As long as the sun shines, there is no death for solar energy. The solar energy is available in large amounts and also free of cost, this evokes more interest in the usage of this energy. Solar energy has many uses in our day to day life; it can be used to produce electricity using photo-voltaic cells. The process of converting solar energy into electricity is called as solar power. The solar energy can also be used for heating and cooling buildings with help of solar chimneys. Over the days many technologies have been developed to harness solar energy.
The future trend is alternative energy; most of the technologies developed today are related to alternative energy directly or indirectly depending on solar energy. Solar energy is very vital to support life on earth. Heat and light from sun along with the other renewable sources of energy such as hydropower, geothermal and wind power, if effectively used, can be very useful to mankind.
Usage of solar energy makes us dependent on renewable sources of energy. Since solar energy is available at free of cost, we do not need to spend money on non-renewable sources of energy. This factor contributes to invest in developing of different technologies to harness solar energy.
Solar energy has many applications ranging from house hold uses to industrial manufacturing. Solar energy can also be used in fields like transportation and agriculture sectors. Over the period of time many technologies have been developed for the different ways to harness the solar energy. The availability of solar energy in large amounts makes it even more useful and can be use in various applications from small to large photo voltaic plants.
General Statement of the Problem
In order to generate solar power in an optimal fashion, solar panels that are used to capture sun's rays need to be rotated based upon the movement of the sun. The existing solution for rotating solar panels use a rotation system that is based on time of the day and that is very specific to the location of the system. Figure 1 shows the basic diagram of the solar tracker. Some of the systems also use a GPS (Global Positioning System) to point the location of the installation of the system. These kind of systems are complicated to build and give results for all the geographical locations (We need a GPS for location and a microcontroller for adjusting the rotation co-ordinates based on the GPS output) as direction of sun's rays and movement of the sun varies from one location to other. The problem faced by most of these implementations is that they are too complex to be reproduced in large quantities. Innovative engineering ideas need to be developed to build a simple system that can be built cost effectively but still serves the purpose of maximizing solar energy.
To achieve more robust implementation with maximal efficiency and reproducibility on large scale, a system that takes feedback from the direction of the sun by using two light sensing diodes is proposed. These diodes convert light energy to electrical signals that are ultimately read by the microcontroller, which can be seen in Figure 2.
Figure 1. Basic Diagram of Solar tracker
Microcontroller uses a stepper motor to turn the solar panel by the required angle. The proposed system is simple since it does not need GPS, accurate Real Time clocks or manual intervention.
The comparison between exiting implementations and implementations with light sensor reveals lots of advantages of the later. The electronic system is simple to build as we need a microcontroller and some supporting circuits. We also use the concept of negative feedback to fine tune the direct on of rotation of solar panel .The system can correct significant errors in the electronic system that generally occur due to voltage fluctuations and aging as we have negative feedback to tell us if we reach optimal position. The proposed system also has the additional advantage that it does not need to take into consideration the latitude at which system is installed (northern latitudes will need more southern tilt if not for auto correction of direction). Thereby it frees up any engineering time required for custom installation.
Objectives
This project seeks to explore a simple, cost effective, robust solution to adjust the panels using sensors, 555 timer, microcontroller and stepper motor. The idea behind this proposal consists of two photo transducers that collect light from two different positions on the solar panel and converts this light to analog voltage. The 555 timer converts this voltage to digital format which can be fed to the microcontroller. The microcontroller can take inputs from two sensors and decide if we are collecting maximum light or we need to change position.
MICRO CONTROLLER
Power Supply
SOLAR PANEL
LDR
LDR
ULN
STEPPER MOTOR
555 TIMER
555 TIMER
Figure 2. Pictorial Representation of solar tracker.
Limitations
The limitations of this implementation include the proposed system is not able to sense light in a cloudy environment. This should not be a major limitation since light collection during a cloudy day is at minimum. There might be some maintenance needed to make sure that sensors are not covered by dust and block the light. Some of these limitations can be overcome by having a backup Real Time Clocks based system.
Definition of Terms
Power Supply: Voltage regulated power supply supplies power to all the electronics. This is generally off-the- shelf linear regulator that outputs supply voltage required by all the electronics while filtering out any supply variations.
Input Photo Transducer: Sensor that converts light to electric signals which can be processed by on board electronics is a photo transducer.
555 timer: All real world signals are analog with some noise. 555 timer as Schmitt trigger removes unwanted noise and convert them to digital signal.
Microcontroller: This is digital processing engine that is at the heart of the system. It takes digital signals from 555 timer and gives the output to stepper motor to turn in the right direction.
Stepper Motor: Mechanical element that turns the solar panel direction.
Assumptions
1. There is an ever increasing need for solar power.
2. Solar panels are needed to generate electricity from sun.
3. Solar panels need to orientate in the direction of sun to capture maximum Sunlight.
4. Best of capturing maximum sunlight is have light sensing photo transducer.
Chapter-2
A review of Related Literature
Overview
The first ever automatic solar tracking system was presented in 1975 by Mcfee, who developed an algorithm to compute total received power and flux density distribution in a central receiver solar power system. The effect of mirror's wavy curvature and also the determination of tracking error of plane mirror heliostats in a rectangular array around a central receiver of the solar power system can be obtained by dividing the single mirror into 484 parts, and then summing the contribution of all the mirrors. Flux density and total power received from the sun for a given location were calculated, including the shading effects and blockage of adjacent mirrors. The heliostats were assumed to be mounted according to altitude-azimuth values (McFee, 1975).
In the 90s, Maish developed a control system called Solar Trak, which provided sun tracking, communication, night and emergency storage and control functions to drive one and two axis trackers manually. It has comparatively better system reliability and accuracy as its control algorithm has self alignment routine and self adjusting motor actuation time. Its full day experimental results showed accuracy of better than +0.1 (Maish, 1995). Kalogriou(1996) proposed a solar tracking system that used single axis solar concentrating systems and was mainly suitable for parabolic collectors with good concentration ratios. This system was made up of Light dependent resistors (LDRs). The LDRs detected the position and status of the sun. Kalogriou used three LDRs: ï¬rst to detect the focus of the collector, the second to detect the cloud cover and the third to sense day or night. The LDRs generated an electrical signal that was fed to a D.C. motor (12V), which operated at a very low speed. A speed reduction gear box was used, which helped in rotating the collector (Kalogirou, 1996).
Open Loop Architectures
In 2004, Abdallah and Nijmeh designed an electromechanical, two axes sun tracking system with an open-loop algorithm and enhanced it by using Programmable Logic Controller (PLC) for controlling the tilt, motion and position of solar panels. This system used two separate motors: one was used to drive the solar panels to adjust to the slope of the surface (horizontal north-south axis) and the other was used to drive the solar panels to adjust to the azimuth angle of the surface (vertical axis). By using the two moving axes sun tracking system, the surface of the solar panels showed an increase in total capturing of solar energy as compared to single ï¬xed tilted surface. The experimental study showed that the increase in the collected energy increased by 41.34% (Abdallah & Nijmeh, 2004). In the same year, Reda and Andreas worked on a new procedure to implement a step-by-step solar position algorithm. The algorithm derived the solar zenith, azimuth and incidence angles based on parameters as ecliptic longitude and latitude for mean Equinox of date, apparent right ascension and apparent declination. The algorithm also included some correction parameters as nutation in longitude, nutation in obliquity, obliquity of ecliptic and true geometric distance (Reda & Andreas, 2008). In 2007, Chen and Feng developed a solar tracking system on the principle of analogue optical non linear compensation. The traditional analogue sensor consisted of a thin mask with a square aperture that was placed above a quadrant detector.
The square aperture consisted of four slits of equal width. A projective image is formed on the detector's plane by the illumination of incident sunlight in different positions of the detector, depending on the relative angle of the sensor axis. As a result, in a traditional analogue solar sensor the azimuth and elevation angles are obtained by the basic geometrical principles by processing the signals. The output signals vary non-linearly with the azimuth and elevation angles,i.e., sensor sensitivity depends on the incident angle of the sunlight. As a solution to this problem, the author's modiï¬ed the aperture area per unit length varied in accordance with speciï¬c laws. Thus, the nonlinear displacement of the projective image on the detector's plane caused by linear changes in the incident angle of the sunlight was compensated by the nonlinear aperture area per unit length such that the output of the sensor varied linearly with the input (Chen & Feng, 2007).
History of Microcontrollers
The Microcontroller was first developed in the early 1970's by a company called Intel (Integrated Electronics). Intel was a small company and its client refused to buy the product. So Intel decided to market its microprocessor as a general-purpose chipset, which was extensively used wherever digital logical chips were used. The success of this microprocessor triggered Intel to research more on microprocessors and very soon it developed a 4-bit microprocessor for general purpose. 4004 is much more advanced and it is designed and marketed as a "general purpose" chipset.
Later, Intel in association with TI produced an 8-bit central processing unit (CPU) with a 14-bit data memory bus, which can address up to 16KB of memory. The CTC (computer Terminal Corporation) ordered Intel and Texas Instruments to build them an 8-bit processor that can be used in terminals. Soon CTC gave up its idea. Even then Intel and TI kept working on the project and released a microprocessor 8008, which is able to address 16KB of memory and operation speed of 300 000 operations per second. Later an updated model of 8008, i.e. 8080 was very soon released which has operating range of +5V, -5V and +12V using NMOS technology.
Observing these developments in technology, Motorola released its first ever microprocessor, the 6800. Motorola was the only company to make other peripherals such as 6820 and 6850. 6800 is an 8-bit with almost the same specifications as of 8080. The architectures used in 8080 and 6800 differ a lot. The architecture used in Intel 8080 is a register based. The registers are from AX, BX, CX, DX, and HL. All are 16-bit but are capable of being used as an 8-bit register pairs. So the register AX can be used as two separate registers, i.e. AX can be used as AH and AL. Where AH a byte higher than AX, where as AL is is the previous lower byte. In the similar way each and every register BX, CX, DX, and HL can be used as BH, BL, CH, CL, DH, DL, H, and L.
Also Intel 8080 has separate I/O map. This is given separately to provide byte-wide input/output to hardware. Some special instructions are used to perform either input or output to the hardware. The instruction for accepting a byte-wide input from it's input port is IN. Similarly OUT is to output a byte-wide output to the output port. The MOV instruction is used to get access to memory from a different memory map.
Motorola 6800 used "Memory Mapped Input/Output". Memory mapped input/output is nothing but sharing of the same memory map by both memory and byte-wide input and output, which is different from Intel 8080. Also the register set consisted of two 8-bit accumulators, i.e. A and B, and an index register X. The index register X is of 16-bits and this makes the register set much smaller than Intel 8080. However small, these registers can support a range of addressing modes. These addressing modes are made up for few registers and simple programming. The data input from the memory or from input source requires the use of LDAA. This is used to write data to the memory or input/output requires the use of STAA instruction. The access to register X is was through an own set of instructions, i.e. LDX and STX.
As before both the companies Intel and Motorola have maintained differences in their development of further microcontrollers. The Intel upgraded it's 8080 to 8085, in 1977which is also 8-bit processor like 8080 and is first 5V CPU gave '5' in the place of '0'. Intel was very keen on upgrading microprocessors. Very soon 8086, 8088 and later 80186 were released. 800386 is a 32-bit processor and 80486 leading to the design of Pentium range of microprocessors which are 64-bit processors. 80x86 and Pentium range processors are specially designed for personal computer applications. They have large memory maps. Motorola's microprocessors followed similar path by replacing 6800 with 6809, an 8-bit and then by 68000, a 16-bit. The microprocessors 68010, 68020, 68030 were used in many workstations and also in personal computers like Apple MAC.
The most recent microprocessors in the present market use Harvard architecture and use of Reduced Instruction Set Computers (RISC) have led to the development of microcontrollers such as Microchip PIC.
Microcontroller 8051: Micro controller is at the heart of the system and following description gives an idea of this crucial component. The IC 8051 is a low-power; high-performance CMOS 8-bit microcomputer with 4K bytes of flash memory. The pin diagram of 8051 is shown in Figure 3. The device is manufactured by Atmel and is compatible with comparable industry pin out. There is advantage of flash memory because it is non-volatile. This allows a program to be stored even when we lose power. Atmel IC 8051 combines a 8-bit CPU with Flash memory on a single die chip. It also provides a highly-flexible and cost-effective solution to many embedded control applications. standard features that come with IC are: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timers and counters, a five vector dual level interrupt architecture, full duplex serial port and oscillator along with clock circuitry. In addition to all this features mentioned, ATMEL 8051 is designed with static logic for operation down to zero frequency and it supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the memory, timer counters, serial port and interrupt system to continue functioning.
FiFigure 3. Pin Diagram of 8051
Figure 4.Block Diagram of 8051
The block diagram explains internal circuitry of Microcontroller which is Shown in figure 4. These details are needed to understand and program microcontroller using embedded programming methods.
ULN 2003 7805:The ULN2001, ULN2002, ULN2003 and ULN2004 are high voltage, high current Darlington Arrays each one have seven open collector Darlington pairs with common emitters shown in below Figure 5. Each Channel rated at 500mA and can withstand peak currents of 600mA. Suppression diodes are included for inductive load driving and the inputs are pinned opposite the outputs to simplify board.
Figure 5. ULN 2003
There needs to be a driver placed, because the digital system and pins of microcontroller do not have enough current to drive the relay. The stepper motor's coil needs to be provided with 10mA of current in order to get energized, whereas the microcontroller pin provides a maximum of 2 mA current.
555 TIMER: The 555 monolithic timing circuit is a highly stable controller capable of produce accurate time delays, or oscillation. In the time delay mode of operation, the time is accurately controlled by external resistor and capacitor. For a stable operation as an oscillator, the free running frequency and the duty cycle are both accurately controlled with two external resistors and one capacitor. The pin diagram of a 555 TIMER is Figure 6. The circuit may be triggered and reset on falling waveforms, and the output structure can source or sink up to 200 mA.
Figure 6. 555 Timer
Stepper motor: There are several types of stepper motors; these cannot be driven in the same way. In this application note, we have chosen to drive a unipolar stepper motor for more information you will find schemes to identify the other types of stepper motors.
Figure 7. Stepper Motor
Unipolar Stepper Motor: Uni-polar stepper motors are characterized by their center-tapped windings.
Figure 8. Uni-polar Stepper Motor
Bipolar Stepper Motor : Bipolar stepper motors are designed with separate coils.
Figure 9. Bipolar Stepper Motor
Variable Reluctance: Variable reluctance stepper motor (also called hybrid motors) are characterized by one common lead.
Variable Reluctance Stepper Motor
Figure 10. Variable Reluctance Stepper Motor
Driving unipolar Stepper Motors: There are three ways to drive unipolar stepper motors (one phase on, two phase on or half step), each one has some advantages and disadvantages.
There are two stages to sorting out which wire is which in a 5 or 6-wire unipolar stepper motor:
In sorting out the wires as per their specifications for a 5 or 6 wire unipolar stepper method, a two step procedure is followed.
The resistance between the pairs of wires is checked with the help of ohmmeter by isolating the common power wire. The common power wire can be recognized by the resistance it offers, that it has only half of the resistance between it and all others. This is due to the reason that the common power wire carries only one coil, whereas other wires carry two coils between them. Thus only half of the resistance is observed in common power wire.
Next step is to identify the wires to the coils. Supplying a fixed amount of voltage on the common power wire, while keeping one of the other wires grounded does this. Each of the three remaining wires is grounded one by one in turn, and the results are observed. A wire is selected and grounded, thereby assumed as connected to coil 4. Each of other three wires is grounded in turn, and in the process the rotor turns clockwise for a particular grounded wire. It is assumed as connected to coil 3. Keeping these two wires as such, grounding one of the remaining wires will make the rotor turn anticlockwise, which is assumed as connected to coil 1. The wire, which makes the motor do nothing after grounding it is assumed as connected to coil 2.
Figure 11 . Center tapped winding
LDR(Light Dependent Resistor):The LDR is a component that changes its resistance with various levels of light. In the dark, the LDR presents a very high resistance like above 1 Mega Ohm. This resistance will fall below 100ohm under direct sun light. The LDR is a resistor, so that the current flow in the either direction. Although the LDR is very sensitive, seeing the levels of light that our eyes can't, the LDR is a slow device. Fast light changes can't be detected by an LDR. The upper limit of a frequency response of an LDR is around 10 KHz. If you need to detect faster light changes, you can use sensors such as photodiodes and photo transistors.
Using LDR is very easy, since it can directly bias semi conductor for devices such as transistors, SCRs, ICs etc., LDRs can be used as electronic eyes in applications involving robotics, mechatronics. As in human eye, a lens can be added to enhance the performance of an LDR in a particular application. By placing a convergent lens in front of an LDR, we can pick up more light from one direction, increasing sensitivity and adding directivity. LDRs can be found in different sizes and formats but, in general, their electrical characteristics do not differ much.
Figure 12: LDR& its Symbol
Summary of State of the Art
Most of the available literature describes open loop architectures for solar panel rotation. We have also reviewed the history and architecture of microcontroller development as microcontrollers are the heart of the electronic system used to control solar panel.
Chapter3
Method of investigation
Overview
This project seeks to explore a simple, cost effective and robust solution to adjust solar panels using sensors (photo transducer), 555timer, microcontroller and stepper motor. The idea behind this proposal consists of two photo transducers that collect light from two different positions on the solar panel and converts this light to analog voltage. A 555timer converts this voltage to digital format which can be fed to a microprocessor. The microprocessor can take inputs from two sensors and decide if we are collecting maximum light of if we need to change position.
There are two very clear advantages to this solution. One is: since this solution is closed loop i.e. take light input as a variable, adjustments are made till optimal point is reached. Also, we can program that adjustment to be made only 3 or 4 time a day not to cause failure of mechanical parts. Second advantage is that all the part of this system is off the shelf electronic components that bring down cost of implementation for mass production.
Description of Subjects and Equipment
To build the electronic systems as described we need several components that can be divided into three categories depending upon where they fit into the overall system. Block diagram is shown in Figure 13.
1) Light dependent Resistors (LDRs): These sensors capture light and need to be mounted on the top of solar panels to capture light. This project will have electrical wires with appropriate weather insulation, to connect LDRs to rest of electrical system. In the demonstration system that proves research concepts, the weather insulation is not given priority, but is emphasized as a requirement for volume production of prototype.
2) Electronic system: Electronic system consists of a printed circuit board (PCB) that connects various chips as described in the schematic diagram is shown in Figure 14. These connections are made with thin copper metal that is coated on the top of insulating board to keep various signals electrically isolated. Once the required connections are drawn, the PCB is coated with insulating material to prevent accidental short circuits in actual operation. Electronic chips like Microcontroller, 555 timer and ULN (buffer). Passive electronic components like resistors and capacitors to give correct currents and voltages to microchips. A transformer that takes AC power from mains and steps down to a lower voltage and bridge rectifier that converts this lower AC voltage into DC voltage 5V battery.
A housing (plastic box) is needed to keep all these components together in volume production. In a typical home solar system, this part of the system is kept indoors to shield from outside weather.
3) Stepper Motor: A motor is needed to turn the solar panel. This motor needs to build into the hinge that holds solar panel to a permanent structure.
Methodology
This project proposes to demonstrate the concepts of closed loop control of solar tracking system using off the shelf electronic components that can be ordered from electronic component houses like Mouser electronics or Dig key. The tasks that are involved in implementation are going through a list of suitable components that fit the system. For example there are various programmable micro controllers with different degrees of complexity of features. We should choose the microcontroller that performs the required arithmetic operation without adding complexity or cost that is not needed. A detailed description of each of the chosen components follows in the report. Once the chips are chosen, we need to look at voltage requirements of these chips and also any resistors or capacitors that need to add to the schematic diagram for these chips to function as specified in their datasheets.
Figure 13. Block Diagram of Solar Tracker
After the schematic diagram is finalized, we need to build a printed circuit board using software to build PCBs and have the PCB manufactures and all the chips soldered on. The complete system need to be built with required transformers and demonstrated to prove the concept.
Research Design and Procedures
The objective of this project is to control the position of a solar panel in accordance with the motion of sun and make sure that solar panel captures maximum amount of solar energy possible.
The angle at which sun rays fall on the surface of the solar panel determined the amount of energy captured by the solar panel. As described in statement of purpose this project explores the ways to auto adjust position of solar panel to capture maximum sunlight.
This project is designed with solar panels, LDR (Light dependent resistor) sensors, 555 Timer, microcontroller, stepper motor and its driving circuit. In this project two LDRs are fixed on the solar panel at two distinct points.
LDR varies the resistance depending upon the light fall. Since two sensors are located at two different places on the panel, we get two distinct resistances corresponding to the way panel is oriented. This resistance is converted into a voltage by giving a bias current to LDRs. The converted voltage is given as input to 555Timer.
Inside 555Timer the varied resistance is compared with a reference voltage and converted into a digital signal. Then the converted digital signal is given as the input of the microcontroller. Microcontroller receives the two digital signals from the sensor circuit and compares them. Unless the solar panel is in optimal position where this project gets maximum solar energy, the LDR signals are not equal. When there is a difference between LDR voltage levels, the microcontroller program drives the stepper motor towards optimal position or normal incidence of sunlight. This as a feedback system as explained above since this correction mechanism keeps happening until solar panels are in optimal position.
Description of Measures Employed
Implementation:
LDR: LDR is represented by U6 and U8 in the schematic diagrams. For electrical modeling purposes this is nothing but a resistor whose value is controlled by the light that falls on it. To sense the LDR resistance value, it is connected in series with 10K resistor thus forming an effective resistive divider. When light falls on the LDR, its resistance will be low and voltage at pin2 of 555timer will be close to supply voltage (VDD). When there is no light on LDR, the voltage at same pin 2 will be close to ground at 0V. Thus it can show the amount of light falling on LDR by looking at voltage on pin2 of 555timer.
555timer: This circuit is used to filter any noise coming out of LDR. Pin2 of 555timer has noisy voltage that depends on amount of light falling on LDR. This voltage can be digitalizing such that any voltage above two third of supply voltage will be an ON position and any voltage below one third of supply voltage will be an OFF position. 555 timer as connected in schematic shown in Figure18 will act as Schmitt trigger (A digitizing buffer with noise filtration built in). The resistor R1 and capacitor U9 determine the amount of noise filtration we are getting out of this circuit. Capacitance U5 helps to remove any noise from ground line of the power supply.
Microcontroller: All microcontrollers need a master clock frequency to run their operation. This clock frequency is generated using accurate quartz crystal. In Figure 19 X1 is the quartz crystal and U10, U11 represent the required capacitances that adjust the frequency of master clock. R5 is again a noise filtering resistor for this crystal oscillator. Capacitance C1 filters the power supply noise going into microcontroller. Given that microcontroller is the main part of the system, we have a dedicated noise filtering capacitor on its power supply line.
Buffer: ULN 2003 is just a buffer that takes digital signals of microprocessor and converts them into a format that can supply large amounts of currents needed by stepper motor. This circuit is not required from a logical diagram of the circuit, but, is inserted to take care of practical necessities of driving a stepper motor. Figure 14. Schematic Diagram of Solar tracker
Stepper Motor: Stepper motor is a simple DC motor that runs based on amount of voltage applied to its inputs and will be used to turn solar panels.
Signal Conditioning
In this proposal light dependent resistors are used to track the motion of Sun by sensing the Sun ray. Due to the light variations the output of the light dependent resistor changes accordingly. In order to control the drastic changes at output that is movement the solar panel due to variation of current at output of the light dependent resistor, 555 timer (Schmitt trigger) is used. Schmitt trigger is type of comparator, built by using 555 timer. It measures the input whether it is above or below the threshold. The threshold varies to make it less likely that the output will switch rapidly back and forth due to a noisy input near the threshold. This Schmitt trigger circuit is a inverting buffer (NOT gate), so the output is high when the input is low (below threshold1/3 of Vcc) and output is low when the input is high (above threshold 2/3 of Vcc).
In order to get these threshold voltages (signal conditioning) at the input of the 555 timer, a variable resistor is used in series with the LDR to form voltage divider. The dark resistor of LDR used in this project is around 1M ohm and it decreases 4K ohms when illuminated byr more light, so the series variable resistor is selected accordingly to 10K ohms. 120 K ohms resistor is connected in series with 0.01uf to filter the noise at input of 555 timer. The signals from the two sensors are compared by using the microcontroller programming and produces output to drive the stepper motor.
Figure 14 shows the connection of discussed components. As we can see all the components are chosen to use the same DC voltage of 5V that will be produced by the rectifier. Primary concerns in implementing the system are: All electronic components require a fixed and regulated power supply for them to function as specified. If the circuit has signaled that are connected to many components, project needs to evaluate the drive strength or the current that is supplied by the chip that outputs the signal. If microcontroller does not have sufficient drive strength output from micro controller, we need to use a chip called buffer integrated circuit to give sufficient current.
Choosing 555 timer:
Given that solar tracker system is a closed loop system, we get a lot of flexibility in terms of choosing components. If we choose an ADC that has less accuracy and if gives a result that is slightly different from the most accurate result, we can always correct this as we get feedback until the solar panel is in optimal position. Since this is a research project we can demonstrate that we can get away with very low accuracy converters by using a 1-bit ADC which is essentially a digital inverter. This idea is implemented using a 555 timer in a Schmidt trigger configuration. Schmitt trigger configuration is required to eliminate any noise from LDRs.
Choosing a buffer for microcontroller outputs:
As discussed above, microcontroller outputs might not have enough drive strength to provide require current to stepper motor. Digital systems and microcontroller pins lack sufficient current to drive the relay. While the stepper motor's coil needs around 10ma to be energized, the microcontroller's pin can provide a maximum of 1-2mA current. For this reason, we place a buffer driver between microcontroller and relays.
Choosing a stepper motor:
Uni-polar stepper motors with center tapped winding are ideally suited for our application since we have a single power supply that is needed to power both the stepper motor and rest of the electronics. Having a center tapped stepper motor lets us utilize the low voltage most effectively since we are effectively doubling the voltage in a center tapped transformer.
Power supply:
Theoretically we have two choices to power the electronic system. We could use the DC power supplied by the solar panel to power all the electronics and the stepper motor or we can get power from AC mains. Both cases need step down from a higher voltage to lower voltage.
We choose to get power from the mains for several reasons: It is easy to step down AC voltage using a transformer.AC power would be more reliable on a cloudy day. Most of the solar panels are connected to grid anyway. So, getting AC power for electronics does not put any extra requirements on the system.
