Low Cost Small Antenna Measurement Tool Based on ATMega8535 Microcontroller PDF

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Low Cost Small Antenna Measurement Tool Based on ATMega8535 Microcontroller Muhammad Ammar Wibisono 1, Achmad Munir2 Radio Telecommunication and Microwave Laboratory School of Electrical Engineering and Informatics, Institut Teknologi Bandung, Indonesia 1 [email protected], [email protected] ...

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Low Cost Small Antenna Measurement Tool Based on ATMega8535 Microcontroller Muhammad Ammar Wibisono 1, Achmad Munir2 Radio Telecommunication and Microwave Laboratory School of Electrical Engineering and Informatics, Institut Teknologi Bandung, Indonesia 1 [email protected], [email protected] Abstract This paper presents a design of small antenna measurement tool based on AVR ATMega8535 microcontroller. The actuator system consists of stepper motor and servo motor for the position of antenna under test (AUT) on azimuth and elevation angle, respectively. Keypad and LCD display are used for user interface. The mechanical system applies elevation-over-azimuth configuration which consists of an arm, turntable and gear system. Keywords: antenna measurement, microcontroller, ATMega8535, stepper motor, servo motor

1. Introduction Low cost and easy-to-use small antenna measurement device is needed especially for educational purpose in the study of antenna and wave propagation, since the existing tool from some vendor that requires additional instrumentation device and software increases the complexity and makes the overall cost relatively expensive [1]. Therefore, to reduce the complexity and cost, the control system is simplified using AVR ATMega8535 microcontroller as the main controller unit (MCU) instead of PC. In this paper, the system design of small antenna measurement tool including hardware, software and mechanical construction is described. The hardware system is developed based on AVR ATMega8535 microcontroller. The design will be implemented for educational purpose in the study of antenna system.

2. A Brief System Description The overall system consists of user interface, main controller unit, azimuth/elevation controller, and mechanical system. The block diagram of system is shown in Fig. 1

Fig. 1 Block diagram of overall system of small antenna measurement tool The user assigns the desired azimuth and elevation angle from the keypad, while the LCD displays the current angle. MCU produces signals to drive the stepper motor via L298 dual H-Bridge IC [3]-[5], which activates the gear system and turntable to control the position of AUT at some azimuth angle. Hence to control the elevation angle, MCU directly sends pulse width modulation (PWM) signal to determine the angular position of servo motor’s arm [2].

3. Hardware System Design AVR ATMega8535 microcontroller provides some useful features as the MCU, e.g. basic I/O ports for interfacing with keypad, LCD, stepper motor, and 16bits PWM channels for servo motor control [2],[4]. The schematic of the hardware system shown in Fig.2 uses 16MHz crystal oscillator as the clock source. MCU drives the stepper motor via L298 dual H-Bridge IC. Two reverse-biased diodes are connected to each of the output pins of L298 for suppressing back emf generated by the coil of stepper motor [5]. The MCU directly controls the servo motor by giving PWM signals with 20ms period from PD4/OC1B pin. User interface in the system is implemented using alphanumeric 16x2 characters LCD and 4x4 keypad.

Fig. 2 Schematic of hardware system

4. Software System Design The program for the MCU handles all of the input/output process in the system. The working procedure of the software system can be described as follows. First, the MCU initialize the I/O ports, LCD and PWM channel. The user sets the initial elevation angle and calibrates azimuth angle, then sets the angle increment value for changing the azimuth/elevation angle. The user can vary the azimuth and elevation angle while the MCU displays the current angle. Figure 3 shows the flowchart diagram of the software system, based on procedures above.

Fig. 4 Mechanical construction design (unit in mm)

6. Conclusions The system design of small antenna measurement tool has been presented based on AVR ATMega8535 microcontroller which provides some advantages such as reduction on complexity and cost, and also makes the system more user-friendly. However, the system has some limitations in which the maximum weight of AUT depends on the maximum torque of the stepper motor. In addition, the precision of azimuth and elevation angle depends on the characteristic of the motors and the mechanical system fabrication.

References [1] C. A. Balanis, Antenna Theory, Analysis and Design, 3rd ed., New Jersey: John Wiley & Sons Inc., 2005. [2] D. V. Gadre, Programming and Customizing AVR Microcontrollers, New York: McGraw-Hill Companies Inc., 2001.

Fig. 3 Flowchart diagram of software system

5. Mechanical Construction Design Generally, the mechanical construction consists of a turntable, gear system, and an arm as illustrated in Fig. 4. The system construction uses elevation-over azimuth configuration. Most of these parts are made from white acrylic. The gear ratio value is 5:9 (20 to 36 gears) to scale the stepper motor step angle from 0.90 to 0.50.

[3] I. A. Wibowo, M. Zarar, K. Al-Amin, and Fazliana, “Control Systems of a Turntable and Antenna Positioning Device in an Open Area Test Site”, International Conference on Intelligent and Advanced Systems (ICIAS), pp. 1-4, 2010. [4] W. Weihong and X. Liegang, “Design and Implementation of a Control System using AVR Microcontroller”, International Conference on Image Analysis and Signal Processing, pp. 320-323, 2009. [5] Z. Yajun, C. Long, and F. Lingyan, “A Design of Elevator Control System Model”, IEEE International Conference on Neural Networks & Signal Processing, pp. 535-538, 2008....