air conditioning control system using pic and stepper motors
DESCRIPTION
Embedded systemsTRANSCRIPT
1
AIR CONDITIONING CONTROL SYSTEM
MICROPROCESSOR ASSIGNMENT LECTURER: MR. SATHISH KUMAR
STUDENT NAME: MOHAMAD MUDDASSIR GHOORUN
1/13/2012
STUDENT NUMBER: TP018073
INTAKE CODE: UC4F1110EEE
2
TABLE OF CONTENTS:
1. INTRODUCTION AND OBJECTIVES
2. BLOCK DIAGRAM OF PROPOSED SYSTEM
2.1 EXPLANATION OF PROPOSED SYSTEM
3. INNOVATION TO ENHANCE THE SYSTEM
4. SIMULATION OF EACH BLOCK OF THE SYSTEM
UNIPOLAR STEPPER MOTOR CONCEPT
HALF STEPPING TECHNIQUE
5. FLOWCHART
6. EMBEDDED C PROGRAMMING
7. HARDWARE IMPLEMENTATION AND RESULTS
8. DISCUSSION
9. CONCLUSION
10. REFERENCES
3
1. INTRODUCTION AND OBJECTIVES:
The electric expansion valve (EEV) in an air conditioning system is what regulates the inflow
of refrigerant to the evaporator thereby affecting the temperature of the environment as shown in
the figure below. The objective here is to design and construct a prototype for an air conditioning
control system for 8 floors to regulate the air flow on each floor (1)
using a low cost
microprocessor or a microcontroller. A knob (5)
will then be used to regulate the amount of air
flow speed in 8 steps (2)
(0-7) for each floor. Step 0 is fully closed mode where no refrigerant
flows into evaporator while step 7 is fully open mode. The temperature of the surrounding (3)
is
also to be taken in consideration and kept constant. Furthermore, there should be two modes to
the operation (4)
of the system which comprises of both “summer mode” and “winter mode”.
4
2.1 BLOCK DIAGRAM OF PROPOSED SYSTEM:
PIC16F877A
TEMPERATURE
SENSOR
STEPPER MOTOR
DC MOTOR
KEYPAD
HEATER
BUZZER
5
2.1 EXPLANATION OF PROPOSED SYSTEM:
Temperature sensor LM35 (3)
is a precision integrated-circuit centigrade temperature
sensor whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. It
will thus be used to sense the temperature changes of the environment. A buzzer is included in
the design to indicate unusual temperature range, a dc motor used to force the refrigerant into the
evaporator of the air conditioner while a unipolar stepper motor controls the valve (1,2)
opening by
regulating the step angle (0 -7). Since we have two modes, that is the “summer mode” and the
“winter mode”, the block diagram includes a heater to be switched on during “winter mode” (4)
while during “summer mode”, only the DC motor will be on. Moreover, all the data including
the floor number is made available on the LCD and the valve may be regulated from the keypad
(5) itself (0-7), while the LCD also displays the temperature of the LM35 sensor.
LCD
6
3.0 INNOVATIONS TO ENHANCE THE SYSTEM’S OPERATION:
An LCD screen is made to interface the PIC16F877A so as to assist the personnel using the
system. The proposed system first asks whether the person wants “summer mode” or “winter
mode”. The floor number is displayed, followed by temperature sensor readings, and finally the
step control of valve. Moreover, a buzzer is also included in the design so as to indicate unusual
temperature i.e. greater than 29 degrees Celsius. Furthermore, the keypad is used to choose
“summer” or “winter mode”, the floor number and the valve control between 0 to 7. Simulation
of the enhancement can be shown below:
At temperature of 29 Degrees Celsius, we can see that the buzzer connected at RD7 is
off. Now, if temperature is further increased i.e. 30 degrees Celsius, the buzzer is to be
on as shown below:
7
4.0 SIMULATION OF EACH BLOCK OF THE SYSTEM:
Part 1:
As explained earlier, the system asks us which mode of operation we need. Buttons „*‟ and „#‟
on the keypad are used to choose the required mode selection.
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Part 2:
After choosing the “summer mode” or “winter mode”, the system asks us to choose the floor
number. It should also be noted that the DC motor and LED usage at port B are the outputs used
to differentiate between the 2 modes. When “summer mode” is chosen, only DC motor is on and
if “winter mode” is chosen, both the DC motor and the heating element (usually an inductor;
simulated as LED in our design) are on.
9
PART 3:
As shown above, the selected floor number is being displayed on the row 1 of the LCD screen.
PART 4:
10
Next is the step control option where we can choose between 0 to 7 which will control the step
angle of the motor. Also to note the buzzer right next to the keypad due to temperature being less
than 30 degrees Celsius. Furthermore, the relative temperature of the environment from the
LM35 sensor is also made available on the second line of the LCD.
PART5:
11
12
13
14
The above displayed the concept of the knob control whereby the stepper motor‟s angle of
rotation is controlled by using the keypad. See the pressed key and rotation angle for clearer
view. Also the concept of the unipolar stepper motor and connection is explained on the next
page.
15
PART 5B: UNIPOLAR STEPPER MOTOR CONCEPT
The below unipolar stepper motor has 90orotation step. The coils are activated in a cyclic order,
one by one. The proper angular movement of the rotor is determined by giving a „1‟ to the
specific coil as shown below. The coils are energized by giving a „1‟ to the pin to which they are
connected from the PIC. Thus, a proper sequence of the motor is achieved. However, this
unipolar motor moves only 4 steps that is 0 – 90 -180 -270 – 0. In order to achieve our 8 step
regulated valve concept, the half stepping technique will be used as shown on the next page.
16
PART5C: HALF STEPPING TECHNIQUE:
In the previous examples, only one coil has been activated at a time which hence made the rotor
move at an angle of 90 degrees. However, if two successive coils were to be energized equally at
the same time, the rotor will move half way the two coils, i.e. 45degrees. Thus, we can conclude
that half stepping technique can be used for doubling the amount of steps of a unipolar stepper
motor. This is a very important concept as it can increase efficiency of systems such as solar
trackers or other projects like robotic arms amongst others.
Thus referring back to the assignment the discussed technique has been used to regulate the
control valve from 0 to 7 with the help of the table below:
ROTATION ANGLE(DEG) RB PINS ON (1) RB PINS OFF (0) STEP
45 4 5,6,7 1
90 4, 5 6, 7 2
135 5 4,6,7 3
180 5, 6 4,7 4
225 6 4,5,7 5
270 6, 7 4,5,6 6
315 7 4,5,6 7
360/0 7, 4 5, 6 0
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5.0 FLOWCHART:
Initialize PIC and LCD
Display “summer mode” on line 1 and “winter mode” on line 2
If „*‟ chosen, DC motor on,
inductor off
If „#‟ chosen, DC motor on,
inductor on
Clear screen of lcd
“WELCOME” displayed line1
“Choose floor no” on line 2
Clear screen
Display “air conditioned” on line 1
Erase line 1
Display “floor number =” on line 1
Display “rel. temp=” on line 2
READ KEYPAD AND DISPLAY
FLOOR NUMBER ON LINE 1
AFTER “=” SIGN
READ TEMP. AND DISPLAY
TEMPERATURE ON LINE 2
AFTER “=” SIGN
B
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B
Clear line 1 and display „step control =‟ for the stepper motor
Display step (0-7) as pressed on the keypad after “step control
=”
Call stepper function to move unipolar stepper motor to
specific angle as shown in the half stepping technique in 5C.
Continue to monitor the keypad to change step angle whenever
another key is pressed (0-7) and call repeat last step
If no key is pressed, display “-” after “step-control =”
If temp>=30 degrees, activate the buzzer
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6.0 EMBEDDED C PROGRAM:
//header file
#include<pic.h>
//==========================================================
================
//pic configuration
__CONFIG (0x3F32);
//defining ports
#define lcd PORTC
#define RS RA2
#define E RA5
#define CHANNEL1 0b10001001 // AN1
//#define buzzer RB5 //buzzer at pin RB5
#define fan RB0
//#define fanB RB3
//#define ledA RB2
#define heater RB1
//#define pushbutton RE2
#define col_1 RD0
#define col_2 RD1
#define col_3 RD2
#define row_1 RD3
#define row_2 RD4
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#define row_3 RD5
#define row_4 RD6
//==========================================================
================
//function prototypes
void e_pulse(void);
void delay(unsigned short i);
void send_char(unsigned char data);
void send_config(unsigned char data);
void lcd_goto(unsigned char data);
void lcd_clr(void);
void dis_num(unsigned long data);
void increment(unsigned long data);
void read_adc(void);
unsigned short read_temp(void);
char keypad_read2 ();
unsigned short result;
unsigned short temp;
void first(); //just to break the program
//==========================================================
====================
void main(void)
{first();
}
//==========================================================
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//big function being invoked
void first()
{
ADRESH=0; //clear A/D result
ADRESL=0; //clear A/D result
//setting ADCON1 Register
ADCON1=0b11000101; // A/D result right justified, // configure RA2
//and RA5 as digital I/O
TRISA=0b11011011; //configure PORTA I/O direction
TRISB=0b00000000; //configure PORTB as output--------we'll
//configure this one only for the implementation of our inductor for heating and the
//fan for cooling concept here &stepper motor
TRISC=0b00000000; //configure PORTC as output
TRISD=0b00000111;
PORTA=0;
PORTD=0;
PORTB=0;
while(1)
{
send_config(0b00000001); //clear display at
lcd
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send_config(0b00000010); //Lcd Return to home
send_config(0b00000110); //entry mode-cursor increase 1
send_config(0b00001100); //diplay on, cursor off and cursor blink off//
send_config(0b00111100); //function set 5*10 dot matrix
//==========================================================
lcd_goto(0);
send_char('*');
send_char(':');
send_char(' ');
send_char('S');
send_char('U');
send_char('M');
send_char('M');
send_char('E');
send_char('R');
send_char(' ');
send_char('M');
send_char('O');
send_char('D');
send_char('E');
lcd_goto (20);
send_char('#');
send_char (':');
send_char(' ');
send_char('W');
send_char('I');
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send_char('N');
send_char('T');
send_char('E');
send_char('R');
send_char('-');
send_char('M');
send_char('O');
send_char('D');
send_char('E');
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
lcd_clr();
//==========================================================
char z;
z= keypad_read2();
if (z == '*')
{
fan=1;
}
else if (z == '#')
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{
fan=heater=1;
}
//==========================================================
send_char('#');
send_char('#');
send_char('#');
send_char('#');
send_char('W');
send_char('E');
send_char('L');
send_char('C');
send_char('O');
send_char('M');
send_char('E');
send_char('#');
send_char('#');
send_char('#');
send_char('#');
lcd_goto(20);
send_char('C');
send_char('H');
send_char('O');
send_char('O');
send_char('S');
send_char('E');
send_char(' ');
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send_char('F');
send_char('L');
send_char('O');
send_char('O');
send_char('R');
send_char(' ');
send_char('N');
send_char('O');
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
delay(10000000000000);
lcd_clr();
//==========================================================
//==========================================================
//display character on LCD
lcd_goto(1);
send_char('A');
send_char('I');
send_char('R');
send_char('-');
send_char('C');
send_char('O');
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send_char('N');
send_char('D');
send_char('I');
send_char('T');
send_char('I');
send_char('O');
send_char('N');
send_char('E');
send_char('D');
delay(10000000000000);
delay(10000000000000);
//==========================================================
lcd_goto(1);
send_char('F');
send_char('L');
send_char('O');
send_char('O');
send_char('R');
send_char('-');
send_char('N');
send_char('U');
send_char('M');
send_char('B');
send_char('E');
send_char('R');
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send_char('=');
send_char(' ');
char c;
c = keypad_read2();
send_char( c );
lcd_goto(20); //cursor go to 2nd line of the LCD
//display character on LCD
send_char('R');
send_char('E');
send_char('L');
send_char('.');
send_char('T');
send_char('E');
send_char('M');
send_char('P');
send_char('=');
delay(10000000000000);delay(10000000000000);
delay(10000000000000);delay(10000000000000);
delay(10000000000000);delay(10000000000000);
while(1){
lcd_goto(1);
send_char ('S');
send_char ('T');
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send_char ('E');
send_char ('P');
send_char ('-');
send_char ('C');
send_char ('O');
send_char ('N');
send_char ('T');
send_char ('R');
send_char ('O');
send_char ('L');
delay(10000000000000);delay(10000000000000);
delay(10000000000000);delay(10000000000000);
delay(10000000000000);delay(10000000000000);
keypad_read2();
lcd_goto(15);
char u;
u= keypad_read2();
send_char(u); //This is stepper motor control bit config
if (u=='1')
{RB4=1;RB5=RB6=RB7=0;}
else if (u=='2')
{RB4=RB5=1;RB6=RB7=0;}
else if (u=='3')
{RB5=1; RB4=RB6=RB7=0;}
else if (u=='4')
{RB5=RB6=1; RB4=RB7=0;}
else if (u=='5')
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{RB6=1; RB4=RB5=RB7=0;}
else if (u=='6')
{RB6=RB7=1;RB4=RB5=0;}
else if (u=='7')
{RB7=1;RB4=RB5=RB6=0;}
else if (u=='0')
{RB7=RB4=1; RB5=RB6=0;}
RB0 = 1; //This one is here because dc motor stops rotating when
stepper is on
//LM35 TEMPERATURE SENSOR
ADCON0=CHANNEL1;
//CHANNEL0=0b10000001 [CHANGEABLE]
lcd_goto(30);
read_adc();
temp=read_temp();
if (result>0b0100101000)//> 30
{
RD7=1;
}
else// if (result<0b100101100)// < 300
{RD7=0;
}
dis_num(temp/10);
30
send_char('.');
dis_num(temp%10);
send_char(0b11011111);
send_char('C');
delay(2000);
}
}
}
//==================subroutine LCD setting
===================================================
void send_config(unsigned char data)
{
RS=0;
lcd=data;
delay(500);
e_pulse();
}
void e_pulse(void)
{
E=1;
delay(500);
E=0;
delay(500);
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}
void send_char(unsigned char data)
{
RS=1;
lcd=data;
delay(500);
e_pulse();
}
void lcd_goto(unsigned char data)
{
if(data<16)
{
send_config(0x80|data);
// question: why is 0x80? Answer is simple remember bit 7 must be set for
//display.This is command to jump to specific address for display
}
else
{
data=data-20; //Write a Character to the Display at
the Current Cursor
//Position
send_config(0xc0|data);
}
}
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void lcd_clr(void)
{
RS=0;
send_config(0x01);
delay(600);
}
void dis_num(unsigned long data)
{
unsigned char hundred_thousand;
unsigned char ten_thousand;
unsigned char thousand;
unsigned char hundred;
unsigned char tenth;
hundred_thousand = data/100000;
data = data % 100000;
ten_thousand = data/10000;
data = data % 10000;
thousand = data / 1000;
data = data % 1000;
hundred = data / 100;
data = data % 100;
tenth = data / 10;
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data = data % 10;
if(hundred_thousand>0)
{
send_char(hundred_thousand + 0x30); //0x30 added to become ASCII code
send_char(ten_thousand + 0x30);
send_char(thousand + 0x30);
send_char(hundred + 0x30);
send_char(tenth + 0x30);
send_char(data + 0x30);
}
else if(ten_thousand>0)
{
send_char(ten_thousand + 0x30); //0x30 added to become ASCII code
send_char(thousand + 0x30);
send_char(hundred + 0x30);
send_char(tenth + 0x30);
send_char(data + 0x30);
}
else if(thousand>0)
{
send_char(thousand + 0x30); //0x30 added to become ASCII code
send_char(hundred + 0x30);
send_char(tenth + 0x30);
send_char(data + 0x30);
}
34
else if(hundred>0)
{
send_char(hundred + 0x30); //0x30 added to become ASCII code
send_char(tenth + 0x30);
send_char(data + 0x30);
}
else if(tenth>0)
{
send_char(tenth + 0x30); //0x30 added to become ASCII code
send_char(data + 0x30);
}
else send_char(data + 0x30); //0x30 added to become ASCII code
}
void increment(unsigned long data)
{
unsigned short j;
for(j=10;j>0;j--)
{ lcd_goto(32);
data=data+1;
dis_num(data);
delay(10000);
}
}
//==================subroutine ADC===========================
35
void read_adc(void)
{
unsigned short i;
unsigned long result_temp=0;
for(i=2000;i>0;i-=1) //looping 2000 times for getting average value
{
ADGO = 1; //ADGO is the bit 2 of the ADCON0 register
while(ADGO==1); //ADC start, ADGO=0 after finish ADC progress
result=ADRESH;
result=result<<8; //shift to left for 8 bit
result=result|ADRESL; //10 bit result from ADC
result_temp+=result;
}
result = result_temp/2000; //getting average value
}
unsigned short read_temp(void)
{
unsigned short temp;
temp=result;
return temp;
}
36
//==================subroutine DELAY=========================
void delay(unsigned short i)
{
for(;i>0;i--);
}
//==========================================================
char keypad_read2()
{
//setting row 1 high and others low while scanning the 3 columns
int a;
row_1 = 1;
row_2 = row_3 = row_4 = 0;
if (col_1 == 1)
{
a = '1';
return a;
}
else if (col_2 == 1)
{a = '2';
return a;
}
else if (col_3 == 1)
{a = '3';
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return a;
}
//setting row 2 high and others low while scanning the 3 columns
row_2 = 1;
row_1 = row_3 = row_4 = 0;
if (col_1 == 1)
{
a = '4';
return a;
}
else if (col_2 == 1)
{a = '5';
return a;
}
else if (col_3 == 1)
{a = '6';
return a;
}
//setting row 3 high and others low while scanning the 3 columns
row_3 = 1;
row_1 = row_2 = row_4 = 0;
if (col_1 == 1)
{
a = '7';
return a;
}
38
else if (col_2 == 1)
{a = '8';
return a;
}
else if (col_3 == 1)
{a = '9';
return a;
}
//setting row 4 high and others low while scanning the 3 columns
row_4 = 1;
row_1 = row_2 = row_3 = 0;
if (col_1 == 1)
{
a = '*';
return a;
}
else if (col_2 == 1)
{a = '0';
return a;
}
else if (col_3 == 1)
{a = '#';
return a;
}
else
a='-';
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return a;
}
//==========================================================
===========================================================
=========================================//=================
=========================================
40
The above codes have been developed on MPLAB IDE version 8.46 and was
successfully compiled and loaded on the Proteus hardware design. Simulation
results as shown previously contained both hardware and software simulations.
7.0 HARDWARE IMPLEMENTATION AND RESULTS:
==========================================================
8.0 DISCUSSION:
Among the difficulties faced in the project, the concept for analog to digital conversion had to be
revised throughout fully while the interfacing concept of keypad had also to be learnt. Before
going to the coding part, the keypad had to be broken down into smaller rows and columns and
activating one column by one and scanning the rows to see which key has been pressed. Thus
columns were connected as inputs to the PIC and rows as outputs. The coding was simulated on
41
MPLAB version 8.46 using embedded C programming as shown in the coding. keypad_read2()
function was thus made in order to detect which key has been pressed. Another problem
encountered was how to control a motor in 8 steps. Among the choices of either a servo or a
stepper motor, the unipolar stepper motor was chosen and a proper algorithm linking the keypad
pin pressed and angle moved by the motor was another problem to be solved. This was mainly
done by using functions to activate specific pins on the stepper motor whenever a pin is pressed
on the keypad. Moreover, enhancing the system by activating a buzzer when the temperature is
greater than 30 degrees Celsius was also included in the coding so as to render the system a more
complete one. Furthermore, the concept of using and LCD and its configuration were very
helpful as we may use it in 2 modes: nibble mode and 8 bit mode. Though nibble mode (4 bits)
uses less data lines, the 8 bit mode was preferred due to complexity issues.
9.0 CONCLUSION:
Thus, the work accomplished is a system which detects temperature using the analog pin with a
reference voltage and displayed on the lcd. Other new things learned about lcd is the usage of
either 5*7 dot matrix or 5*10 matrix. Other concepts learnt further helped to enhance actual
knowledge in such a way that as other bigger keypads can also be coded and interfaced as the
main concept still remains same and the control steps can be further increased by using other
stepper motors. LCDs can also be interfaced in the nibble mode and the coding was done
separately as a separate work to this project. The concept of using bipolar stepper motors was
also viewed before going for unipolar as it is more suitable for the specific application. Half
stepping technique was also viewed so as to increase number of steps and applied so as to match
the 8 required steps. Thus after grouping all the concepts, the PIC is the mastermind which does
all the data manipulations of the system while the LM35 sensor used (already calibrated) was
used for temperature sensor. LCD was used in 8 bit mode was made more user friendly and
guides the user throughout the process. Even the control step is also displayed on the LCD and
the angle the unipolar stepper motor is also available as shown in the hardware results. Linking
LCD concept and keypad concept though was a bit difficult, was finally solved. Though not used
in this project, other concepts like controlling brushless DC motor through a motor driver instead
of stepper motor was also gone through. Finally, the system was successfully accomplished as
planned and system is fully functional. Also increasing number of control steps can be done for
future improvements.
42
10.0 REFERENCES:
1. 2007, How stepper motors work [online], Images scientific instruments,
available from http://www.imagesco.com/articles/picstepper/02.html,
accessed on 28/01/12
2. Kiate, 2010, simple stepper motor calculator[online], Tutorials by citron
technologies, available from:
http://tutorial.cytron.com.my/2010/06/30/1835/, accessed on 28/01/12.
3. 2012, Datasheets- keypad input unit [online], Electronics in schools ltd,
available from: http://www.ectinschools.org/page.php?ps=2&p=927,
accessed on 28/01/12.
4. Lazaridis, G., 2010, simple unipolar stepper motor full step controller
[online], Electronic workbench pcb heaven, available from:
http://pcbheaven.com/circuitpages/Simple_Unipolar_Stepper_Motor_Full_S
tep_Controller/ accessed on 28/01/12.
5. Laidman, R., 2000, stepper motor and control[online], stepperworld.com,
available from:
http://www.stepperworld.com/Tutorials/pgBipolarTutorial.htm accessed on
28/01/2012
6. Table of ASCII characters[online], available from:
http://www.cs.mun.ca/~michael/c/ascii-table.html, accessed on 28/01/2012
7. Matrix keypad interfacing with PIC microcontroller[online],available from:
http://www.mcuexamples.com/PIC-Matrix-Keypad-tutorial.php , accessed
on 28/01/2012
8. Thoolen, S., 2011, Matrix keypad- driver[online], available from:
https://stefan.co/electronics/matrix-keypad-driver/, accessed on 28/01/2012