gsm to gsm voting

8/6/2019 Gsm to Gsm Voting

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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:


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:


INC cand3

CLR p3.5 ;buzzer

call delaylong

SETBp3.5SETBbitpass1

JMP ron3

la101:

JMP laj1

ron3:


INC cand4

CLR p3.5 ;buzzer

call delaylong

SETBp3.5

SETBbitpass1

JMP ron4

ron4:


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:


CJNE A,#07h,off


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CLR p3.5

call delaylong

SETBp3.5

;check the second number

recheck4:


MOV A,p2


INC cand1

CLR p3.5 ;buzzer

call delaylongSETBp3.5

JMP off1

laj1:

JMP laj100

off1:


INC cand2

CLR p3.5 ;buzzer

call delaylong

SETBp3.5

off2:


INC cand3

CLR p3.5 ;buzzer

call delaylong

SETBp3.5


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off3:


INC cand4

CLR p3.5 ;buzzer

call delaylong

SETBp3.5

off4:


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





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





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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
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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.

gsm to gsm voting

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