gsm to gsm voting
TRANSCRIPT
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PLATFORM USED
SOFTWARE REQUIREMENTS1. Batronix Prog Studio for programming of Microcontroller
2. Orcad for Circuit Designing
3. Pads for PCB designing
HARDWARE REQUIREMENTS
1. MICROCONTROLLER 89C51
2. CRYSTAL OSCILLATOR
3. RESISTOR
4. DIODE
5. CAPACITOR
6. CONNECTORS
7. RELAY
8. BUZZER
9. LIQUID CRYSTAL DISPLAY
10. GSM MOBILE PHONE
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Component list
HARDWARE REQUIREMENTS
1. MICROCONTROLLER 89C51
2. CRYSTAL OSCILLATOR
3. RESISTOR
4. DIODE
5. CAPACITOR
6. CONNECTORS
7. RELAY
8. BUZZER
9. LIQUID CRYSTAL DISPLAY
10. GSM MOBILE PHONE
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CIRCUIT DESCRIPTION
POWER SUPPLY SECTION:
Consists of:
1. RLMT Connector :- It is a connector used to connect the step down
transformer to the bridge rectifier.
2. Capacitor :-It is an electrolytic capacitor of rating 1000M/35V used to
remove the ripples. Capacitor is the component used to pass the ac and block
the dc.
3. Capacitor :-It is again an electrolytic capacitor 10M/65v used for filtering
to give pure dc.
4. Capacitor :- It is an ceramic capacitor used to remove the spikes generated
when frequency is high(spikes).
So the output of supply section is 5v regulated dc.
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MICROCONTROLLER SECTION:
Requires three connections to be successfully done for its operation to begin.
1. +5v supply: - This +5v supply is required for the controller to get start
which is provided from the power supply section. This supply is provided
at pin no. 20 of the 89c2051 controller.
2. Crystal Oscillator:- A crystal oscillator of 12 MHz is connected at pin
no.,x1 and pin no.,x2 to generate the frequency for the controller. Thecrystal oscillator works on piezoelectric effect.The clock generated is used
to determine the processing speed of the controller. Two capacitors are also
connected one end with the oscillator while the other end is connected with
the ground. As it is recommended in the book to connect two ceramic
capacitor of 20 pf40pf to stabilize the clock generated.
3. Reset section:- It consists of an rc network consisting of 10M/35V
capacitor and one resistance of 1k. This section is used to reset thecontroller connected at pin no.1 of AT89c51.
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DISPLAY SECTION
LCD(Liquid Crystal Display)
LCD is display screen of 16x2 which is used in this project. It has having 16
pin .
Pin no.1, pin no.16 and pin no.5 is connected to ground.
Pin no.2 and pin no.15 is connected to +5v.
Pin no.4 and pin no.6 are RS and EN respectively.
When something is to be displayed on LCD then RS should be 1
When command is generated for LCD then RS should be 0.
Pin no. 7 to 14 are connected with the microcontroller these pin are data lines.
Data to be written are sent via these data lines (D0-D7)
Pin no.3 is used for contrast control through two resistances.
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PCB LAYOUT
MAKING OF PRINTED CIRCUIT BOARD(PCB):-
Layout:-
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STEPS FOR MAKING PCB
Prepare the layout of the circuit (positive).
Cut the photofilm (slightly bigger) of the size of the layout.
Place the layout in the photoprinter machine with the photofilm above it. Make
sure that the bromide (dark) side of the film is in contact with the layout.
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Switch on the machine by pressing the push button for 5 sec.
Dip the film in the solution prepared (developer) by mixing the chemicals A &
B in equal quantities in water.
Now clean the film by placing it in the tray containing water for 1 min.
After this, dip the film in the fixer solution for 1 min. now the negative of the
Circuit is ready.
Now wash it under the flowing water.
Dry the negative in the photocure machine.
Take the PCB board of the size of the layout and clean it with steel wool to
make the surface smooth.
Now dip the PCB in the liquid photoresist, with the help of dip coat machine.
Now clip the PCB next to the negative in the photo cure machine, drying for
approximate 10-12 minute.
Now place the negative on the top of the PCB in the UV machine, set the timer
for about 2.5 minute and switch on the UV light at the top.
Take the LPR developer in a container and rigorously move the PCB in it.
After this, wash it with water very gently.
Then apply LPR dye on it with the help of a dropper so that it is completely
covered by it.
Now clamp the PCB in the etching machine that contains ferric chloride
solution for about 10 minutes.
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After etching, wash the PCB with water, wipe it a dry cloth softly.
Finally rub the PCB with a steel wool, and the PCB is ready
PROGRAMMING
INCLUDE 89c51.mc
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dtmf_dv EQU p2.4
EN EQU P3.2
RS EQU P3.3
main:
MOV R0,#"V"
call write_lcd
MOV R0,#"O"
call write_lcd
MOV R0,#"T"
call write_lcd
MOV R0,#"I"
call write_lcd
MOV R0,#"N"
call write_lcd
MOV R0,#"G"
call write_lcd
MOV R0,#" "
call write_lcd
MOV R0,#"M"
call write_lcd
MOV R0,#"A"
call write_lcd
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MOV R0,#"C"
call write_lcd
MOV R0,#"H"
call write_lcd
MOV R0,#"I"
call write_lcd
MOV R0,#"N"
call write_lcd
MOV R0,#"E"
call write_lcd
;******************************
; FOR GOING SECOND ROW
;******************************
MOV A,#C0H
call send_command
MOV R0,#"P"
call write_lcd
MOV R0,#"R"
call write_lcd
MOV R0,#"O"
call write_lcd
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MOV R0,#"C"
call write_lcd
MOV R0,#"E"
call write_lcd
MOV R0,#"S"
call write_lcd
MOV R0,#"S"
call write_lcd
MOV R0,#" "
call write_lcd
MOV R0,#"R"
call write_lcd
MOV R0,#"U"
call write_lcd
MOV R0,#"N"
call write_lcd
MOV R0,#"N"
call write_lcd
MOV R0,#"I"
call write_lcd
MOV R0,#"N"
call write_lcd
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MOV R0,#"G"
call write_lcd
mainloop:
JB p2.5 ,level1 ;check the ringCLR p3.5 ;buzzer
call delaylong
SETBp3.5
level1:
SETBp2.7 ;relay phone offhook
level0:
ron:
JNB dtmf_dv,la1
MOV A,p2
JB bitpass1,off
CJNE A,#0bh,off
CLR p3.5
call delaylong
SETBp3.5
recheck1:
JNB dtmf_dv,recheck1
MOV A,p2
CLR p3.5
call delaylong
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SETBp3.5
CJNE A,#07h,ron
JMP recheck2
ronnl12:
JMP ron
recheck2:
JNB dtmf_dv,recheck2
MOV A,p2
CLR p3.5
call delaylong
SETBp3.5
CJNE A,#01h,ron1;check the third numberINC cand1
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
SETBbitpass1
ron1:
CJNE A,#02h,ron2 ;check the third number
INC cand2
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
SETBbitpass1
JMP ron2
off:
JMP off100
la1:
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JMP la101
ronnl:
JMP ronnl12
ron2:
CJNE A,#03h,ron3 ;check the third number
INC cand3
CLR p3.5 ;buzzer
call delaylong
SETBp3.5SETBbitpass1
JMP ron3
la101:
JMP laj1
ron3:
CJNE A,#04h,ron4 ;check the third number
INC cand4
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
SETBbitpass1
JMP ron4
ron4:
CJNE A,#05h,ron5 ;check the third number
INC cand5
CLR p3.5 ;buzzer
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call delaylong
SETBp3.5
SETBbitpass1
ron5:
CJNE A,#06h,off100 ;check the third number
INC cand6
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
SETB bitpass1JMP mainloop
off100:
NOP
JB bitpass2,laj1
JNB dtmf_dv,laJ1
MOV A,p2
CJNE A,#0Ch,ronnl
CLR p3.5
call delaylong
SETBp3.5
recheck3:
JNB dtmf_dv,recheck3
CJNE A,#07h,off
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CLR p3.5
call delaylong
SETBp3.5
;check the second number
recheck4:
JNB dtmf_dv,recheck4
MOV A,p2
CJNE A,#01h,off1 ;check the third number
INC cand1
CLR p3.5 ;buzzer
call delaylongSETBp3.5
JMP off1
laj1:
JMP laj100
off1:
CJNE A,#02h,off2 ;check the third number
INC cand2
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
off2:
CJNE A,#03h,off3 ;check the third number
INC cand3
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
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off3:
CJNE A,#04h,off4 ;check the third number
INC cand4
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
off4:
CJNE A,#05h,off5 ;check the third number
INC cand5
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
off5:
CJNE A,#06h,laj1 ;check the third number
INC cand6
CLR p3.5 ;buzzer
call delaylong
SETBp3.5
laj100:
;******************************
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JB vot_stop,le1
JB bit_adm,lb1
JB p1.0,la01
INC cand1
CLR p3.5
call delaylong
SETBp3.5
JMP lb1
la01:
JB p1.1,la2
INC cand2
CLR p3.5call delaylong
SETBp3.5
SETBbit_adm
JMP lb1
la2:
JB p1.2,la3
INC cand3
CLR p3.5
call delaylong
SETBp3.5
SETBbit_adm
JMP lb1
la3:
JB p1.3,la4
INC cand4
CLR p3.5
call delaylong
SETBp3.5
SETBbit_adm
JMP lb1
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la4:
JB p1.4,la5
INC cand5
CLR p3.5
call delaylong
SETBp3.5
SETBbit_adm
JMP lb1
la5:
JB p1.5,la6
INC cand6
CLR p3.5call delaylong
SETBp3.5
SETBbit_adm
JMP lb1
la6:
le1:
lb1:
JB p1.6,lb2
CLR bit_adm
lb2:
JB p1.7,lb3
SETBvot_stop
CLR p3.5
call delaylong
SETBp3.5
MOV A,#C0H
call send_command
MOV R0,#"T"
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call write_lcd
MOV R0,#"O"
call write_lcd
MOV R0,#"T"
call write_lcd
MOV R0,#"A"
call write_lcd
MOV R0,#"L"call write_lcd
MOV R0,#" "
call write_lcd
MOV R0,#"V"
call write_lcd
MOV R0,#"O"
call write_lcd
MOV R0,#"T"
call write_lcd
MOV R0,#"E"
call write_lcd
MOV R0,#"S"
call write_lcd
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MOV R0,#" "
call write_lcd
JMP lc1
lb3:
JMP lb4
lc1:
MOV A,#00h
ADD A,CAND1
ADD A,CAND2
ADD A,CAND3ADD A,CAND4
ADD A,CAND5
ADD A,CAND6
MOV R0,A
MOV A,#CCH
call send_command
call write_lcd
;*******************************
; sub. for candidate voting
;*******************************
MOV A,#80H
call send_command
MOV R0,#"A"
call write_lcd
MOV A,#8cH
call send_command
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MOV R0,cand1
MOV A,#8eH
call send_command
call write_lcd
za1:
JB p1.7,za1
MOV A,#80H
call send_command
MOV R0,#"B"
call write_lcd
MOV A,#8cH
call send_command
MOV R0,cand2
MOV A,#8eH
call send_command
call write_lcd
za2:
JB p1.7,za2
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MOV A,#80H
call send_command
MOV R0,#"C"
call write_lcd
MOV A,#8cH
call send_command
MOV R0,cand3
MOV A,#8eH
call send_command
call write_lcd
za3:
JB p1.7,za3
MOV A,#80H
call send_command
MOV R0,#"D"
call write_lcd
MOV A,#8cH
call send_command
MOV R0,cand4
MOV A,#8eH
call send_command
call write_lcd
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za4:
JB p1.7,za4
MOV A,#80H
call send_command
MOV R0,#"E"
call write_lcd
MOV A,#8cH
call send_command
MOV R0,cand5
MOV A,#8eH
call send_commandcall write_lcd
za5:
JB p1.7,za5
MOV A,#80H
call send_command
MOV R0,#"F"
call write_lcd
MOV A,#8cH
call send_command
MOV R0,cand6
MOV A,#8dH
call send_command
call write_lcd
lb4:
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JMP mainloop
delaylong:
MOV regde,#250
de1:
NOP
NOP
NOP
NOP
NOP
NOPNOP
DJNZregde,de1
RET
write_lcd:
SETB rs
MOV p0,R0
SETB en
CLR en
RET
;**********************************************************
;subroutine for executing lcd command stored in A
;**********************************************************
send_command:
CLR rs
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MOV p0,A
SETB en
CLR en
RET
;**********************************************************
delay:
RET
Sensing unit
Sensing unit consists of mobile phone sensing IC 8870 whenever the circuit
receive call this IC provides interface between controller and mobile phone
whenever a key is pressed in a distant mobile phone that key is sensed in the IC
and IC further inform controller about the key pressed and further action can be
performed.
Description:
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The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the
band split filter and digital decoder functions. The filter section uses
switched capacitor techniques for high and low group filters; the decoder uses
digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-
bit code. External component count is minimized by on chip provision of a
differential input amplifier, clock oscillator and latched three-state bus interface.
Features
Complete DTMF Receiver
Low power consumption
Internal gain setting amplifier
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Adjustable guard time
Central office quality
Power-down mode
Inhibit mode
Backward compatible with
MT8870C/MT8870C-1
Applications
Receiver system for British Telecom (BT) or
CEPT Spec (MT8870D-1)
Paging systems
Repeater systems/mobile radio
Credit card systems
Remote control
Personal computers
Telephone answering machine
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Functional Description:
The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low
power consumption and high performance. Its architecture consists of a bandsplitfilter section, which separates the high and low group tones, followed by a digital
counting section which verifies the frequency and duration of the received tones
before passing the corresponding code to the output bus. Filter Section Separation
of the low-group and high group tones is achieved by applying the DTMF signal to
the inputs of two sixth-order switched capacitor bandpass filters, the bandwidths of
which correspond to the low and high group frequencies. The filter section also
incorporates notches at 350 and 440 Hz for exceptional dial tone rejection. Each
filter output is followed by a single order switched capacitor filter section which
smooth the signals prior to limiting. Limiting is performed by high-gain
comparators which are provided with hysteresis to prevent detection of unwanted
low-level signals. The outputs of the comparators provide full rail logic swings at
the frequencies of the incoming DTMF signals. Decoder Section Following the
filter section is a decoder employing digital counting techniques to determine the
frequencies of the incoming tones and to verify that they correspond to standard
DTMF frequencies. A complex averaging algorithm protects against tone
simulation by extraneous signals such as voice while
- Basic Steering Circuit providing tolerance to small frequency deviations and
variations. This averaging algorithm has been developed to ensure an optimum
combination of immunity to talk-off and tolerance to the presence of interfering
frequencies (third tones) and noise. When
the detector recognizes the presence of two valid tones (this is referred to as the
signal condition in some industry specifications) the Early Steering (ESt)
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output will go to an active state. Any subsequent loss of signal condition will cause
ESt to assume an inactive state (see Steering Circuit).
Steering Circuit:
Before registration of a decoded tone pair, the receiver checks for a valid signal
duration (referred to as character recognition condition). This check is performed
by an external RC time constant driven by ESt. A logic high on ESt causes vc to
rise as the capacitor discharges.
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MICROCONTROLLER UNITCONTROLLER AT89C51
Features
Compatible with MCS-51 Products
8K Bytes of In-System Re programmable Flash Memory
Endurance: 1,000 Write/Erase Cycles
Fully Static Operation: 0 Hz to 24 MHz
Three-level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Programmable Serial Channel
Low-power Idle and Power-down Modes
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DESCRIPTION
The AT89C52 is a low-power, high-performance CMOS 8-bit microcomputer
8Kbytes of Flash programmable and erasable read only memory (PEROM). The
device is manufactured using Atmel s high-density nonvolatile memory
technology and is compatible with the industry standard 80C51 and 80C52
instruction set and pin out.The on-chip Flash allows the program memory to be
reprogrammed in-system or by a Conventional nonvolatile memory programmer.
By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel
AT89C52 is a powerful microcomputer that provides a highly flexible and cost-
effective solution to many embedded control application.
The AT89C52 provides the following standard features: 8K bytes of Flash, 256
bytes of RAM, 32 I/O lines, three 16-bit timer/counters, a six-vector two-level
interrupt architecture, a full-duplex serial port, on-chip oscillator, and clock
circuitry. In addition, the AT89C52 is designed with static logic for operation
down to zero frequency and supports two software selectable power saving modes.
The Idle Mode tops the CPU while allowing the RAM; timer/counters, serial port.
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Pin Description
VCCSupply voltage.
GND
Ground.Port 0
Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can
sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as
high impedance inputs.
Port 0 can also be configured to be the multiplexed low order address/data bus
during accesses to external program and data memory. In this mode, P0 has
internal pull-ups .
Port 0 also receives the code bytes during Flash programming and outputs the code
bytes during program verification. External pull-ups are required during program
verification.
Port 1
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output
buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they
are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1
pins that are externally being pulled low will source current (IIL) because of the
internal pull-ups.
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In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external
count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX),
respectively, as shown in the following table.
Port 1 also receives the low-order address bytes during
Port 2
Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output
buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they
are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2
pins that are externally being pulled low will source current (IIL) because of the
internal pull-ups. Port 2 emits the high-order address byte during fetches from
external program memory and during accesses to external data memory that use16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal
pull-ups when emitting 1s. During accesses to external data memory that use 8-bit
addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function
Register. Port 2 also receives the high-order address bits and some control signals
during Flash programming and verification.
Port 3
Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output
buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they
are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3
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pins that are externally being pulled low will source current (IIL) because of the
pull-ups. Port 3 also serves the functions of various special features of the
AT89C51, as shown in the following table. Port 3 also receives some control
signals for Flash programming.
RST
Reset input. A high on this pin for two machine cycles while the oscillator is
running resets the device.
ALE/PROG
Address Latch Enable is an output pulse for latching the low byte of the address
during accesses to external memory. This pin is also the program pulse input
(PROG) during Flash programming. In normal operation, ALE is emitted at aconstant rate of 1/6 the oscillator frequency and may be used for external timing or
clocking purposes. Note, however, that one ALE pulse is skipped during each
access to external data memory. If desired, ALE operation can be disabled by
setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a
MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the
ALE-disable bit has no effect if the micro controller is in external execution mode.
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PSEN
Program Store Enable is the read strobe to external program memory. When theAT89C52 is executing code from external program memory, PSEN is activated
twice each machine cycle, except that two PSEN activations are skipped during
each access to external data memory.
EA/VPP
External Access Enable. EA must be strapped to GND in order to enable the device
to fetch code from external program memory locations starting at 0000H up to
FFFFH.
Note, however, that if lock bit 1 is programmed, EA will be internally latched on
reset.
EA should be strapped to VCC for internal program executions. This pin also
receives the 12-volt programming enable voltage (VPP) during Flash programmingwhen 12-volt programming is selected.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating
circuit.
XTAL2
Output from the inverting oscillator amplifier .
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Oscillator Characteristics
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XTAL1 and XTAL2 are the input and output, respectively, of an inverting
amplifier that can be configured for use as an on-chip oscillator, as shown in
Figure 7. Either a quartz crystal or ceramic resonator may be used. To drive the
device from an external clock source, XTAL2 should be left
Un connected while XTAL1 is driven, as shown in Figure 8.There are no
requirements on the duty cycle of the external clock signal, since the input to the
internal clocking circuitry is through a divide-by-two flip-flop, but minimum and
maximum voltage high and low time specifications must be observed.
Idle Mode
In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain
active. The mode is invoked by software. The content of the on-chip RAM and all
the special functions registers remain unchanged during this mode. The idle mode
can be terminated by any enabled interrupt or by a hardware reset.
Note that when idle mode is terminated by a hardware reset, the device normally
resumes program execution from where it left off, up to two machine cycles before
the internal reset algorithm takes control. On-chip hardware inhibits access tointernal RAM in this event, but access to the port pins is not inhibited. To eliminate
the possibility of an unexpected write to a port pin when idle mode is terminated
by a reset, the instruction following the one that invokes idle mode should not
write to a port pin or to external memory.
Power-down Mode
In the power-down mode, the oscillator is stopped, and the instruction that invokes
power-down is the last instruction executed. The on-chip RAM and Special
Function Registers retain their values until the power-down mode is terminated.
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The only exit from power-down is a hardware reset. Reset redefines the SFR s but
does not change the on-chip RAM. The reset should not be cultivated before VCC
is restoredto its normal operating level and restart and stabilize.must be held active
long enough to allow the oscillator to
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Liquid crystal display(LCD)
A liquid crystal display (commonly abbreviated LCD) is a thin, flat display device
made up of any number of color ormonochromepixels arrayed in front of a light
source orreflector. It is prized by engineers because it uses very small amounts of
electric power, and is therefore suitable for use in battery-powered electronic
devices. Each pixel of an LCD consists of a layer ofperpendicular molecules
aligned between two transparent electrodes, and twopolarizingfilters, the axes ofpolarity of which are perpendicular to each other. With no liquid crystal between
the polarizing filters, light passing through one filter would be blocked by the
electrodes. The surfaces of the electrodes that are in contact with the liquid crystal
material are treated so as to align the liquid crystal molecules in a particular
direction. This treatment typically consists of a thin polymer layer that is
unidirectionally rubbed using a cloth (the direction of the liquid crystal alignment
is defined by the direction of rubbing). Before applying an electric field, the
orientation of the liquid crystal molecules is determined by the alignment at thesurfaces. In a twisted nematic device (the most common liquid crystal device), the
surface alignment directions at the two electrodes are perpendicular, and so the
molecules arrange themselves in a helical structure, or twist. Because the liquid
crystal material isbirefringent, light passing through one polarizing filter is rotated
by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to
pass through the second polarized filter. Half of the light is absorbed by the first
polarizing filter, but otherwise the entire assembly is transparent. When a voltage
is applied across the electrodes, a torque acts to align the liquid crystal moleculesparallel to the electric field, distorting the helical structure (this is resisted by
elastic forces since the molecules are constrained at the surfaces). This reduces the
rotation of the polarization of the incident light, and the device appears gray. If the
applied voltage is large enough, the liquid crystal molecules are completely
untwisted and the polarization of the incident light is not rotated at all as it passes
http://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Monochromehttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Reflectorhttp://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Filterhttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Birefringencehttp://en.wikipedia.org/wiki/Transparenthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electrodeshttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Parallelhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/w/index.php?title=Elastic_forces&action=edithttp://en.wikipedia.org/wiki/Constrainedhttp://en.wikipedia.org/wiki/Grayhttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Monochromehttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Reflectorhttp://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Filterhttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Birefringencehttp://en.wikipedia.org/wiki/Transparenthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electrodeshttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Parallelhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/w/index.php?title=Elastic_forces&action=edithttp://en.wikipedia.org/wiki/Constrainedhttp://en.wikipedia.org/wiki/Gray -
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through the liquid crystal layer. This light will then be polarized perpendicular to
the second filter, and thus be completely blocked and thepixel will appearblack.
By controlling the voltage applied across the liquid crystal layer in each pixel, light
can be allowed to pass through in varying amounts, correspondingly illuminating
the pixel. With a twisted nematic liquid crystal device it is usual to operate thedevice between crossed polarizers, such that it
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COMPARISON BETWEEN TRANSISTORS & RELAYS
Advantages of relays:
Relays can switch AC and DC, transistors can only switch DC.
Relays can switch high voltages, transistors cannot.
Relays are a better choice for switching large currents (> 5A).
Relays can switch many contacts at once.
Disadvantages of relays:
Relays are bulkier than transistors for switching small currents.
Relays cannot switch rapidly (except reed relays), transistors can switch
many times per second.
Relays use more power due to the current flowing through their coil.
Relays require more current than many chips can provide, so a low power
transistor may be needed to switch the current for the relay's coil.
Crystal Oscillator
It is often required to produce a signal whose frequency or pulse rate is very stable
and exactly known. This is important in any application where anything to do with
time or exact measurement is
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crucial. It is relatively simple to make an oscillator that produces some sort of a
signal, but another matter to produce one of relatively precise frequency and
stability. AM radio stations must have a carrier frequency accurate within 10Hz of
its assigned frequency, which may be from 530 to 1710 kHz. SSB radio systems
used in the HF range (2-30 MHz) must be within 50 Hz of channel frequency for
acceptable voice quality, and within 10 Hz for best results. Some digital modes
used in weak signal communication may require frequency stability of less than 1
Hz within a period of several minutes. The carrier frequency must be known to
fractions of a hertz in some cases. An ordinary quartz watch must have an
oscillator accurate to better than a few parts per million. One part per million will
result in an error of slightly less than one half second a day, which would be about
3 minutes a year. This might not sound like much, but an error of 10 parts per
million would result in an error of about a half an hour per year. A clock such as
this would need resetting about once a month, and more often if you are the
punctual type. A programmed VCR with a clock this far off could miss the
recording of part of a TV show. Narrow band SSB communications at VHF and
UHF frequencies still need 50 Hz frequency accuracy. At 440 MHz, this is slightly
more than 0.1 part per million.
Ordinary L-C oscillators using conventional inductors and capacitors can achieve
typically 0.01 to 0.1 percent frequency stability, about 100 to 1000 Hz at 1 MHz.
This is OK for AM and FM broadcast receiver applications and in other low-end
analog receivers not requiring high tuning accuracy. By careful design and
component selection, and with rugged mechanical construction, .01 to 0.001%, or
even better (.0005%) stability can be achieved. The better figures will undoubtedly
employ temperature compensation components and regulated power supplies,
together with environmental control (good ventilation and ambient temperature
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regulation) and battleship mechanical construction. This has been done in some
communications receivers used by the military and commercial HF communication
receivers built in the 1950-1965 era, before the widespread use of digital
frequency synthesis. But these receivers were extremely expensive, large, and
heavy. Many modern consumer grade AM, FM, and shortwave receivers
employing crystal controlled digital frequency synthesis will do as well or better
from a frequency stability standpoint.
An oscillator is basically an amplifier and a frequency selective feedback network
(Fig 1). When, at a particular frequency, the loop gain is unity or more, and the
total phaseshift at this frequency is zero, or some multiple of 360 degrees, the condition
for oscillation is satisfied, and the circuit will produce a periodic waveform of this
frequency. This is usually a sine wave, or square wave, but triangles, impulses, or
other waveforms can be produced. In fact, several different waveforms often are
simultaneously produced by the same circuit, at different points. It is also possible
to have several frequencies produced as well, although this is generally
undesirable.
CAPACITOR
A capacitor or condenser is apassiveelectronic component consisting of a pair ofconductors separated by a dielectric (insulator). When a potential difference
(voltage) exists across the conductors, an electric field is present in the dielectric.
This field stores energy and produces a mechanical force between the conductors.
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The effect is greatest when there is a narrow separation between large areas of
conductor, hence capacitor conductors are often called plates.
An ideal capacitor is characterized by a single constant value, capacitance, which
is measured in farads. This is the ratio of the electric charge on each conductor to
the potential difference between them. In practice, the dielectric between the plates
passes a small amount of leakage current. The conductors and leads introduce an
equivalent series resistance and the dielectric has an electric field strength limit
resulting in abreakdown voltage.
RESISTOR
Resistors are used to limit the value of current in a circuit. Resistors offer
opposition to the flow of current. They are expressed in ohms for which the symbol
is . Resistors are broadly classified as
(1)Fixed Resistors
(2)Variable Resistors
Fixed Resistors :
The most common of low wattage, fixed type resistors is the molded-carbon
composition resistor. The resistive material is of carbon clay composition. The
leads are made of tinned copper. Resistors of this type are readily available in
value ranging from few ohms to about 20M , having a tolerance range of 5 to
20%. They are quite inexpensive. The relative size of all fixed resistors changes
with the wattage rating.
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Another variety of carbon composition resistors is the metalized type.
It is made by deposition a homogeneous film of pure carbon over a glass, ceramic
or other insulating core. This type of film-resistor is sometimes called the precision
type, since it can be obtained with an accuracy of 1%.
Lead Tinned Copper Material
Colour Coding Molded Carbon Clay Composition
Fixed Resistor
Coding Of Resistor :
Some resistors are large enough in size to have their resistance printed on the
body. However there are some resistors that are too small in size to have numbers
printed on them. Therefore, a system of colour coding is used to indicate their
values. For fixed, moulded composition resistor four colour bands are printed on
one end of the outer casing. The colour bands are always read left to right from the
end that has the bands closest to it. The first and second band represents the first
and second significant digits, of the resistance value. The third band is for the
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number of zeros that follow the second digit. In case the third band is gold or
silver, it represents a multiplying factor of 0.1to 0.01. The fourth band represents
the manufactures tolerance.
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RESISTOR COLOUR CHART
For example, if a resistor has a colour band sequence: yellow, violet, orange and
gold
5 green
0 black
1 brown
2 red
3 orange
4 yellow
6 blue
7 purple
8 silver
9 white
0 black
1 brown
2 red
3 orange
4 yellow
6 blue
7 purple
8 silver
9 white
5green
5 green
0 black
1 brown
2 red
3 orange
4 yellow
6 blue
7 purple
8 silver
9 white
5 green
0 black
1 brown
2 red
3 orange
4 yellow
6 blue
7 purple
8 silver
9 white
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Then its range will be
Yellow=4, violet=7, orange=10, gold=5% =47K 5% =2.35K
Most resistors have 4 bands:
The first band gives the first digit.
The second band gives the second digit.
The third band indicates the number of zeros.
The fourth band is used to show the tolerance (precision) of the resistor.
This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000 = 270 k .
The standard colour code cannot show values of less than 10 . To show these
small values two special colours are used for the third band: gold, which means
0.1 and silver which means 0.01. The first and second bands represent the
digits as normal.
For example:
red, violet, gold bands represent 27 0.1 = 2.7
blue, green, silverbands represent 56 0.01 = 0.56
The fourth band of the colour code shows the tolerance of a resistor. Tolerance is
the precision of the resistor and it is given as a percentage. For example a 390
resistor with a tolerance of 10% will have a value within 10% of 390 , between
390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390).
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A special colour code is used for the fourth band tolerance:
silver10%, gold 5%, red 2%, brown 1%.
If no fourth band is shown the tolerance is 20%.
LED (LIGHT EMITTING DIODE)
A junction diode, such as LED, can emit light or exhibit electro luminescence.
Electro luminescence is obtained by injecting minority carriers into the region of a
pn junction where radiative transition takes place. In radiative transition, there is a
transition of electron from the conduction band to the valence band, which is made
possibly by emission of a photon. Thus, emitted light comes from the hole electron
recombination. What is required is that electrons should make a transition from
higher energy level to lower energy level releasing photon of wavelength
corresponding to the energy difference associated with this transition. In LED the
supply of high-energy electron is provided by forward biasing the diode, thus
injecting electrons into the n-region and holes into p-region.
The pn junction of LED is made from heavily doped material. On forward bias
condition, majority carriers from both sides of the junction cross the potential
barrier and enter the opposite side where they are then minority carrier and cause
local minority carrier population to be larger than normal. This is termed as
minority injection. These excess minority carrier diffuse away from the junction
and recombine with majority carriers.
In LED, every injected electron takes part in a radiative recombination and
hence gives rise to an emitted photon. Under reverse bias no carrier injection takes
place and consequently no photon is emitted. For direct transition from conduction
band to valence band the emission wavelength.
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In practice, every electron does not take part in radiative recombination and
hence, the efficiency of the device may be described in terms of the quantum
efficiency which is defined as the rate of emission of photons divided by the rate of
supply of electrons. The number of radiative recombination, that take place, is
usually proportional to the carrier injection rate and hence to the total currentflowing.
LED Materials:
One of the first materials used for LED is GaAs. This is a direct band gap material,
i.e., it exhibits very high probability of direct transition of electron from
conduction band to valence band. GaAs has E= 1.44 eV. This works in the infrared
region.
Gallium Arsenide Phosphide is a tertiary alloy. This material has a special feature
in that it changes from being direct band gap material.
Blue LEDs are of recent origin. The wide band gap materials such as GaN are one
of the most promising LEDs for blue and green emission. Infrared LEDs are
suitable for optical coupler applications.
ADVANTAGES OF LEDs:
1. Low operating voltage, current, and power consumption makes Leds
compatible with electronic drive circuits. This also makes easier interfacing
as compared to filament incandescent and electric discharge lamps.
2. The rugged, sealed packages developed for LEDs exhibit high resistance to
mechanical shock and vibration and allow LEDs to be used in severeenvironmental conditions where other light sources would fail.
3. LED fabrication from solid-state materials ensures a longer operating
lifetime, thereby improving overall reliability and lowering maintenance
costs of the equipment in which they are installed.
4. The range of available LED colours-from red to orange, yellow, and green-
provides the designer with added versatility.
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5. LEDs have low inherent noise levels and also high immunity to externally
generated noise.
6. Circuit response of LEDs is fast and stable, without surge currents or the
prior warm-up, period required by filament light sources.
7. LEDs exhibit linearity of radiant power output with forward current over a
wide range.
LEDs have certain limitations such as:
1. Temperature dependence of radiant output power and wave length.
2. Sensitivity to damages by over voltage or over current.
3. Theoretical overall efficiency is not achieved except in special
cooled or pulsed conditions.