrounds a direct current (dc) lamp, a dc fan, and a temperature sensor. The air in the plastic box is heated by the lamp and the heated air is drained to the ambient by the fan. The PIC 16F877 microcontroller was employed to realize the controller in which the control action was proportional. The control signal updates the PWMs of the microcontroller in which the driver circuits switch the lamp and the fan on or off with a certain time. A mathematical model of the closed-loop control system was derived by assuming that the thermal process is linear and a theoretical transient response was then obtained. It is found from the experiment that the transient responses were always much lower than the set point with increasing time for the proportional sensitivity lower than 10. For the proportional sensitivity higher than 10, on the other hand, the transient responses tend to approach the set point. These characteristics are expected by the theoretical transient response. Further examination of the transient response curves found that the thermal process in the closed-loop system is a higher order system (more than second order), and therefore, the transfer function of the PWMs driver circuits is at least a second-order function.
ACKNOWLEDGMENTS Partial financial support by the B Competitive Grant Program (Promoting Excellence) of the Directorate General of Higher Education, the Ministry of National Education of the Republic of Indonesia awarded to Physics Study Program, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung in 20062007 is acknowledged.
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[2] J.-S. Descheˆnes and A. Pomerleau, Process control through a case study: A mixing process. I. SISO case, Comput Appl Eng Educ 13 (2005), 324332. [3] Z. Kamis, E. E. Topcu, and I. Yuksel, Computer-aided automatic control education with a real-time development system, Comput Appl Eng Educ 13 (2005), 181191. [4] D. Mahoney, B. Young, and W. Svrcek, A completely real time approach to process control education for process systems engineering students and practitioners, Comput Chem Eng 24 (2000), 14811484. [5] T. F. Edgar, B. A. Ogunnaike, J. J. Downsc, K. R. Muske, and B. W. Bequette, Renovating the undergraduate process control course, Comput Chem Eng 30 (2006), 17491762. [6] L. Moreno, J. L. Sanchez, and L. Acosta, Experiments in modeling, simulation, and control by microcomputers, IEEE Trans Educ 34 (1991), 204208. [7] J. S. Sharp, P. M. Glover, and W. Moseley, Computer based learning in an undergraduate physics laboratory: Interfacing and instrument control using Matlab, Eur J Phys 28 (2007), S1S12. [8] J. W. Rickel, Intelligent computer-aided instruction: A survey organized around system components, IEEE Trans Syst Man Cybernet 19 (1989), 4057. [9] D. Ibrahim, Teaching digital control using a low-cost microcontroller-based temperature control kit, Int J Elect Eng Educ 40 (2003), 175187. [10] O. Gonza´lez, M. Rodrı´guez, A. Ayala, J. Herna´ndez, and S. Rodrı´guez, Application of PICs and microcontrollers in the measurement and control of parameters in industry, Int J Elect Eng Educ 41 (2004), 265274. [11] S. Postalcioglu, K. Erkan, and E. D. Bolat, Experimental control of chemical process for undergraduate student education, Proceedings of 1st WSEAS/IASME International Conference on Educational Technologies, Tenerife, Canary Islands, Spain, December 1618, 2005, pp 8386. [12] Festo Didactic Home Page. Available at www.festodidactic.com/ int-en/. [13] Leybold Didactic Home Page. Available at www.leybold-didactic. de/data_e/index.html. [14] K. Ogata, Modern control engineering. Prentice-Hall, New Jersey, 1997. [15] Microchip Technology Inc., PIC16F87X 28/40-Pin 8-Bit CMOS Flash Microcontrollers Datasheet, 2001. [16] China Optotech Co., Ltd., Specification for LCD Module ADT1620V02. [17] National Semiconductor Corp., LM35 Precision Centigrade Temperature Sensors Datasheet, 2000. [18] Y. A. C¸engel and M. A. Boles, Thermodynamics: An engineering approach, 4th edition, McGraw Hill, Boston, MA, 2002.
BIOGRAPHIES Khairurrijal received the BSc and MSc degrees in physics from Institut Teknologi Bandung (ITB), Bandung, Indonesia, in 1989 and 1993, respectively, and the DrEng degree in electrical and electronic engineering from Hiroshima University, Hiroshima, Japan, in 2000. He joined the Faculty of Mathematics and Natural Sciences, ITB, in 1991, where he is currently an associate professor of physics of electronic materials and devices. He is extensively involved in research on nanomaterials and nanodevices as well as electronics and instrumentation.
Mikrajuddin Abdullah obtained the BSc and MSc degrees in physics from Institut Teknologi Bandung (ITB), Bandung, Indonesia, in 1992 and 1996, respectively, and the DrEng degree in chemical engineering from Hiroshima University, Hiroshima, Japan, in 2002. In 1994 he entered the Faculty of Mathematics and Natural Sciences, ITB, where he is currently an associate professor of physics of electronic materials and devices. His research topics include nanomaterials and nanodevices as well as electronics and instrumentation.
TEMPERATURE CONTROL SYSTEM
Maman Budiman received the BSc degree in physics from Institut Teknologi Bandung (ITB), Bandung, Indonesia, in 1989 and the MEng and PhD degrees in physical electronics from Tokyo Institute of Technology, Tokyo, Japan, in 1995 and 1998, respectively. He joined the Faculty of Mathematics and Natural Sciences, ITB, in 1991, where he is currently an assistant professor. He performs research on optoelectronic materials and devices as well as electronics and instrumentation.
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