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Jayani Edirisinghe

on 28 April 2013

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The main goal of this project is to develop and implement a prototype of two-axis solar tracking system based on a PIC microcontroller. The parabolic reflector or parabolic dish is constructed around two feed diameter to capture the sun’s energy. The focus of the parabolic reflector is theoretically calculated down to an infinitesimally small point to get extremely high temperature. This two axis auto-tracking system has also been constructed using PIC 16F84A microcontroller. The assembly programming language is used to interface the PIC with two-axis
solar tracking system. The temperature at the focus of the parabolic reflector is measured with temperature probes. This auto-tracking system is controlled with two 12V, 6W DC gear box motors. The five light sensors (LDR) are used to track the sun and to start the operation (Day/Night operation). Time Delays are used for stepping the motor and reaching the original position of the reflector. The two-axis solar tracking system is constructed with both hardware and software implementations. The designs of the gear and the parabolic reflector are carefully considered and precisely calculated. PROPOSED DESIGN
There are two type of control system, open-loop
control system and closed-loop control system.Closed-loop
control system is used in this project and PIC16F84A is the
main controller and input and output devices are sensors
and DC gear box system.The proposed design in this project is
The procedure for implementing the whole system includes installing the parabolic reflector, choosing suitable design for gear boxes, and assembling the control circuit for the
system. Making a Parabolic Reflector out of a Flat Sheet The parabolic reflector is constructed with glass fiber plate. The easiest way is to cut and fold a flat sheet into a parabolic dish. Then a layer of glass fire is glued on its inner surface, for reflectivity.
The diameter of the parabolic reflector is about 2ft and its radius is about 1ft. So the radii of five concentric circles are drawn with the scales and the circles are divided by 6 uniformly spaced diameters. Each circle should consist of 12 identical sectors . Testing the Focus of the Parabolic Reflector A laser pointer can be used for checking the real shape accuracy of any “dish” reflector. Some dishes aren’t parabolic. So orthogonal (perpendicular) mounting the laser pointer to point directly into the dish and translating the laser long a rigid support, one can simulate parallel rays entering the dish. These can be reflected off the back of the dish and the focus movement observed. By translating the laser pointer from the rim of the dish towards the center (in at least two axes) the real upper limit of useable frequency for a particular dish can be measured. Using the laser gives a visible indication of the focus movement as the laser is translated. Some reflectors (dishes) aren’t parabolic and therefore the focus will move as the laser is translated. A true parabolic shape will have no movement of the focus. Most available dishes aren’t perfect but they can accurate enough for amateur microwave applications MECHANICAL DESIGN OF GEAR BOX SYSTEM Gears are used in the two-axis parabolic tracking system. Two DC motors are worm and worm wheel DC gearbox motors and the driver is used worm and the driven is used the worm wheel. It is used in the gear box motor because this position is more reduce the speed of the reflector than other gear system. The revolution of 12V, 6W DC motor is about 1908rpm. It can be measured by revolution counter. COMPONENTS AND OPERATION COMPONENTS AND OPERATION THE CONTROL SYSTEM In the control system, the important components are Light dependent resistor (LDR), LM 358 window comparator,TA7291PICs, BP139, TIP32, TIP31 ICs, and PIC16F84A microcontroller. Sensors Light dependent resistors (LDR) are used in the two-axis solar tracking system for detecting the dish position. Four LDRs are used for moving the altitude and azimuth of the reflector. Two sensors (East/West) are used in the altitude motion of the reflector and two sensors (Left/Right) are used in the azimuth motion of the reflector. These sensors are placed on the same
plane in two black pipes because sensors are sensitive the ambient light. A concave and convex mirror is placed at the top of the pipe for the light is falling on the centre of four LDR sensors. One LDR and 5kΩ variable resistors are joined and are connected to the 12Vdc power supply. This circuit is connected to 3rd LM358 and then the output of LM358 is connected to Pin 2 of 16F84A microcontroller. The whole circuit will start in the operation when the output voltage of light falling on this LDR is greater than 2.7V. The Light Dependant Resistor Cell Interface with the Microcontroller Two LM 358 ICs are used as a window detector (window comparator). In this project, the motor is ON when the output is below the set-point and OFF when the output is above the set point. ON/OFF action control is controlled with LM 358 window comparator shown in Figure . PIC 16F84A microcontroller is the main controller of the whole circuit and has many electronic circuits built into it, which can decode written instructions and convert them to electrical signals.

The first LM358’s Pin 1 and Pin 7 are connected to the RB0 and RB1 of PIC 16F84A and are used as the inputs of the 16F84A IC.

The second LM358’s Pin 1 and Pin 7 are connected to the RB4 and RB5 and are also used as the inputs of the 16F84A. These two LM358’s Pin 2 and Pin 5 are joined and connected to the outputs of two LDR sensors (East/ West) and two LDRsensors (Right/ Left sensor). The first and second LM358 is used as the window detectors.

The third LM358 is used as a comparator and this comparator is used the start of the two axis solar tracking system. Pin 4 and Pin 14 of PIC are connected to the 5V dc power supply and Pin 5 is ground. Pin 16 and Pin 15 are connected to the two 22pF capacitors and 4MHz crystal for clock frequency to orchestrate the movement of the data around its electronic circuits. RA0, RA1, RA2 and RA3 are the outputs of the 16F84A and these outputs are connected to Pin 5 and Pin 6 of two TA7291Ps. In this project, two TA7291P ICs are used for driving the DC motor. 12V dc power supply didn't really provide enough torque for the gear box motor to run smoothly. Finally, Darlington pair circuits are replaced between TA7291P IC and DC motor and are used for power amplifier. The circuits of two-axis tracking system are shown in figures PERMANENT MAGNET DC MOTOR CHARACTERISTICS PERMANENT MAGNET DC MOTOR CHARACTERISTICS A DC gear motor consists of a rotor and a permanent magnetic field stator and an internal gear box or gear head. The magnetic field is maintained using either permanent magnets are electromagnetic windings. DC motors are most commonly used in variable speed and torque applications TRACKING SYSTEM RESULTS In this project, for the reference voltage of third LM358 one LDR and variable resistor is supplied 5V dc but LDR does not sensitive the cloudy and lighting of the sky in this power supply. The output voltages of this circuit are not clearly difference between cloudy and lighting. So this power supply is changed to 12V dc power supply.
The resistances of 4-LDRs are not the same but are chosen nearly the same resistance. These sensors are placed on the same plane and at the side of the reflector. The Earth spins on its axis and completes one rotation in 23 hours 56 minutes and 4 seconds; this is a sideral day and is
slightly different from the familiar 24 hour day. It takes roughly 365 days for the Earth to go around the Sun once. Sun path is calculated by Javascript Solar Position Calculator for the year of
sun position .
The objective of PIC16F84A module is to sense from sensors and to control solar parabolic reflector. The parabolic reflector is placed to face the sun by manual before the experiment. And then this reflector to trace the sun the whole day until the reflector is touched the limit switches. CONCLUSION AND FUTURE WORK PIC (Peripheral Interface Controller) based system has various advantages; the electronic circuit components are less and cheaper than PC, portable hardware components, low power consumption rate, simple installation and operation. Besides PICis used that is cost effective and easy to maintain. So two axis auto solar tracking system is constructed based on PIC and it can be used in generating of electricity and domestic use. This system may be used for receiving always
maximum temperature at the focus of the reflector. The parabolic reflector is arranged with five LDR sensors for moving and changing place to face the reflector and the sun. Therefore the reflector is moving to face the sun to trace with two DC motors. These two DC motors are controlled with PIC16F84A under the programming of assembly language. The control of DC motor is more complex than the stepper motor but the stepping of DC motor is arranged with the gear system. This control is very simple, easier to design and less expensive to build. PIC 16F84A is used to control two DC motors accurately with minimum hardware at a very low cost. This project is also a trial and the mirror should be used
the surface layer of the reflector because it has the best reflectivity. Gear system can also be used other high quality motors and a small Stirling engine can be mounted at the focus of the reflector to produce the electricity to pump water.
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