Design and development of ES to control switching of any appliance using
PIC 16F877A
Abstract:
It is experienced that many electrical devices like Television, computer, printer etc.
needs to be protected from its misuse by unauthorised persons. In the present paper an
Embedded System (ES) is designed and constructed to protect any electrical device from
its misuse by any unauthorised person. This ES is based on microcontroller(μC) PIC
16F877A of microchip. The PIC 16F877A microcontroller of microchip is used as a brain in
this ES. This μC receives password from keyboard and compares with true password. If
both are same then it will switch on the relay and the connected device will be on. If
password is incorrect then the μC will keep relay off and the device will remain off. The
password is changeable i.e. the user can change the password whenever it is required.
Introduction:
The control system to on-off any appliance can be designed by various logical
concepts. Few designs are based on two way switches. In this type of design few switches of
the key board needs to be put in on state to energise the relay. The main disadvantage of this
design is that if someone applies all possible combinations then it can be unlocked for any
one combination. [1,2] The another solution is design by pushbutton switches. The user has
to keep pressed all switches together. If somehow, the wrongly pressed switches are ignored
by ES then it is quite difficult to break the password. This type of design is better than
previous design using two way switches. [3] One another type of solution is to reset the
password by pressing wrong switch will make the password stronger than the previous
designs. To reset password by wrong key is a new logic and make open the lock for some
predetermined time.[4] The time restriction during password entering process will make the
system easy for fast users, but creates problem for slow users. In the present paper this
limited time span restriction is avoided. The user can take unlimited time to enter password.
Here the advance PIC microcontroller PIC 16F877A is used to design and construct
the ES to control the switching of any appliance through relay.
Microcontroller(PIC 16F877A):
A microcontroller (sometimes abbreviated μC, uC or MCU) is a small computer on
a single integrated circuit containing a processor core, memory, and programmable
input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also
often included on chip, as well as a typically small amount of RAM. Microcontrollers are
designed for embedded applications. Microcontrollers are used in automatically controlled
products and devices, such as automobile engine control systems, implantable medical
devices, remote controls, office machines, appliances, power tools, and other systems.[5]
Microcontroller used here is PIC16F877A.
The PIC 16F877A is enhanced flash microcontrollers. It is high performance RISC
type 40 pin DIP type CPU. It can work from D.C. to 20MHz frequency. It has 8K x 14 words
of flash program memory, 368 bytes of Data memory (RAM) and 256 bytes of EEPROM
data memory, 33 I/O pins, 8-channal 10-bit ADC, Two 8-bit and one 16-bit timers and two
comparators. Its operating voltage range is very wide from 2.0V to 5.5V.[6] The pin diagram of PIC
16F877A is shown in Fig.-1.
1
Fig.-1: Pin diagram of 16F877A
List of the components
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
1.
2.
3.
4.
7805 (+5 volt regulator) (1)
Programmed MCU PIC 16F877a with 40-pin DIP socket (1)
LT542 common Anode Seven Segment Displays (8)
Micro switches (24)
12MHz Crystal (1)
BC557 PNP Transistors (8)
0-9V, 500mA Transformer (1)
Four Diodes 1N4001(D1 to D4) (4)
470µF Electrolytic Capacitor (1)
0.1µF Box type Capacitor (1)
1KΩ Carbon Resistors (1)
10KΩ Carbon Resistors (8)
100Ω Carbon Resistors (9)
AN33 Opto coupler (1)
Relay(1)
Note: The figure in the parenthesis indicates the number of required components.
Circuit Description
The circuit can be explained by explaining the below given blocks of the ES.
Power Supply unit
Display unit
Keyboard unit
Switching unit
The Rr is connected between +5V and MCLR (Master Clear (Reset) input) and the 12MHz crystal is
connected between pins OSC1 and OSC2 of PIC 16F877A(U2).
2
Fig.-2 : Schematic diagram of ES
1. POWER SUPPY UNIT
Initial stage of every electronic circuit is power supply system which provides
required power to drive the whole system. The specification of power supply depends on
3
RB7
C
8
4
0
50 Hz
230 V A.C.
R10
T
0-9V
RB6
R1 to R8 = 10K
R9 to R16 = 100E
P2.7
R9
Bridge
-
_
P2.0
SSD7
RB1
RB0
RE2
RB2
gfa b h cde
RB3
7805
U1
RE1
Cin
1000micro
RB4
+
In
RB5
2
6
A
E
3
7
B
F
N
H
P
1
5
9
D
R12
R11
R14
R13
R16
R15
R
Enter
L
Chng
Out
SSD6
Rr
1K
Co
0.1micro
U2
SSD5
SSD4
baf g e dch
19 RD0/PSP0
20 RD1/PSP1
RC2/CCP1
18 RC3/SCK/SCL
17
15 RC0/T1OSO/T1CKI
16 RC1/T1OSI/CCP2
13 OSC1/CLKI
14 OSC2/CLKO
11 VDD
12 VSS
RE2/CS/AN7
SSD3
gfa b h cde
Q3
Q4
21
22
23
24
25
26
27
28
29
30
31
32
33
SSD2
SSD1
gfa b h cde
R4
Q2
R3
35
Q5
SSD0
baf g e dch
R8
R7
R6
R5
R2
36
34
R1
Q1
OC1
37
Rs
38
39
40
baf g e dch
RD2/PSP2
RD3/PSP3
RC4/SDI/SDA
RC5/SDO
RC6/TX/CK
RC7/RX/DT
RD4/PSP4
RD5/PSP5
RD6/PSP6
RD7/PSP7
VSS
VDD
9 RE1/WR/AN6
10
RB0/INT
RB1
RB2
RB3/PGM
RB4
RB5
RB6/PGC
RB7/PGD
8 RE0/RD/AN5
5 RA3/AN3/VREF+
6
RA4/T0CKI/C1OUT
7 RA5/AN4/SS/C2OUT
3 RA1/AN1
4 RA2/AN2/VREF-/CVREF
MCLR/VPP
2 RA0/AN0
1
gfa b h cde
X1
12MHz
baf g e dch
Gnd
Q6
Q7
Q8
RLY
LAMP
the power requirement and this requirement is determined by its rating. The main
components used in supply system are:
(IC 7805(U1))
The output of this regulated +5V power supply is connected with PIC. This Power
supply can be easily converted into +5V Uninterruptible Power Supply (UPS) by adding
12V/4.5Ah battery. This battery is useless in this application because any connected
electrical appliance needs high power and this battery can’t supply required power.[7,8] To
solve the power failure problem the high power UPS can be used with A.C. mains supply.
The Designed ES have used 9V/500mA Transformer. It means the maximum power
delivering capacity for this transformer is 9V x 500mA=4500mVA=4.5 Watt. While the ES
needs approximately 1W. This power requirement is negligible in comparison with any
electrical appliance.
2. Display unit
The microcontroller PIC 16F877A (U2) is used as a brain of this circuit in this project. The PIC
16F877A has five ports. Here Port-C and Port-D are used to scan 8-FNDs (8- seven segment LEDs).
Common anode type LT542 FNDs are used. The digit can be displayed on single FND by providing low
logic on its corresponding Port pin of Port-D and its corresponding special code on Port-C. The 8FNDs can be seen illuminated by scanning technique.
When low logic is given at the base of PNP transistor BC557 through 10KΩ resistor, then the
transistor comes into saturation. The saturated transistor provides +5 volt at the anode of its
corresponding FND. The scanning rate is set by internal Timer-1 of microcontroller PIC 16F877A.
The scanning of the eight FNDs is most important to understand. The eight PNP transistors BC
557 (T1 to T8) are doing switching during scanning process in all the eight FNDs. Each segment of
FND is connected with current limiting resistor. Eight current limiting resistors R9 to R16 of 100Ω are
used.
Fig.-3: bottom layer tracks for FNDs
Fig.-3 shows that the same track is not connected with the same segments in two consecutive
FNDs. The segments are the same for the same track in FND-0, FND-2, FND-4 and FND-6. Similarly,
the segments are the same for the same track in FND-1, FND-3, FND-5 and FND-7. By this logic in
P.C.B. drawing, the single sided P.C.B. is developed with novel queer multiplexing technique. But this
simplicity in P.C.B. drawing is making scanning software difficult. The Port-C needs to send different
data to display the same on two consecutive FNDs.[9,10]
The Port pins of Port-C are connected with the FND segments through eight 100Ω current
limiting resistors R9 to R16. The Port pins PC.7, PC.6, PC.5, PC.4, PC.3, PC.2, PC.1 and PC.0 are
connected with FND segments g, f, a, b, h, c, d and e respectively in FND-1, FND-3, FND-5 and FND-7.
4
Similarly, The Port pins PC.7, PC.6, PC.5, PC.4, PC.3, PC.2, PC.1 and PC.0 are connected with FND
segments b, a, f, g, e, d, c and h respectively in FND-0, FND-2, FND-4 and FND-6.[10]
The special codes to see the digit on FNDs are different for FND-0 and FND-1. The codes remain
same for FND-0, FND-2, FND-4 and FND-6. Similarly special codes remain same for FND-1, FND-3,
FND-5 and FND-7. These special codes are shown in Table-1.[10]
TABLE-1 : FND code for display
To see on FND
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
Blank
T
R
N
-(desh)
Special codes for
FND-1,FND-3,FND-5 & FND7
88H
EBH
4CH
49H
2BH
19H
18H
CBH
08H
09H
0AH
38H
9CH
68H
1CH
1EH
FFH
3CH
7EH
7AH
EFH
Special codes for
FND-0,FND-2,FND-4 & FND6
11H
7DH
23H
29H
DH
89H
81H
3DH
01H
09H
05H
C1H
93H
61H
83H
87H
FFH
C3H
E7H
E5H
7FH
3. Keyboard unit
The all eight pins of port-B and two pins of port-E are used for scanning of Key Board (KB).
The pin connections between the matrix KB and the MCU with key labels are shown in Table-2.
TABLE-2 : Port Pin connections of KB matrix with key functions
Port Pins
RB7
RB6
RB5
RB4
RB3
RB2
C
D
E
F
P
Chng
RB1
8
9
A
B
H
L
RB0
4
5
6
7
N
R
RE2
0
1
2
3
Enter
RE1
Table -2 shows that 24 keys are arranged in (4 x 6) matrix. In this matrix four rows
and six columns are arranged with scanning technique. This technique is very simple and
easily understood. The Timer-1 is also used to scan this keyboard.
4. Switching unit
This switching unit is most important and it is responsible to on and off the
connected appliance. The appliance will be switched on if correct password is entered. The
connected appliance can be switched off by switching off the ES. The port pin PE0 is
5
connected to relay through opto coupler(AN33). The relay is basically an electromechanical
switch which can turn on or turn off any connected electrical appliance. The 100Ω Resistor
(Rs) is current limiting resistor for opto coupler input.
Working of the device:
The display will show “dArsHAn” as we switch on the power. The connected
electrical appliance is remained switch off. The “Enter” key is used to enter the password
after pressing all keys combination (password). The ES is continuously ready to accept the
password. The manufacturer password is “01234567”. If we enter any other password
except “01234567” then display will show “PASS OFF” and the connected device (electric
bulb) will remain off. If we apply “01234567” as a password than the display will show “PASS
On” and the connected device will be switched on.
The “chng” key is used to change the password. The Password can be change by
below given procedure.
Step-1: Press “Chng” key to change the password. The display will show “OLD PASS”, i.e. the
ES demanding old password.
Step-2: Enter old password. If old password is correct than it will demand new password
otherwise it will not do any change.
Ster-3: Enter new password if entered old password is correct.
Step-4: the ES demands new password second time. Note: The display is not showing any
character but it shows ‘-‘. To overcome possibilities of wrong key depression the ES
demanding new password twice.
Step-5: Enter second time new password. If both passwords are same then it will change the
password. The display will show ‘changed’. Suppose both new passwords are different then
the password will remain unchanged and display will show ‘nochange’.
The display is not showing any characters but only displaying desh(‘-‘). This logic
allows keyboard of this ES to label in any language. The other people can’t recognize the
password.
Software
The program is written in ‘C’ language and compiled using MPLAB IDE V7.60
compiler. MPLAB IDE is freely available on https://www.microchip.com. The header file
htc.h is included to use the inbuilt functions of the software. Only Timer1 is used for display
multiplexing and keyboard scanning. The ‘Reset’ key is not put in the present hardware. All
other keys are scanned by the source program. The main task in this software development
is the time division multiplexing for displaying a particular number on the seven segment
display unit. The keyboard scanning is comparatively easy.
Applications :
This designed ES can be used for various applications. It can be used to turn on bulb
by password. It can be used to switched on Television, Room heater, Computer,
Printer/Scanner, Air conditioner, Microwave/Electrical oven etc. using password. This
password is easily changeable.
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[1]
[2]
[3]
[4]
[5]
[7]
[8]
[9]
[10]
Acknowledgement
I acknowledge a sincere thanks to shri. Pareshbhai Patel ( Lab. Assistant, Physics
Department, Hemchandracharya North Gujarat University, Patan ( Gujarat)) for his help
during this work. Any type of feedback from the reader will be accepted.
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http://electronicsforu.com/electronicsforu/circuitarchives/
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Electronics Projects Vol.-21, Published by EFY, PP-169.
A.Jeyabal,”simple Low-Cost Digital code lock”, Vol-31,No.-6, July-99
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Microcontroller (PIC16F72) with PWM”, International Journal of Engineering Research,
Volume No.1, Issue No.2, pp : 45-47.
[6]
http://ww1.microchip.com/downloads/en/DeviceDoc/39582C.pdf dated 21st
March,2014
Inderpreet Kaur, “Microcontroller Based Home Automation System With Security”,
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No.-3,September-2007, pp- 211 to 219
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