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Rachna College of Engineering and Technology
Gujranwala
Project Report
Intercom
(using AT89C2051)
Submitted to:
Engr. UsmanAslam
Submitted By:
Abubakar Butt
2011-EE-527
Faraz Ahmed Khan
2011-EE-566
Table of contents
1. Acknowledgement………………………………………………………………….. 3
2. Abstract ……………………………………………………………………………… 4
3. COMPONENTS…………………………………………….................................. 4
2.1 ULN 2003....................................................................................... 4
2.2 AT89C2051 MicrocontrollerDiscription…….………………………….. 6
2.2.1 AT89C2051 Features…………………………………………….. 6
2.2.2Pin Descript……………………………………………………… 7
2.3 MT2E Description ….. ……………………………………..…………... 8
2.3.1 Pin Description……………….…………………………………… 8
2.3.2 Internal Structure of MT2E …………………………………….... 8
2.4 DTM 8870decode………………………………………………….……9
4. Circuit diagram ……………………………………………………………………..11
5. WORKING………………………………………………………………………… 12
6. PROBLEM FACED……………………………………………………………….. 13
7. MARKET VALUE………………………………………………………………… 13
8. PROGRAM TO MAKE AINTERCOM…………………………........................ 13
9. Programme
10. Hex File ……………………………………………………………………………. 13
ACKNOWLEDGEMENT
To complete our this telephone based INTERCOM project we got help from a famous
site electrical4study.com. From this site we get the main idea of our project and also helpful
material related to our project. We also got help from our project incharge Engr. Muhammad
UsmanAslam. Who helped us to resolve our all problems regarding this project.
ABSTRACT
Our project is Intercom. This project is used as an electronic private exchange. It has two
telephones, which have the intercom facility, and they can be connected to the telephone line. All
the functions are controlled by the 8-bit microcontroller AT89C2051 which has an Program
Memory (ROM) of 2 kilobytes. The DTMF (Dual tone multiple frequency) signals are decoded
by the DTMF decoder IC 8870 and its output will be in decimal of the pressed key. The
switching functiond are done by 12v relays.
Components
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Microcontroller AT89C2051
IC ULN 2003
IC MCT 2E
IC MT 8870
Capacitors
Resistors
Relays
Oscillator
LED
ULN 2003
DESCRIPTION
The ULN2003 is a monolithic high voltage and high currentDarlington transistor arrays. It
consists of seven NPN darlingtonpairs that features high-voltage outputs with commoncathodeclamp diode for switching inductive loads. The collector-currentrating of a single
darlington pair is 500mA. The darlington pairsmay be parrlleled for higher current capability.
Applications includerelay drivers,hammer drivers, lampdrivers,display drivers(LED
gasdischarge),line drivers, and logic buffers.The ULN2003 has a 2.7kW series base resistor for
eachdarlington pair for operation directly with TTL or 5V CMOSdevices.
FEATURES
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500mA rated collector current (Single
(
output)
High-voltage
voltage outputs: 50V
Inputs compatibale with various types of logic.
Relay driver application_
AT89C2051
Description
The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer with 2K bytes
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 industrystandard MCS-51 instruction set. By combining a versatile 8-bit CPU with Flash on a monolithic
chip, the Atmel AT89C2051 is a power-ful microcomputer which provides a highly-flexible and
cost-effective solution to many embedded control applications. The AT89C2051 provides the
following standard features: 2K bytes of Flash, 128 bytes of RAM, 15 I/O lines, two 16-bit
timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, a precision
analog comparator, on-chip oscillator and clock circuitry. In addition, the AT89C2051 is
designed with static logic for opera-tion down to zero frequency and supports two software
selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM,
timer/counters, serial port and interrupt system to continue functioning. The power-down mode
saves the RAM contents but freezes the oscillator disabling all other chip functions until the next
hardware reset.
Features •
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2K Bytes of Reprogrammable Flash Memory – Endurance: 10,000 Write/Erase Cycles
2.7V to 6V Operating Range
Fully Static Operation: 0 Hz to 24 MHz
Two-level Program Memory Lock
128 x 8-bit Internal RAM
15 Programmable I/O Lines
Two 16-bit Timer/Counters
Six Interrupt Sources
Programmable Serial UART Channel
Direct LED Drive Outputs
On-chip Analog Comparator
Low-power Idle and Power-down Modes
Green (Pb/Halide-free) Packaging Option
PIN CONFIGURATION
BLOCK DIAGRAM
MCT 2E
 Gallium Arsenide Diode Infrared SourceOptically
SourceOptically Coupled to a Silicon NPN
Phototransistor
 High Direct-Current
Current Transfer Ratio
 Base Lead Provided for Conventional
 Transistor Biasing
 High-Voltage
Voltage Electrical Isolation . . .1.5-kV,
.1.5
or 3.55-kV Rating
 Plastic Dual-In-Line
Line Package
 High-Speed
Speed Switching:tr = 5 s, tf = 5 s Typical
 Designed to be Interchangeable with
 General Instruments MCT2 and MCT2E
DESCRIPTION
It contains optically coupled isolated consisting of gallium arsenide infrared emitting diode and
an NPN silicon phototransistor mounted in a 6 in dual line package.
package
PIN DESCRIPTION
INTERNAL STRUCTURE OF MCT 2E
DTMF DECODER (MT 8870)
Description
It is used for decoding the mobile signal. It gets DTMF tone from the telephone headset’s
speaker pins (here we used pin 1) at its Pin 2 & 3 and decodes the DTMF tone into 4-bit digital
signal which is fed to the 4:16 DECODER via Pins 11,12,13,14 & 15(StD).The DTMF Decoder
is operated with a 3.579MHz crystal (XTAL2) applied between Pin 7 and 8.In the DTMF receiver
MT8870 (IC), capacitor is used to filter the noise and the resistors R and R help to amplify the
input signal using the internal amplifier.Pin 16 connected to resistor R provides the early steering
output. It goes high immediately when the digital diagram detects a valid tone pair. Any
momentary loss of signal condition causes ESt to return to low state.Pin 17 connected to
capacitor U2 is bidirectional, acting as steering input/ guard time output (St/Gt). A voltage
greater than threshold of the steering logic VTSt detected at St causes the device to register the
detected tone pair. The guard time output resets the external steering time constant, and its state
is a function of ESt and the voltage at St.Pin 10 is kept high by Vcc. Pins 5,6,9 are grounded. Pin
1 & 4 is shorted.
Features
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Complete DTMF Receiver
Low power consumption
Internal gain setting amplifier
Adjustable guard time
Central office quality
Power-down mode
Inhibit mode
Backward compatible withMT8870C/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
BLOCK DIAGRAM
PIN DESCRIPTION
CIRCUIT DIAGRAM
WORKING
Intercom simply work on the switching of relays controlled by
microcontroller. Two phones are connected on the same telephone line. Both of them are
connected to MCT2E photocoupler when a receiver is pick up and any button is pushed from
any of the telephone it will deactivate the photocoupler and the photocoupler will send zero logic
on the output and send it to microcontroller. Decoder MT8870 receives input from relays which
is decoded and the output of 8870 is fed to the microcontroller and the output of microcontroller
is connected to the input of ULN2003 which in result turn off and on the respective relays and as
a result a ring bell is received on the other telephone.
PROBLEM FACED
In this project of telephone based intercom we faced many problems. At first chance we
faced the problem of the unavailability of the components on the software like proteus and
multisim then after that we faced the problem of unavailability of the components in the market.
After mounted on the breadboard we faced problem regarding relays and orthocoupler.
MARKET VALUE
The total cost of this project when we are making it first time is Rs. 2000 but when we are
preparing it on a larger scale the cost of this project is Rs. 1000.
PROGRAM TO MAKE A INTERCOM
INCLUDE REG_51
STD
Q3
Q2
Q1
Q0
EQU
P3.0
EQU
EQU
EQU
EQU
HOOK2 EQU
HOOK1 EQU
P3.7
P1.0
RING
TEL
TEL1
TEL2
P1.4
P1.7
P1.5
P1.6
EQU
EQU
EQU
EQU
P3.1
P3.2
P3.3
P3.4
DSEG
; This is internal data memory
ORG 20H ; Bit adressable memory
DTMF DATA 20H
D0 BIT DTMF.0
D1
BIT
DTMF.1
D2
BIT
DTMF.2
D3
BIT
DTMF.3
STACK: DS 1
; Stack begins here
CSEG
; Code begins here
;---------==========----------==========---------=========--------;
PROCESSOR INTERRUPT AND RESET VECTORS
;---------==========----------==========---------=========--------ORG 00H ; Reset
; ---------==========----------==========---------=========--------; Main routine
; ---------==========----------==========---------=========--------MOV SP,STACK
MOV P1,#00H
UUP:
CLR TEL
CLR TEL1
CLR TEL2
SETB HOOK1
SETB HOOK2
JNB HOOK1,TTEL1
JNB HOOK2,TTEL4
AJMP UUP
TTEL4: AJMP TTEL2
SXS11: AJMP SXS1
TTEL1: SETB TEL2
DCD1:
DCD3:
;CUT TEL 2
SETB STD
SETB HOOK1
JB HOOK1,UUP
JNB STD,DCD1
CALL READ
MOV A,DTMF
CJNE A,#01H,SXS11
SETB STD
JB STD,$
JB HOOK1,UUP
JNB STD,DCD3
CALL READ
MOV A,DTMF
CJNE A,#01H,SXS11
SETB TEL
SIGNAL
CLR TEL2
SETB TEL1
NOP
SETB RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CLR RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
SETB RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CLR RING
CALL DELAY
CLR TEL
CLR TEL1
CLR TEL2
;GIVE RING
CALL DELAY
SETB HOOK1
JNB HOOK1,$
uup1:
AJMP UUP
TTEL2: SETB TEL1
DCD2:
DCD4:
;CUT TEL 2
SETB STD
SETB HOOK2
JB HOOK2,UUP1
JNB STD,DCD2
CALL READ
MOV A,DTMF
CJNE A,#01H,SXS2
SETB STD
JB STD,$
JB HOOK2,UUP1
JNB STD,DCD4
CALL READ
MOV A,DTMF
CJNE A,#02H,SXS2
SETB TEL
SIGNAL
CLR TEL1
SETB TEL2
SETB RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CLR RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
SETB RING
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CALL DELAY
CLR RING
CALL DELAY
CLR TEL
CLR TEL1
CLR TEL2
;GIVE RING
CALL DELAY
SETB HOOK2
JNB HOOK2,$
AJMP UUP
SXS1:
SETB HOOK1
JNB HOOK1,$
CLR TEL2
AJMP UUP
;WAIT IF OTHER NUMBER DIALLED
SXS2:
SETB HOOK2
JNB HOOK2,$
CLR TEL1
AJMP UUP
;WAIT IF OTHER NUMBER DIALLED
DELAY:
MOV R5,#01H
REP3: MOV R0,#0FFH
REP2: MOV R1,#0FFH
REP1: NOP
DJNZ R1,REP1
DJNZ R0,REP2
DJNZ R5,REP3
RET
;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%
;
READ DTMF TONES
;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%
READ:
MOV DTMF,#00H
SETB Q0
SETB Q1
SETB Q2
SETB Q3
JNB Q0,VB1
SETB D0
VB1: JNB Q1,VB2
SETB D1
VB2: JNB Q2,VB3
SETB D2
VB3: JNB Q3,VB4
SETB D3
VB4: RET
;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%
END
HEX FILE
:03000000020800F3
:0C080000787FE4F6D8FD7581200200002E
:10000000852081759000C297C295C296D290D2B7D2
:1000100030900930B7020106017F01E1D296D2B0DB
:10002000D2902090E130B0FA3101E520B401EBD25A
:10003000B020B0FD2090CF30B0FA3101E520B401FE
:10004000D9D297C296D29500D29411F311F311F33D
:1000500011F311F3C29411F311F311F311F311F32E
:10006000D29411F311F311F311F311F3C29411F3BC
:10007000C297C295C29611F3D2903090FD0106D27C
:1000800095D2B0D2B720B7F530B0FA3101E520B43F
:100090000158D2B020B0FD20B7E330B0FA3101E50D
:1000A00020B40246D297C295D296D29411F311F39E
:1000B00011F311F311F3C29411F311F311F311F3CE
:1000C00011F3D29411F311F311F311F311F3C2945C
:1000D00011F3C297C295C29611F3D2B730B7FD01A2
:1000E00006D2903090FDC2960106D2B730B7FDC25D
:1000F0009501067D0178FF79FF00D9FDD8F9DDF57E
:1001000022752000D2B4D2B3D2B2D2B130B402D26E
:100110000030B302D20130B202D20230B102D203B7
:0101200022BC
:00000001FF