program-embedded micro-controller as a viable … · 3.1 interfacing the analog output with the adc...

Sept. 2013. Vol. 4, No.1 ISSN 2305-1493 International Journal of Scientific Knowledge Computing and Information Technology

© 2012-2013 IJSK & K.A.J. All rights reserved www.ijsk.org

1

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:[email protected], Mobile Phone:08034015858

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

E-mail:[email protected], 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



2

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).



3

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).

out

in

out

in

R

R

V

V

(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):



4

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):

TTOSCOSC

CRTF

2

18.118.1

(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)



5

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.

PIC1

6F87

3A

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

2108 111111112551212 n

inR

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).

210 11111110254,255

49.2

50.2 out

outout

in

out

in RRR

R

V

V

Similarly, the binary Resolution corresponding to the

lower threshold voltage (1.83V) is:

210 10111011187,255

83.1

50.2 out

outout

in

out

in RRR

R

V

V

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



6

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:

%7.63%1002.314

200%100 x

s

sx

T

TD

OSC

on

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):

MHzKHznS

fOSCTOSC 8.37.3755569

2.314

18.118.1

(Preferred value = 4MHz).

3.2 Software Programming of the

microcontroller The 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;******************************

***************************

;-----------PortA

SWITCH Equ PORTA

POWER_SW Equ 0x00;

TEST_SW Equ 0x01

SENSOR Equ PORTA

EASTSENS Equ 0x02

MIDSENS Equ 0x03

WESTSENS Equ 0x04

;-----------PortB

MOTOR_PORT Equ PORTB

;-----------PortC

LED_PORT PORTC

LED_POWER Equ 0x00;

LED_NORMODE Equ 0x01

LED_TESTMODE Equ 0x02

LED_EASTSENS Equ 0x03

LED_MIDSENS Equ 0x04

LED_WESTSENS Equ 0x05

LED_MOTORACT Equ 0x06

;**********************************

******************

cblock 0x20

;start of general purpose

registers

endc

cblock 0x70 ;start of

multi bank general purpose

registers

w_temp

status_temp

pclath_temp

endc

;**********************************

***************************



7

;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,RP0

BCF STATUS,RP1 ;Bank

0

CLRF PORTA ;Initialize

all PORTS by

CLRF PORTB ;clearing

output

CLRF PORTC ;data

latches

BSF STATUS,RP0 ;Bank 1

MOVLW 0x06 ;Configure all

pins

MOVWF ADCON1

MOVLW 0xFF ;Configure all

pins on port A

MOVWF TRISA ;as digital

inputs


pins on port B

MOVWF TRISB ;as digital

outputs


pins on port C

MOVWF TRISC ;as digital

outputs

;----------------------------------

------

;initialising ports

;----------------------------------

-----

BCF STATUS,RP0 ;Return to

Bank 0

;Initialise the stepper motor

BCF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CLRF LED_PORT

;----------------------------------

-----

;power switch scan start

;----------------------------------

-----

POWSW: BTFSS SWITCH, POWER_SW

GOTO POWON

GOTO POWSW

;----------------------------------



8

;system on and start switch scan

for test and normal operation

POWON: BSF LED_PORT, LED_POWER

;Put on led reo

CALL DELAY1S

CALL 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_NORMODE

CALL DELAY240S

BSF LED_PORT,LED_TESTMODE

CALL DELAY240S

BCF LED_PORT,LED_TESTMODE

CALL DELAY240S

BCF LED_PORT,LED_NORMODE

CALL DELAY240S

GOTO SWSCAN

;----------------------------------

------

;Normal operation begins here

;----------------------------------

-----

OPEPR:

BSF LED_PORT,LED_NORMODE

;

;Searching for active sensor

SENS_SCAN1:

BTFSC SENSOR,EASTSENS

GOTO STOP_SCAN1

BTFSC SENSOR,MIDSENS

GOTO STOP_SCAN1

BTFSC SENSOR,WESTSENS

GOTO STOP_SCAN1

;CALL MOVE_WWARD

GOTO SENS_SCAN1

;-------------

STOP_SCAN1:

BTFSS PORTB,6

GOTO SENS_SCAN2

CALL STEPFW

GOTO SENS_SCAN1

;----------------------------------

-------

SENS_SCAN2:


GOTO STOP_SCAN2


GOTO STOP_SCAN2


GOTO STOP_SCAN2

;CALL MOVE_EWARD

GOTO SENS_SCAN2

;-------------

STOP_SCAN2:

BTFSS PORTB,5

GOTO STOP_SCAN

CALL STEPBW

GOTO SENS_SCAN2

;---------------------------------

STOP_SCAN:


GOTO STOP_SCAN


GOTO STOP_SCAN


GOTO STOP_SCAN

GOTO STOP_SCAN1

;-------------------------

;

MOVE_WWARD:

BTFSS PORTB,6

GOTO NIGHT_TIME

CALL STEPFW

CALL DELAY4M

RETURN

NIGHT_TIME:

CALL DELAY90M

RETURN

;-------------------------

;

MOVE_EWARD:

BTFSS PORTB,5

RETURN

CALL STEPBW

CALL DELAY4M

RETURN

;----------------------------------

-----

;Testing subroutine start here

;----------------------------------

-----

TESTP:

;----------------------------------

--

;Initialize tray



9

BTFSS PORTB,5

GOTO INIT_OVER

CALL STEPBW

GOTO TESTP

INIT_OVER:


CALL DELAY1S


CALL DELAY1S


CALL DELAY1S


CALL DELAY1S


CALL DELAY240S

TRYSTP0:

MOVLW D'14'

MOVWF 0X040

BSF LED_PORT,LED_EASTSENS

BCF LED_PORT,LED_MIDSENS

BCF LED_PORT,LED_WESTSENS

CALL DELAY240S

CALL DELAY240S

BCF LED_PORT,LED_EASTSENS

CALL DELAY240S

CALL DELAY240S

BTFSS SENSOR,EASTSENS

;Sensor scanning for east

GOTO MOVSTEP0

GOTO TRYSTP0

TRYSTP1:

MOVLW D'14'

MOVWF 0X040


BSF LED_PORT,LED_MIDSENS


CALL DELAY240S

CALL DELAY240S


CALL DELAY240S

CALL DELAY240S

BTFSS SENSOR,MIDSENS

;Sensor scanning for midd

GOTO MOVSTEP1

GOTO TRYSTP1

TRYSTP2:

MOVLW D'14'

MOVWF 0X040



BSF LED_PORT,LED_WESTSENS

CALL DELAY240S

CALL DELAY240S


CALL DELAY240S

CALL DELAY240S

BTFSS SENSOR,WESTSENS

;Sensor scanning for west

GOTO MOVSTEP2

GOTO TRYSTP2

MOVSTEP0:

CALL STEPFW

DECFSZ 0X040,F

GOTO MOVSTEP0

GOTO TRYSTP1

MOVSTEP1:

CALL STEPFW

DECFSZ 0X040,F

GOTO MOVSTEP1

GOTO TRYSTP2

MOVSTEP2:

CALL STEPFW

DECFSZ 0X040,F

GOTO MOVSTEP2

GOTO MOVFED

MOVFED: NOP ;Forward

endding pertern


CALL DELAY1S


CALL DELAY1S


CALL DELAY1S


CALL DELAY1S

MOVLW D'42'

MOVWF 0X040

TRYBWD:

BSF LED_PORT,LED_EASTSENS

BSF LED_PORT,LED_MIDSENS

BSF LED_PORT,LED_WESTSENS

CALL DELAY240S

CALL DELAY240S




CALL DELAY240S



10

CALL DELAY240S

BTFSS SENSOR,EASTSENS

;Sensor scanning for east

GOTO MOVSTEPB

BTFSS SENSOR,MIDSENS

;Sensor scanning for midd

GOTO MOVSTEPB

BTFSS SENSOR,WESTSENS

;Sensor scanning for west

GOTO MOVSTEPB

GOTO TRYBWD

MOVSTEPB: NOP

CALL STEPBW

DECFSZ 0X040,F

GOTO MOVSTEPB

CALL DELAY1S

;Ending testing routines


CALL DELAY1S


CALL DELAY1S


CALL DELAY1S


CALL DELAY240S

NOP





GOTO SWSCAN

;----------------------------------

------

;Stepping motor routine

;----------------------------------

------

STEPBW: BSF

LED_PORT,LED_MOTORACT

;MOVLW 0x10

;MOVWF MOTOR_PORT

BSF MOTOR_PORT,4

BCF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

CALL DELAY1S

;MOVLW 0x04

;MOVWF MOTOR_PORT

BSF MOTOR_PORT,2

BCF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,4

CALL DELAY1S

;MOVLW 0x02

;MOVWF MOTOR_PORT

BSF MOTOR_PORT,1

BCF MOTOR_PORT,0

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CALL DELAY1S

;MOVLW 0x01

;MOVWF MOTOR_PORT

BSF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CALL DELAY1S

BCF LED_PORT,LED_MOTORACT

RETURN

;-------------

STEPFW: BSF

LED_PORT,LED_MOTORACT

BSF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CALL DELAY1S

BSF MOTOR_PORT,1

BCF MOTOR_PORT,0

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CALL DELAY1S

BSF MOTOR_PORT,2

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

BCF MOTOR_PORT,4

CALL DELAY1S

BSF MOTOR_PORT,4

BCF MOTOR_PORT,0

BCF MOTOR_PORT,1

BCF MOTOR_PORT,2

CALL DELAY1S

BCF LED_PORT,LED_MOTORACT

RETURN

;----------------------------------

-----

;TIMER ROUTINES

;----------------------------------

-----

DELAY1MS:



11

MOVLW 0XFA ;1 sec delay,

d'240'

MOVWF 0X060

LOOP1: NOP

DECFSZ 0X060,F

GOTO LOOP1

RETURN

DELAY240S: ;240 sec delay

MOVLW 0XFA ;d'240'

MOVWF 0X061

LOOP2: CALL DELAY1MS

DECFSZ 0X061,F

GOTO LOOP2

RETURN

DELAY1S: ;1 sec delay

MOVLW 0X4 ; d'4'

MOVWF 0X062

LOOP3: CALL DELAY240S

DECFSZ 0X062,F

GOTO LOOP3

RETURN

DELAY1M: ;1 min delay

MOVLW 0XF0 ;d'240'

MOVWF 0X063

LOOP4: CALL DELAY240S

DECFSZ 0X063,F

GOTO LOOP4

RETURN

DELAY4M:

MOVLW 0X04

MOVWF 0X064

LOOP5: CALL DELAY1M

DECFSZ 0X064,F

GOTO LOOP5

RETURN

DELAY90M:

MOVLW 0X5A

MOVWF 0X065

LOOP6: CALL DELAY1M

DECFSZ 0X065,F

GOTO LOOP6

RETURN

;-----------------------------

;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

Output

Output

Output

Output

1 0 0

0 1 0

0 0 1

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



12

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 Application

MCLR 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



13

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www.Microchip.com

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Microelectronics Circuits. Volume 1 Oxford

University Press: New York.

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