PROGRAM-EMBEDDED MICRO-CONTROLLER AS A VIABLE DEVICE IN

AUTOMATIC SOLAR ENERGY TRACKING TECHNIQUE

*Gesa, F.N , **Awoji M.O and ***Ilouno Joseph

*Department of Physics, University of Agriculture Makurdi, P.M.B 2373 Makurdi, Benue State.

Email:gesnewx@yahoo.co.uk, Mobile Phone:08034015858

**Department of Physics, Kwararafa University Wukari, P.M.B 1019 Taraba State.

E-mail:michaelawoji@gmail.com, Mobile Phone:08067761427

***Department of Physics, University of Jos, P.M.B 2084 Jos, Plateau State-Nigeria.

ABSTRACT

This research employs a hardware-software-embedded program Control System to optimize solar

energy collection in solar payloads. The basic hardwares comprised a programmable

Microcontroller (PIC16F873A) coupled to three Cadmium-Sulphide (CdS NORP12-RS)

resistors via an LM324 comparator. The software used in the design is MPLAB IDE Compiler

8.10. The PIC16F873A was programmed in machine language using the MPLAB IDE compiler

interface for Microchip PIC devices. This enables the PIC16F873A receives and compares solar

intensities sensed by the CdS NORP12-RS then relays binary-coded tracking instructions to a

stepper motor circuit. The microcontroller was tested to have switched ‘ON’ or ‘OFF’ in pair a

bi-quad transistor network connected to a half-stepped motor of torque 61.2Nm which tracks a

payload in the direction favourable to maximum solar intensity as compiled in the program.

Preamble

In the recent times, solar energy supply has taken an integral position in the struggle for

effective energy acquisition. This is necessitated by the global search for environment-friendly

energy sources that cause less harm to man’s natural habitat. In fact, the drastic depletion of

ozone layer to the fossil fuels which leads to global warming, ionospheric degradation among

other things has been the spring board for alternative energy search. Though the photovoltaic

energy production from the sun has been successfully achieved, it has not been devoid of

challenges and limitations. These limitations which include the sun movement, weather/climate

changes, difficulty in solar rays collection process etc. have in a way significantly limit the

output of solar devices to a minimal low efficiency of about 19% (Manikatla, 2005).Therefore an

urgent need to increase the efficiency of the solar energy collection process thereby increase the

output from solar devices arises. This if achieved, would make such devices more viable in a

world full of energy crises.

Key words: Micro-controller in Solar Energy Tracking

1.0 Theory of Micro Controller

Before the advancement in microelectronics which introduced microcontrollers,

microprocessors were mostly used in various applications. It is a programmable device that takes

in numbers as input, performs arithmetic and logic operations on them according to programs

stored in memory and produces the result as output. It is programmable in the sense that it

performs a given set of operation based on the sequence of instructions given to it (Saxena and

Dutta 1990).

In such a device, data is taken in through the use of input devices like the mouse,

keyboard, switches etc. Since numbers are seen by the microprocessor only in binary digits, a

microprocessor needs the following items connected to make it a complete computing device

(Crisp, 2004).

i. Instruction set

ii. RAM

iii. ROM, PROM or EPROM

iv. Input/output ports

v. Clock generator

vi. Reset function

vii. Serial port

viii. Interrupts

ix. Timers

x. Analog-to-digital converters

xi. Digital-to-analog converters

Hence, a device that contains the microprocessor and all the above units in a single

package is called a microcontroller. Some commonly used microcontrollers are: PIC16F873A,

PIC16F874A, PIC16F876A, and PIC16F877A. These are collectively named PIC16F87XA

where the x stands for the tolerance number (Microchip, 2010).

Table 1 Basic Features of PIC16F87XA Micro Controller Family (Microchip, 2010)

Key Features PICF873A

Operating Frequency 0-20MHz

RESETS (and Delays) POR,BOR (PWRT, OST)

FLASH Program Memory (14-bits

words)

4k

Data Memory (bytes) 192

EEPROM Data Memory (bytes) 128

Interrupts 14

Input/output ports Ports A,B,C

Timers 3

Capture /Compare/PWM modules 2

Serial Communication MSSP,USART

Parallel Communication -

10-bit Analog-to-Digital Module 5input Channels

Analog Comparators 2

Instruction Set 35

Packages 28-pin PDIP

28-pin SOIC

28-pin SSOP

28-pin MLF

1.1 Memory Organization of a Micro controller

There are two memory blocks in each of the PIC16F87XA devices. The Program

Memory and Data Memory have separate buses so that concurrent access to the memories can

occur (Saxena and Dutta 1990). The PIC16F87XA devices have a 13-bit program counter

capable of addressing an 8K word x 14 bit program memory space. The PIC16F876A/877A

devices have 8K words x 14 bits of FLASH program memory, while PIC16F873A/874A devices

have 4K words x 14 bits. To access a location in the memory, the physically implemented

address will cause a wraparound. The RESET vector at 0000h and the interrupt vector at 0004h

therefore restore the addresses after usage making the controller re-programmable if the need

arises (Crisp, 2004).

Fig. 2 Memory Organization of a Micro Controller (Crisp, 2004)

1.2 Resolution of a Micro controller

The resolution of a micro-controller can be obtained using the design equation from

Kularatna (2000).

R = 2n – 1 (1)

where n is the number of bit.

The high and low thresholds of the output signal from a micro-controller can be obtained using

the gain equation provided by Steyaert et al (2009).

V in

V out=

Rin

Rout (2)

where Vin is the input signal of the microcontroller, Vout is the threshold output signal, Rin is the

binary resolution corresponding to the input signal, Rout is the binary resolution corresponding to

the threshold output signal.

1.3 Pulse-Width-Modulation (PWM) and switching frequency of Microcontroller

The Pulse-Width-Modulation (PWM) in microcontroller is used to control duty cycle of a

motor drive. Power is supplied to the motor in square wave of constant voltage but varying

pulse-width or duty cycle. The duty cycle, D gives the amount of time the power switch is on, ton

in relation to the switching period, Tosc is expressed by (McLyman, 2004):

D = ton/TOSC x 100% (3)

Alternatively, the duty cycle, D is defined as (Malvino and Bates, 2007):

D = W/TOSC (4)

where, ton is the switch-on time, W is the width of pulses and TOSC is the switching period. This

Period of oscillation, TOSC of Pulse width modulation is expressed by (Microchip, 2010):

TOSC = 2πRTCT (5)

where, RT is the timing Resistor and CT is the timing Capacitor.

The switching frequency on the other hand is known as oscillation frequency. Switching is

usually at a constant frequency. Although some IC,s use a variable frequency with changing line

and load, With the microcontroller Integrated Circuits (ICs), it is possible to set the switching

frequency ‘FOSC’ with an external capacitor. The microcontroller IC operates at a frequency

which is programmed by one timing Resistor, RT and one timing Capacitor, CT.

The oscillator frequency, ‘FOSC’ is expressed by the approximate formula (Microchip, 2010):

FOSC=1 .18T OSC

= 1.182 πRT CT (6)

Practical values of RT fall between 3kΩ and 100kΩ, while those of CT fall between 10pF and

0.1μF. These values when selected results in oscillating frequency range of 2MHz to 50MHz

(Microchip, 2010).

2.0 Materials

PIC16F873A Microcontroller coupled to three Cadmium-Sulphide (CdS NORP12-RS) resistors

via an LM324 comparator, MPLAB IDE Compiler 8.10 for Microchip PIC devices, bi-quad

transistor network and a half-stepped motor.

3.0 Methodology

i. Interfacing the Analog output with the ADC of the microcontroller.

ii. Programming the microcontroller to compare stored digital equivalents of the threshold

values, against real time digital values obtained from varying sensor Analog voltage

outputs corresponding to various sensor positions.

Table 2 Specification and Designed parameters of the Microcontroller Circuit

Item Description

Microcontroller number PIC16F873A

Bit number 8-bit Multi channel ADC Converter

Current rating 25Ma

Supply Voltage 5V dc

Frequency 4MHz

Power rating <1 watt

Number of I/O ports 3

EEPROM Data Memory 128 x 4 K bytes

3.1 Interfacing the Analog output with the ADC of the microcontroller.

The Microcontroller represents the heart of the project as it controls the solar tracking procedure.

The microcontroller chosen for this project is capable of converting the analog photocell voltage

into digital values and also provides three output channels to control the motor rotation. The

PIC16F873A manufactured by Microchip is selected based on several reasons: it is

programmable, cheap, and consumes very little power and space. Below are the characteristics of

the chip.

i. Its size is small and equipped with sufficient output ports without having to use a

decoder or multiplexer. (Microchip datasheet, 2010)

ii. It has low voltage consumption. (Microchip datasheet, 2010)

iii. It has PWM inside the chip itself which allow us to vary the duty cycle of step-motor

drive (Microchip datasheet, 2010).

iv. Though complex in fabrication, it is simple to program since users would only need to

learn 35 single word instructions in order to program the chip (Crisp, 2004).

v. It can be programmed and reprogrammed easily (up to 10,000,000 cycles) (Crisp,

2004).

Pin configuration of PIC16F873A

Figure 4 shows the pin configuration of PIC16F873A in step Motor speed control system. Pins

not stated in appendix A1 are not used hence left floating.

Fig 4 PIC16F873A Micro controller Chip showing the Pin-in and Pin-out Configurations

When biased with the adequate supply voltage, the microcontroller would receive desired speed

from PC through serial port. The detected motor speed light sensor would then feedback to

microcontroller through RA0 of PIC16F873A. The microcontroller would operate as

programmed to produce a new duty cycle (from CCP2) that is proportional to the speed. Thus,

average voltage supply from DC motor drive can be varied in order to maintain the speed at the

desired value.

Calculations for Threshold Values of PIC16F873A

With reference to equations (1) and (2), the followings were obtained:

For an 8 bit Micro controller (ADC) used here,

i. Resolutions

Rin=2n−1=28−1=25510=111111112 ii. Threshold voltages

From the resolution above, a 2.50V analog input would correspond to

Therefore the binary resolution corresponding to the higher threshold voltage (2.49V) is

determined using equation (3).

V in

V out=

Rin

Rout=2 . 50

2 . 49=255

Rout, Rout≈25410=111111102

Similarly, the binary Resolution corresponding to the lower threshold voltage (1.83V) is:

V in

V out=

Rin

Rout=2 .50

1 .83=255

Rout, Rout≈18710=101110112

The program written in the MPLAB therefore uses these threshold values as tracking voltage

reference values of the LDR (See Program).

Calculation of the PWM and Switching Frequency of PIC16F873A

The Microcontroller used has a PWM switching Period TOSC given by equation (5) as:

TOSC = RTCT

With RT =5kΩ, CT = 10pF and Ton = 200ns (See Data sheet in appendix A1)

TOSC = 2πRTCT

TOSC = 2x3.142x5000 x (10x10-12)

TOSC = 3.142 x10-7 = 314.2 nS

The duty cycle from equation (3) is therefore:

D=T on

T OSCx100 %=200 ηs

314 .2 ηsx 100 %=63 . 7 %

This value is found good enough for the switching in synchronous signal systems like the solar

tracking device in this work (Maniktala, 2005).

The switching frequency of the oscillator is therefore given by equation (6):

f OSC= 1 . 18T OSC

= 1 .18314 . 2nS

=3755569 .7 KHz=3 .8 MHz (Preferred value = 4MHz).

3.2 Software Programming of the microcontrollerThe Source program for PIC16F873A Microcontroller;*************************************************************; Filename:gesanewtonsolartracker.asm ; Date: 29.06.2013; 5:34:18 pm ; File Version: Pic Ide 8.10 ; Author: Microchip Mplab*; Company: Microchip Incorporation *; **************************************************************; Notes: ; 1.80 DEGREE PER STEP

* 0.90 DEGREE PER HALF STEP; 2.49 HIGHER REFERENCE VOLTAGE FOR CONTROLLER* 1.83 LOWER REFERENCE VOLTAGE FOR CONTROLLER; ;*************************************************************

list p=16f873a ; list directive to define processor #include <p16f873a.inc> ; processor specific variable definitions errorlevel -302 ; Turn off banking message __CONFIG _CP_OFF & _WDT_OFF & _BODEN_OFF & _PWRTE_ON & _HS_OSC & _WRT_OFF & _LVP_ON & _CPD_OFF;*****************************************************;Port defintion begins here;*********************************************************;-----------PortASWITCH Equ PORTAPOWER_SW Equ 0x00;TEST_SW Equ 0x01SENSOR Equ PORTAEASTSENS Equ 0x02MIDSENS Equ 0x03WESTSENS Equ 0x04;-----------PortBMOTOR_PORT Equ PORTB;-----------PortCLED_PORT PORTCLED_POWER Equ 0x00;LED_NORMODE Equ 0x01LED_TESTMODE Equ 0x02LED_EASTSENS Equ 0x03LED_MIDSENS Equ 0x04LED_WESTSENS Equ 0x05LED_MOTORACT Equ 0x06;****************************************************

cblock 0x20 ;start of general purpose registersendccblock 0x70 ;start of multi bank general purpose registersw_temp status_temppclath_tempendc

;*************************************************************;RESET_VECTOR

ORG 0x0000 ; processor reset vector

goto start ; go to beginning of program

;************************************************************;INT_VECTOR

ORG 0x0004 ; interrupt vector location

INTERRUPT movwf w_temp ; save off current W register contents movf STATUS,w ; move status register into W register movwf status_temp ; save off contents of STATUS register movf PCLATH,w ; move pclath register into w register

movwf pclath_temp ; save off contents of PCLATH register; isr code can go here or be located as a call subroutine elsewhere movf pclath_temp,w ; retrieve copy of PCLATH register movwf PCLATH ; restore pre-isr PCLATH register contents movf status_temp,w ; retrieve copy of STATUS register movwf STATUS ; restore pre-isr STATUS register contents swapf w_temp,f swapf w_temp,w ; restore pre-isr W register contents retfie ; return from interrupt

;*********************************************MAIN_PROG start;---------------------------------------;Port configuration begins;---------------------------------------

BCF STATUS,RP0BCF STATUS,RP1 ;Bank 0CLRF PORTA ;Initialize all PORTS byCLRF PORTB ;clearing outputCLRF PORTC ;data latches

BSF STATUS,RP0 ;Bank 1MOVLW 0x06 ;Configure all pinsMOVWF ADCON1MOVLW 0xFF ;Configure all pins on port AMOVWF TRISA ;as digital inputsMOVLW 0x68 ;Configure all pins on port BMOVWF TRISB ;as digital outputsMOVLW 0x00 ;Configure all pins on port CMOVWF TRISC ;as digital outputs

;----------------------------------------;initialising ports;---------------------------------------

BCF STATUS,RP0 ;Return to Bank 0;Initialise the stepper motor

BCF MOTOR_PORT,0BCF MOTOR_PORT,1BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CLRF LED_PORT;---------------------------------------;power switch scan start ;---------------------------------------POWSW: BTFSS SWITCH, POWER_SW

GOTO POWONGOTO POWSW

;----------------------------------;system on and start switch scan for test and normal operationPOWON: BSF LED_PORT, LED_POWER ;Put on led reo

CALL DELAY1SCALL DELAY1S

;------------------------------------SWSCAN: BTFSS SWITCH,TEST_SW ;switch scan for test GOTO TESTP

BTFSS SWITCH,POWER_SW ;switch scan for NOR OPERATION GOTO OPEPR

BSF LED_PORT,LED_NORMODECALL DELAY240SBSF LED_PORT,LED_TESTMODECALL DELAY240SBCF LED_PORT,LED_TESTMODECALL DELAY240SBCF LED_PORT,LED_NORMODECALL DELAY240S

GOTO SWSCAN;----------------------------------------;Normal operation begins here;---------------------------------------OPEPR: BSF LED_PORT,LED_NORMODE;;Searching for active sensorSENS_SCAN1:

BTFSC SENSOR,EASTSENSGOTO STOP_SCAN1BTFSC SENSOR,MIDSENSGOTO STOP_SCAN1BTFSC SENSOR,WESTSENSGOTO STOP_SCAN1;CALL MOVE_WWARDGOTO SENS_SCAN1

;-------------STOP_SCAN1:

BTFSS PORTB,6GOTO SENS_SCAN2CALL STEPFWGOTO SENS_SCAN1

;-----------------------------------------SENS_SCAN2:

BTFSC SENSOR,EASTSENSGOTO STOP_SCAN2BTFSC SENSOR,MIDSENSGOTO STOP_SCAN2BTFSC SENSOR,WESTSENSGOTO STOP_SCAN2;CALL MOVE_EWARDGOTO SENS_SCAN2

;-------------STOP_SCAN2:

BTFSS PORTB,5GOTO STOP_SCANCALL STEPBWGOTO SENS_SCAN2

;---------------------------------STOP_SCAN:

BTFSC SENSOR,EASTSENSGOTO STOP_SCAN BTFSC SENSOR,MIDSENSGOTO STOP_SCAN BTFSC SENSOR,WESTSENSGOTO STOP_SCAN

GOTO STOP_SCAN1;-------------------------;MOVE_WWARD:

BTFSS PORTB,6GOTO NIGHT_TIMECALL STEPFWCALL DELAY4MRETURN

NIGHT_TIME:CALL DELAY90MRETURN

;-------------------------;MOVE_EWARD:

BTFSS PORTB,5RETURN CALL STEPBWCALL DELAY4MRETURN

;---------------------------------------;Testing subroutine start here;---------------------------------------TESTP:;------------------------------------;Initialize tray

BTFSS PORTB,5GOTO INIT_OVERCALL STEPBWGOTO TESTP

INIT_OVER:BSF LED_PORT,LED_TESTMODECALL DELAY1SBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODECALL DELAY1SBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODECALL DELAY240S

TRYSTP0:MOVLW D'14'MOVWF 0X040BSF LED_PORT,LED_EASTSENSBCF LED_PORT,LED_MIDSENSBCF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBCF LED_PORT,LED_EASTSENSCALL DELAY240SCALL DELAY240SBTFSS SENSOR,EASTSENS ;Sensor scanning for east GOTO MOVSTEP0GOTO TRYSTP0

TRYSTP1:MOVLW D'14'

MOVWF 0X040BCF LED_PORT,LED_EASTSENSBSF LED_PORT,LED_MIDSENSBCF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBCF LED_PORT,LED_MIDSENSCALL DELAY240SCALL DELAY240SBTFSS SENSOR,MIDSENS ;Sensor scanning for middGOTO MOVSTEP1GOTO TRYSTP1

TRYSTP2: MOVLW D'14'MOVWF 0X040BCF LED_PORT,LED_EASTSENSBCF LED_PORT,LED_MIDSENSBSF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBCF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBTFSS SENSOR,WESTSENS ;Sensor scanning for westGOTO MOVSTEP2GOTO TRYSTP2

MOVSTEP0: CALL STEPFWDECFSZ 0X040,FGOTO MOVSTEP0GOTO TRYSTP1

MOVSTEP1:CALL STEPFWDECFSZ 0X040,FGOTO MOVSTEP1GOTO TRYSTP2

MOVSTEP2:CALL STEPFWDECFSZ 0X040,FGOTO MOVSTEP2GOTO MOVFED

MOVFED: NOP ;Forward endding perternBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODECALL DELAY1SBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODE

CALL DELAY1SMOVLW D'42'

MOVWF 0X040TRYBWD:

BSF LED_PORT,LED_EASTSENSBSF LED_PORT,LED_MIDSENSBSF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBCF LED_PORT,LED_EASTSENSBCF LED_PORT,LED_MIDSENSBCF LED_PORT,LED_WESTSENSCALL DELAY240SCALL DELAY240SBTFSS SENSOR,EASTSENS ;Sensor scanning for east GOTO MOVSTEPBBTFSS SENSOR,MIDSENS ;Sensor scanning for middGOTO MOVSTEPBBTFSS SENSOR,WESTSENS ;Sensor scanning for westGOTO MOVSTEPBGOTO TRYBWD

MOVSTEPB: NOPCALL STEPBWDECFSZ 0X040,FGOTO MOVSTEPBCALL DELAY1S

;Ending testing routinesBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODECALL DELAY1SBCF LED_PORT,LED_TESTMODECALL DELAY1SBSF LED_PORT,LED_TESTMODECALL DELAY240SNOPBCF LED_PORT,LED_EASTSENSBCF LED_PORT,LED_MIDSENSBCF LED_PORT,LED_WESTSENSBCF LED_PORT,LED_TESTMODE

GOTO SWSCAN;----------------------------------------;Stepping motor routine;----------------------------------------STEPBW: BSF LED_PORT,LED_MOTORACT

;MOVLW 0x10 ;MOVWF MOTOR_PORT

BSF MOTOR_PORT,4BCF MOTOR_PORT,0BCF MOTOR_PORT,1BCF MOTOR_PORT,2

CALL DELAY1S;MOVLW 0x04

;MOVWF MOTOR_PORTBSF MOTOR_PORT,2BCF MOTOR_PORT,0

BCF MOTOR_PORT,1BCF MOTOR_PORT,4

CALL DELAY1S;MOVLW 0x02

;MOVWF MOTOR_PORTBSF MOTOR_PORT,1BCF MOTOR_PORT,0BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CALL DELAY1S;MOVLW 0x01

;MOVWF MOTOR_PORTBSF MOTOR_PORT,0BCF MOTOR_PORT,1BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CALL DELAY1SBCF LED_PORT,LED_MOTORACTRETURN

;-------------STEPFW: BSF LED_PORT,LED_MOTORACT

BSF MOTOR_PORT,0BCF MOTOR_PORT,1BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CALL DELAY1SBSF MOTOR_PORT,1BCF MOTOR_PORT,0BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CALL DELAY1SBSF MOTOR_PORT,2BCF MOTOR_PORT,1BCF MOTOR_PORT,2BCF MOTOR_PORT,4

CALL DELAY1SBSF MOTOR_PORT,4BCF MOTOR_PORT,0BCF MOTOR_PORT,1BCF MOTOR_PORT,2

CALL DELAY1SBCF LED_PORT,LED_MOTORACTRETURN

;---------------------------------------;TIMER ROUTINES;---------------------------------------DELAY1MS:

MOVLW 0XFA ;1 sec delay, d'240'MOVWF 0X060

LOOP1: NOPDECFSZ 0X060,FGOTO LOOP1RETURN

DELAY240S: ;240 sec delayMOVLW 0XFA ;d'240'MOVWF 0X061

LOOP2: CALL DELAY1MS

DECFSZ 0X061,FGOTO LOOP2RETURN

DELAY1S: ;1 sec delayMOVLW 0X4 ; d'4'MOVWF 0X062

LOOP3: CALL DELAY240SDECFSZ 0X062,FGOTO LOOP3RETURN

DELAY1M: ;1 min delayMOVLW 0XF0 ;d'240'MOVWF 0X063

LOOP4: CALL DELAY240SDECFSZ 0X063,FGOTO LOOP4RETURN

DELAY4M: MOVLW 0X04MOVWF 0X064

LOOP5: CALL DELAY1MDECFSZ 0X064,FGOTO LOOP5RETURN

DELAY90M:MOVLW 0X5AMOVWF 0X065

LOOP6: CALL DELAY1MDECFSZ 0X065,FGOTO LOOP6RETURN

;-----------------------------;End of processing;-----------------------------

END ; directive 'end of program'

4.0 RESULTS

Measurement of Microcontroller digital outputs was taken every four minutes using

analogue-to-digital Multi-meter. The result is presented Table 3 complied with the switching

period specified in the algorithm of the embedded program.

Table 3 Compared Digital Input/output of the Controller

Comparator/CCP

Input East Sensor 1 Middle Sensor 2 West Sensor 3

Outpu

t

Outpu

1 0 0

0 1 0

0 0 1

t

Outpu

t

Outpu

t

0 0 0

5.0 Discussion

Table 3 shows the Microcontroller’s input and output digital signals for the three

comparators coupled to the East, Middle and West sensors respectively. The value of ‘1’

means ‘ON’ while ‘0’ means ‘OFF’. The null output (0, 0, 0) in Table 3 denote the reset

point at dark hour or zero luminance intensity when the resistance of each sensor

becomes large and the sensors do not conduct. However, an output like (0, 1, 0) implies

that the resistance of the middle sensor is least (its voltage output is highest) compare to

the east and west directional sensors. Therefore when this compared signal value is

coupled to the desired input transistors of the step motor, it tracks the payload to the

central position since that corresponds to the position of maximum photo intensity.

APPENDIX A1: Pin Configuration of PIC16F873A

Pin Name Pin No. Description ApplicationMCLR 1 Reset Input Clears the Memory when in

sleep mode

VDD 20 Positive Supply (+5V) Power Supply to Chip

Vss 8,19 Ground Reference Ground Reference

OSC1 9 For Oscillator Connected to oscillator 4MHz with 10pF

OSC2 10 For oscillator oscillator 4MHz with 10pF

RA0 2 Input/Output Pin Input of Vout from LM324 as speed counter

RB3 24 Input/Output Pin Output to control CW/CCW

of the motor

RB4 25 Input/Output Pin Output to control CW/CCW of the motor

RB1 22 Control pin control the phases of the stepper motor

CCP2 4 Capture/Compare/PMW Output of Duty Cycle to control motor speed

APPENDIX A2: Photograph of the implemented PIC16F873A Microcontroller IC

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