DTMF12

8/13/2019 DTMF12

1/48

DUAL TONE MULTI FREQUENCY (DTMF) REMOTE CONTROL SYSTEM

A PROJECT REPORT

Submitted by

SANTOSH.G (41502105062)

VARUN.D (41502105082)

ROOP KUMAR.P (41502105503)

RAMA KONDA REDDY.L (41502105504)

in partial fulfillment for the award of the degree

of

BACHELOR OF ENGINEERING

in

ELECTRICAL AND ELECTRONICS ENGINEERING

SRM ENGINEERING COLLEGE,KATTANKULATHUR-603 203, KANCHEEPURAM DISTRICT.

ANNA UNIVERSITY: CHENNAI 600 025

APRIL 2006

8/13/2019 DTMF12

2/48

ANNA UNIVERSITY: CHENNAI 600 025

BONAFIDE CERTIFICATE

Certified that this project report DUAL TONE MULTI FREQUENCY (DTMF)

REMOTE CONTROL SYSTEM is the bonafide work of SANTOSH.G

(41502105062), VARUN.D (41502105082), ROOP KUMAR.P (41502105503), RAMA

KONDA REDDY.L (41502105504)

who carried out the project work under my supervision.

Signature of HOD Signature of supervisor

Prof.R.CHIDAMBARAM Ms.K.S.VIDHYA

HEAD OF THE DEPARTMENT Lecturer

Electrical And Electronics Engineering Electrical and Electronics Engineering

S.R.M.Engineering College S.R.M.Engineering College

Kattankulathur-603 203 Kattankulathur-603 203

Kancheepuram District Kancheepuram District

Signature of Internal Examiner Signature of External Examiner

8/13/2019 DTMF12

3/48

ACKNOWLEDGEMENT

We take sincere efforts to acknowledge the guidance and the advice of all the people

who have helped us in completing this project successfully.

We grab this opportunity to thank our revered director Dr.T.P.Ganesan, for

providing us with an opportunity to carry on with the project.

We take immense pleasure in expressing our thanks to our respected Principal,

Prof.R.Venkataramani,who has alwaysbeen a source of inspiration for all of us.

We are greatly obliged to Prof.R.Chidambaram, Head of Department, Electrical

and Electronics Engineering for his constant encouragement throughout the course of our

project.

We express our gratitude to our guide Ms.K.S.Vidhya, Lecturer, Department of

Electrical and Electronics Engineering, for her guidance and timely suggestions that helped

us go through the tough times in our project work.

ABSTRACT

Remote control through the telephone line is an interesting proposition. Although

the concept is new, and control circuits based on the same were developed almost ten yearsback, it is however became more popular with the introduction of Dual-Tone Multi-

Frequency (DTMF) mode of dialing. Single-chip DTMF encoders/decoders are available

today, which make the designing of such systems easy and reliable.

The switching unit described here is capable of controlling up to 7 mains-powered

loads with aid of commands received via telephone. Any tone dialing (DTMF) telephone set

or hand-held tone dialer may be used to send commands to the switching units. With

personal access code.

8/13/2019 DTMF12

4/48

The circuit is connected to the telephone network just like any normal telephone set.

On being called, the circuit waits a predetermined number of ring signals, and then answers

the call (electrically, it lifts the receiver). Next, it waits for a pre-programmed system access

code. Reception of the correct system code is acknowledged with a short tone, which the

caller can hear. Next, load number 1, for instance, a coffee machine can be switched on by

pressing the 1 key twice. The same can be switched off by dialing 1 and then 0. The

status of the load 1 (on/off) may be called up by pressing 1 and then 2 on the DTMF

keypad. The control of the other six loads is identical to that of load 1, i.e., the channel

(load) number is dialed first, then 0 or 1 for switching off or on, or 2 to request the

channel status. An exception is formed by number 8: dialing this number allows you to

switch all channels on/off simultaneously. On/off status requesting does not work in this

mode.

LIST OF TABLES

T.No. TITLE PAGE No.3.1 FUNCTIONAL DECODE TABLE 14

LIST OF FIGURES

F.No. TITLE PAGE No.

1.1 DIFFERENT TELEPHONELINE CONDITIONS 2

1.2 STANDARD DTMF FREQUENCY SPECTRUM 3

1.3 DTMF KEYPAD MATRIX 4

2.1 GENERAL BLOCK DIAGRAM 7

3.1 FUNCTIONAL BLOCK DIAGRAM OF DTMF IC 11

3.2 STEERING CIRCUIT 13

4.1 MASTER UNIT CIRCUIT 17

4.2 RELAY CIRCUIT 20

4.3 POWER SUPPLY CIRCUIT 21

8/13/2019 DTMF12

5/48

1. INTRODUCTION

The aim of the project is to control the home appliances through a telephone

(DTMF telephone) line. So, first let us know the basics of the telephone line and DTMF

signaling.

1.1 Basic Telephone Line

A telephone line basically carries voice and various signaling information between

the subscriber telephone instrument and exchange. Suitable protection circuitry on both

ends of the line protects the exchange equipment and the telephone instrument against

damage from lightning, high-voltage transients and polarity reversal. Signaling information is

required to inform the subscriber and exchange about on-hook, off-hook, busy/not busy

and out of orderconditions of the telephone/line. The ringing signal from the exchange to

the subscriber is of 70-90V RMS, 20-25Hz.

The outgoing signal refers to signals reaching the exchange from the subscribers

telephone, indicating on-hook, off-hook, hang-up dialing etc. Outgoing signals can be of two

types: Line signaling and Register signaling. Line signaling encompasses on-hook, off-

hook, hang-up state signals, while register signaling refers to dialing, where in digits of the

destination or the called party are passed on to the exchange for establishing a connection.

When the telephone is in on-hook condition, the cradle switch is in open condition.

There is no flow of current in the telephone circuit. When the telephone handset is lifted off

the cradle, the cradle switch closes to form a closed-loop circuit with the exchange battery

and the telephone circuit. This circuit is also referred to as local loop circuit. Exchange

battery voltage is typically 48V. The loop current is used by the exchange to establish

on/off-hook status of the telephone. (If the loop current is 13.5mA to 60mA the exchange

detects it as off-hook condition, and if the loop current is less than 7.5mA the exchange

interprets it as on-hook condition.)

Different line conditions are depicted in the figure.1. The open circuit line voltage is

about 50V DC. Incoming voice voltage to the telephone instrument varies from 0.5V to 1V

and the maximum outgoing voice voltage is about 2V RMS. The ringing signal is 70-90V

RMS at 20-25Hz. In pulse dialing telephones, register signaling is known as DC loop

signaling. In this case, the dialed number is conveyed to the exchange by make and break

of the loop circuit.

8/13/2019 DTMF12

6/48

1.2 DTMF Signaling

AC register signaling is used in DTMF telephones. Here, tones rather than

make/break pulses are used for dialing. Each dialed digit is uniquely represented by a pair of

sine wave tones. These tones (one from lower group for row and other from high group for

column) are sent to the exchange when a digit is dialed by pushing the key. These tones lie

within the speech band of 300 to 3400Hz, and are chosen so as to minimize the possibility

of any valid frequency pair existing in the normal speech simultaneously. Actually, this

minimization is made possible by forming pairs with one tone from the higher group and the

other from the lower group of frequencies. The DTMF spectrum is shown in the figure.2.

A valid DTMF signal is the sum of two tones, one from the lower group (697-

941Hz) and the other from the higher group (1209-1663). Each group contains four

individual tones. The DTMF signaling scheme is shown in figure.3. This scheme allows 16

unique combinations. Ten of these codes represent digits 0 through 9. The remaining six are

reserved for special purpose dialing.

Tones in the DTMF dialing are so chosen that none of the tones is harmonic of any

other tone. Therefore there is no chance of distortion caused by harmonics. Each tone is

sent as long as the key remains pressed.

The DTMF coding scheme ensures that each signal contains only one component

from each of the high and low groups. This significantly simplifies decoding because the

f(Hz)

LOGARITHMIC

TONESGENERATEDFROMATELEPHONETYPICALLYHAVE-2dBTWIST

(PRE-EMPHASIS)APPLIEDTOCOMPENSATEFORHIGHFREQUENCY

ROLLOFFALONGTHETELEPHONELINE.

DCBA2dB

AMPLITUDE

16331477133612099418527706971659

16071501

14531358

131412291189957925

867837784756709685

Figure1.2StandardDTMFfrequencyspectrum+(1.5%+2Hz).Secondharmonicsofthelowgroup(possiblycreateddue

toanon-linearchannel)fallwithinthepassbandofhighgroup(indicatedbyA,B,C,D).Thisisapotentialsourceof

interference.

8/13/2019 DTMF12

7/48

composite DTMF signal may be separated with band pass filters into single frequency

components, each of which may be handled individually. As a result, the DTMF coding

scheme is a flexible signaling scheme with high reliability, hence motivating innovative and

competitive decoder design.

1.3 Microcontroller Systems

Microcontrollers (MCUs) are intelligent electronic devices used for performing

operations. They deliver functions similar to those performed by a microprocessor (CPU)

inside a computer. MCUs are slower and can address less memory than CPUs, but are

designed for real-world control problems.

The microcontroller used here is AT89C51 which is one of the members of family of

8051microcontroller. So, let us know first about the 8051 microcontroller.

1.3.1 A brief history of the 8051

In 1981, Intel Corporation introduced an 8-bit microcontroller called the 8051. This

microcontroller had 128 bytes of RAM , 4K bytes of on-chip ROM, two timers, one serial

port, and four ports (each 8-bits wide) all on a single chip. At the time it was also referred to

as a system on a chip. The 8051 is an 8-bit processor, meaning that the CCPU can work

only 8 bits of data at a time. Data larger than 8 bits has to be broken in to 8-bit pieces to be

processed by the CPU. The 8051 has a total of four I/O port, each 8-bit wide. Although the

Note:ColumnH4isnormallynotavailable

onatelephonekeypad.

HIGHGROUPTONES

LOWGROUP

TONES

H4=

1633

Hz

H3=

1477

Hz

H2=

1336

Hz

H1=

1209

Hz

L4=941Hz

L3=852Hz

L2=770Hz

L1=697Hz

D

C

B

A

#* 0

987

654

321

Figure1.3TonesassociatedwithkeysontelephoneDTMFkeypadmatrix

8/13/2019 DTMF12

8/48

8051 can have a maximum of 64K bytes of on-chip ROM, many manufacturers have put

only 4K bytes on the chip.

The 8051 became widely popular after Intel allowed other manufacturers to make

and market any flavor of the 8051 they please with the condition that they remain code-

compatible with the 8051. This has led to many versions of 8051 with different speeds and

amounts of on-chip ROM marketed by more than half a dozen manufacturers. It is

important to note that although there are different flavors of the 8051 in terms of speed and

amount of on-chip ROM, they are all compatible with the original 8051 as far as the

instructions are concerned. This means that if you write your program for one, it will run on

any one of them regardless of the manufacturer. The 8051 is the original member of the

8051 family. Intel refers to it as MCS-51. Although the 8051 is the most popular member of

the 8051 family, you will not see 8051 in the part number. This is because the 8051 is

available in different memory types, such as UV-EPROM, flash, and NV-RAM, all of which

have different part numbers.

1.3.2 AT89C51 from Atmel Corporation

This popular 8051 chip has on-chip ROM in the form of flash memory. This is ideal

for fast development since flash memory can be erased in seconds compared to the twenty

minutes or more needed for the 8751 (one of other members of the 8051 family). AT89C51

is used in the place of the 8751 to eliminate the waiting time needed to erase the chip and

thereby speed up the development time. To use the AT89C51 to develop a microcontroller-

based system requires a ROM burner that supports flash memory: however, a ROM eraser is

not needed. Notice that in flash memory you must erase the entire contents of ROM in

order to program it again. This erasing of flash is done by the PROM burner itself and this is

why a separate eraser is not needed. To eliminate the need for a PROM burner Atmel is

working on a version of the AT89C51 that can be programmed via the serial COM port of

an IBM PC.

2. OVERVIEW

8/13/2019 DTMF12

9/48

2.1 General block diagram of DTMF Remote Control System:

2.2 Working mechanism

The ring detector circuit detects ring signals that enable the unit to answer the call atright moment.

The ring detector circuit is nothing but an optocoupler circuit. When the call is done, the LED in the optocoupler glows and the phototransistor

sends a signal call of to the microcontroller.

SWITCHING

UNIT

RING

DETECTOR

REMOTE

TELEPHONE

TELEPHONECONNECTED

TOCONTROLLINGCIRCUIT

5V&12VREGULATED

POWERSUPPLY

ON/OFFCONTROL

CIRCUIT

TELEPHONE

INTERFACINGCIRCUIT

DTMF

DECODER

MONOSTA

BLE

MULTIVIBRATOR

89C51

MICR

OCONTROLLER

Figure2.1

8/13/2019 DTMF12

10/48

The microcontroller enables the switching unit to attend the call. (Electrically, it liftsthe call)

The integrated DTMF receiver and decoder decodes the tone dialing codes or tonedialing frequencies received via the telephone line in to a bit pattern of 4-bit BCD

code.

Depending on the signals given through the DTMF keypad or a telephone keypad,the microcontroller fetches the instructions from the inbuilt EPROM and controls

the devices connected through relays.

For example,Suppose that you are going to control a coffee machine (let it be the device number

one). Now to after the access code, if the key 1 is pressed twice, the device is switched ON,

and it is switched OFF by pressing 1 and then 0. This is fed to the microcontroller in the

form of an 8421 code.

3. DTMF UNIT

3.1 DTMF Tone Generator

They stand for dual tone multi frequency. DTMF is the generic communications

term for touch-tone. Touch-tone is a registered trademark of ATT; everyone in the

communication industry refers it as DTMF. Our Touch-tone phone is technically a DTMF

generator; it produces DTMF tones as we press the buttons.Many eons ago, the engineers at the Bell Lab figured out that the dial pulse system

was not the best for long distances, reliability, using over microwave systems and so on.

Their Research showed that you could use tones to represent the digits that the person was

dialing. You could have a separate tone for each digit, but there is always a chance that a

random sound will be on the same frequency and trip up the system. So, they reasoned, if

you have two tones to represent a digit, then a false signal is likely to occur. This is the basis

8/13/2019 DTMF12

11/48

for the Dual Tone in the DTMF. The basic details of the DTMF keypad matrix are already

discussed in chapter.1.

So when you press the digit 1 on your telephone you generate the tones 1209Hz &

597Hz. So if you press the digit 2 will now generate the tones 1336Hz & 697Hz.Sure, the

tone 697 Hz is the same but it takes two tones to make a digit and the telephone equipment

knows the difference.

3.2 8870 DTMF Receiver and Decoder

3.2.1 Features:

Complete DTMF receiver Low power consumption Internal gain setting amplifier Adjustable guard time Central office quality Power down mode Inhibit mode Backward compatible with 8870C/8870C-1

3.2.2 Applications:

Receiver system for British telecom

Repeater systems/Mobile radio Credit card systems Remote control Personal computers Telephone answering machine

3.2.3 Description:

The 8870D/8870D-1 is a complete DTMF receiver integrating both the band split

filter and digital decoder functions. The filter section uses switched capacitor techniques for

8/13/2019 DTMF12

12/48

high and low group filters; the decoder uses digital counting techniques to detect and decode

all 16 DTMF tone pairs into a 14 bit code. External component count is minimized by on

chip provision of a differential input amplifier, clock oscillator and latched three state bus

interfaces.

3.2.4 Functional Block Diagram:

Q4

Q3

Q2

Q1

TOALL

CHIP

CLOCKS

ZEROCROSSING

DETECTORS

VRef

BUFFER

INH

VRef

VSS

VDD

CHIP

BIAS

CH

IP

POW

ER

TOE

STD

EST

St/GT

OSC2

OSC1

ST

GT

STEERING

LO

GIC

CODE

CONVERTER

ANDLATCH

DIGITAL

DETECTION

ALGORITHM

DIAL

TONE

FILTER

LOWGROUP

FILTE

R

HIGHGROUP

FILTE

R

BIAS

CIRCUIT

FIGURE3

.1

8/13/2019 DTMF12

13/48

3.2.5 Functional Description:

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low

power consumption and high performance. Its architecture consists of a band split filter

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 band pass 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 smoothes 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 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) 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:

8/13/2019 DTMF12

14/48

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. Logic high on ESt causes Vc to raise as the

capacitor discharges. Provided signal VDD condition is maintained (ESt remains high) for

the validation period (tGTP), Vc reaches the threshold (VTSt) of the steering logic to

register the tone pair, latching its corresponding 4-bit code into the output latch. At this

point the GT output is activated and drives Vc to VDD. GT continues to drive high as long

as ESt remains high. Finally, after a short delay to allow the output latch to settle, the delayed

steering output flag (StD) goes high, signaling that a received tone pair has been registered.

The contents of the output latch are made available on the 4-bit output bus by raising the

three state control input (TOE) to logic high. The steering circuit works in reverse to

validate the interdigit pause between signals. Thus, as well as rejecting signals too short to be

considered valid, the receiver will tolerate signal interruptions (dropout) too short to be

considered a valid pause.

Digit TOE INH Q4 Q3 Q2 Q1

1 H X 0 0 0 1

2 H X 0 0 1 0

3 H X 0 0 1 1

4 H X 0 1 0 0

5 H X 0 1 0 1

6 H X 0 1 1 0

7 H X 0 1 1 1

8 H X 1 0 0 0

9 H X 1 0 0 1

0 H X 1 0 1 0

Figure 3.2 Steering circuit

8/13/2019 DTMF12

15/48

. H X 1 0 1 1

# H X 1 1 0 0

A H L 1 1 0 1

B H L 1 1 1 0

C H L 1 1 1 1

D H L 0 0 0 0

Table 3.1 Functional decode table

Guard Time Adjustment

In many situations not requiring selection of tone duration and interdigital pause, the

simple steering circuit is applicable. Component values are chosen according to the formula:

tREC=tDP+tGTP

tID=tDA+tGTA

The value of tDP is a device parameter and tREC is the minimum signal duration to

be recognized by the receiver. A value for C of 0.1 F is recommended for most

applications, leaving R to be selected by the designer. Different steering arrangements may

be used to select independently the guard times for tone present (tGTP) and tone absent

(tGTA). This may be necessary to meet system specifications, which place both, accept and

reject limits on both tone duration and interdigital pause. Guard time adjustment also allows

the designer to tailor system parameters such as talk off and noise immunity. Increasing

tREC improves talk-off performance since it reduces the probability that tones simulated by

speech will maintain signal condition long enough to be registered. Alternatively, a relatively

short tREC with a long tDO would be appropriate for extremely noisy environments where

fast acquisition time and immunity to tone drop-outs are required. The 8870 DTMF IC

consists of both the receiver and the decoder. The given frequency is decoded by means of a

filter section and a decoder section and converted to the corresponding 8421 code by the IC

to represent the key that has been pressed. This code acts as the input to the

microcontroller. The microcontroller accepts the 8421 code as input. It is programmed to

perform a specific operation for each possible key that may be pressed.

For example,

8/13/2019 DTMF12

16/48

Suppose that you are going to control a coffee machine (let it be the device number

one). Now to after the access code, if the key 1 is pressed twice, the device is switched ON,

and it is switched OFF by pressing 1 and then 0.

4. MASTER UNIT

4.1 Master Circuit of DTMF Remote Control System:

17

16

1

5 14

13

12

11

10

8

7

654321

4K7

4K7

4K7

4K7

4K7

4K7

4K7

R23

R22

R21

R20

R19

R18

R17

T3

R16

911

10

13

651284

1

3

21MR12

10V

4m7

C7

IC4

CD4047 RSTQQ

OSC

CX

RX

RCC

AST

-TRET

+T

AST

5V

4M7R15

100n

C8

D10

390R14

BC516

1M

2K7

R13

R11

RELAY

CIRCUIT

IC3ULN2003A12V

16

15

1413

1211

10

9 8

7654321

OUT7

OUT6

OUT5

OUT4

OUT3

OUT2

OUT1

IN7

IN6

IN5

IN4

IN3

IN2

IN1

M8870

IC2ST

/G

T

OE

ICICVREF

GS

IN-

IN+

OSC2

OSC1

Q4

Q3

Q2

Q1

STD

EST

D9

D8

3.579545MHz

X1

270KR36

100n

C18

R10

10K

10m10V

C4

5V

5V

5V

5V

5V

100n

5V

C11

47p

47p

C6

C5

X2

18

19

20

X2

X14

0 IC189C51

TXD

RXD

INT1

INT0

P1.7

P1.6

T1

T0

P1.5

P1.4

P1.3

P1.2

P1.1/T

2X

P1.0/T

2

RESET

15

14

13

12

11

109 87654321

EA/V

P

33

34

35

36

37

38

39

P0.6

P0.5

P0.4

P0.3

P0.2

P0.1

P0.0

8/13/2019 DTMF12

17/48

4.2 CIRCUIT OPERATION:

The heart of the circuit diagram is formed by an 89C51 micro controller. The

computer control section sits between a telephone interface circuit and a power switching

interface. The integrated DTMF decoder MV8870 decodes the tone dialing codes received

via telephone line.

The telephone line interface consists of two parts: one to detect the ring signals that

enables the unit to answer the call at the right moment, and another to receive and transmit

tones via the telephone lines

The ringing signal detector is relatively simple. A bridge rectifier, D3-D6, connected

to the telephone lines turns the ringing signal into a pulsating direct voltage, which is

smoothened by C3, and limited, to 15V with the aid of zener diode D7. The direct voltage

across D7 supplies the LED in optocoupler IC, with resistor R9 acting as current limiter.

During the ringing signal, the collector of the photo transistor in the optocoupler

(pin 8) is at ground potential. The microcontroller interrogates the state of the optocoupler

output signal via port line P1.7. To suppress error pulses, the low level at the optocoupler is

also used to trigger monostable multivibrator IC. The MMVs mono time is started by the

ringing signal, and supplies a logic high level to microcontroller pin INT0/P3.2 for about ten

seconds. This is the period available for transmitting codes to the switching unit. As long as

8/13/2019 DTMF12

18/48

the circuit has not lifted the receiver, i.e., as long as relay Re1 is not energized, the MMV is

triggered again via the RET connection.

The coupling with R7-C2 ensures that the ringing signal detector responds to

alternating voltage only. Any direct voltage levels that may exist between terminals a and b

are ignored.

When the microcontroller has counted the preprogrammed number of ringing

pulses, it responds by pulling output P1.6 logic high, which causes relay Re1 to be energized

via R6 and T1. This means that the switching unit lifts the receiver, i.e., answers the call.

This energizes the relay coil connected to the telephone lines. The current flowing through

this network is sufficiently large to maintain the connection. One end of the transformer

secondary winding is connected to the positive supply voltage via R1, while the other end is

connected to the ground via R2 and T2. This means that rectangular voltages generated by

the controller on line T0/P3.4 are coupled directly on to the telephone network lines. Two

zener diodes D1and D2 limit the voltage across the secondary winding to safe levels.

The received DTMF signals are capacitively coupled to the decoder. The external

components that enable the M8870 DTMF decoder to operate reliably are limited to four

resistors, a capacitor and a quartz crystal. The four decoder outputs, Q1 to Q4, supply a bit

pattern that corresponds to the received DTMF number, sign or letter. The structure of the

bit pattern is given in the table below. The 4-bit DTMF code is applied to the

microcontroller via port lines P1.0 to P1.3.

The microcontroller has its external address (EA) line tied to ground, and fetches

instructions from the inbuilt 128x8-bit internal RAM. The only two user programmable

parameters, the number of ringing signals and the access code are also stored in the internal

RAM. The output ports P0.0 to P0.6 are used to control relays through ULN2003A IC

(Relay driver IC) based on the keys pressed on the DTMF keypad. All the relays are

commoned to the 12v positive supply. The circuit diagram associated with relay connections

is shown in the figure.4.2.

RL1

12V

LOAD

N/O

N/C

8/13/2019 DTMF12

19/48

The power supply of the telephone controlled switch is conventional, and based on

fixed voltage regulator. The 12V and 5V supply voltages are used for the relay sections and

are derived from a mains transformer with secondary voltage of 12V. The corresponding

circuit diagram is shown in the figure below.

12V

1

2

3

230VAC

50Hz

Tr2

B1 -+

1000m

C25

5VIC7805

Figure 4.2 Relay circuit

8/13/2019 DTMF12

20/48

5. SOFTWARE CODING

5.1 Algorithm:

Step 1: Start

Step 2: Initialize data required

Step 3: If the data logic ready signal is high, go to step 4

Else go to step 3

Step 4: Read the keys equivalent of BCD code received

Step 5: If it is 11, go to step 6

Else if it is 10, go to step 7












Figure 4.3 Power supply circuit

8/13/2019 DTMF12

21/48




Else if it is *1, go to step 22

Else if it is *2, go to step 24

Else, go to step 25

Step 6: Switch ON device number 1

Step 7: Switch OFF device number 1













Step 20: Switch ON all devices

Step 21: Switch OFF all devices

Step 22: If it is #, go to step 23

Else, read and store the data

Step 23: Disable the personal access code

Step 24: Read and store the data

Step 25: If it is n2 (1

8/13/2019 DTMF12

22/48

5.2 Flow chart:

A

START

INITIALIZEREQUIREDDATA

CHECK

LOGICREADY

READTHECORRESPONDINGKEYS

OFTHEBCDCODERECEIVED

SWITCHON

DEVICENO.1

SWITCHOFF

DEVICENO.1

SWITCHON

DEVICENO.2

SWITCHON

DEVICENO.3

SWITCHOFF

DEVICENO.3

SWITCHOFF

DEVICENO.2

CHECK

IF

11OR10

CHECK

IF

21OR20

CHECK

IF

31OR30

LOW

HIGH

1011

2021

NO

NO

NO

3031

A

SWITCHOFF

DEVICENO.4

SWITCHON

DEVICENO.4

SWITCHONDEVICENO.5

SWITCHOFFDEVICENO.5

SWITCHOFF

DEVICENO.6

SWITCHON

DEVICENO.6

CHECK

IF

41OR40

CHECK

IF

51OR50

CHECK

IF

61OR60

CHECK

IF

71OR70

NO

NO

NO

71 70

61 60

50

40

51

41

B

SWITCHOFF

ALLDEVICES

SWITCHON

ALLDEVICES

CHECKIF

81OR80

8081

NO

8/13/2019 DTMF12

23/48

5.3 Assembly Language Program:

RAM0 DATA 30HRAM1 DATA 31H

RAM2 DATA 32HRAM3 DATA 33HRAM4 DATA 34HRAM5 DATA 35HRAM6 DATA 36HRAM7 DATA 37HRAM8 DATA 38HRAM9 DATA 39HRAMA DATA 3AH

ORG 00HLJMP J1LCALL SUB1LJMP J2

ORG 0009HSUB1: CLR EA

RETIORG 0100H

J1:MOV A,#0FFH ; MOV DPTR,#8000HMOV P0,A ; CLR A

8/13/2019 DTMF12

24/48

;MOVX @DPTR,ACLR AMOV RAM1,A

INC AMOV RAM2,AINC AMOV RAM3,AINC AMOV RAM4,AINC AMOV RAM5,AINC AMOV RAM6,AINC A

MOV RAM7,AMOV RAM8,#0CHMOV RAM0,#06H

J2: MOV SP,#07HLCALL SUB2LCALL SUB3

J3: LCALL SUB4JB P1.7,J3

J4: JB P1.7,J4LCALL SUB3JB P1.7,J4

JNB P1.7,$LCALL SUB3DJNZ R0,J4SETB P1.6LCALL SUB3LCALL SUB4LCALL SUB5LCALL SUB3LCALL SUB3LCALL SUB3LCALL SUB3LCALL SUB3LCALL SUB4MOV A,#0CHCJNE A,RAM2,J5LCALL SUB5LJMP J6

J5: LCALL SUB6CJNE A,RAM2,J7MOV A,#0CHCJNE A,RAM3,J8LCALL SUB5LJMP J6

8/13/2019 DTMF12

25/48

J8: LCALL SUB6CJNE A,RAM3,J7MOV A,#0CH

CJNE A,RAM4,J9LCALL SUB5LJMP J6


J7: LCALL SUB7LJMP J2


J11: LCALL SUB6CJNE A,RAM6,J7MOV A,#0CHCJNE A,RAM7,J12LCALL SUB5

LJMP J6J12: LCALL SUB6CJNE A,RAM7,J7MOV A,#0CHCJNE A,RAM8,J13LCALL SUB5LJMP J6


J14: LCALL SUB6CJNE A,RAM9,J7MOV A,#0CHCJNE A,RAMA,J7LCALL SUB5LJMP J6

J6: LCALL SUB6CJNE A,#01,J50LCALL SUB6CJNE A,#0AH,J51

8/13/2019 DTMF12

26/48

MOV A,RAM1ANL A,#0FEHMOV RAM1,A

LCALL SUB8LCALL SUB7LJMP J6

J51: CJNE A,#01,J15MOV A,RAM1ORL A,#01MOV RAM1,ALCALL SUB8LCALL SUB5LJMP J6

J15: CJNE A,#02,J52

MOV A,RAM1ANL A,#01JNZ J53LCALL SUB7LJMP J6


J52: LJMP J2J50: CJNE A,#02,J16

LCALL SUB6CJNE A,#0AH,J17

MOV A,RAM1ANL A,#0FDHMOV RAM1,ALCALL SUB8LCALL SUB7LJMP J6

J17: CJNE A,#01, J18MOV A,RAM1ORL A,#02MOV RAM1,ALCALL SUB8LCALL SUB5LJMP J6

J18: CJNE A,#02,J19MOV A,RAM1ANL A,#02JNZ J54LCALL SUB7LJMP J6


J19: LJMP J2J16: CJNE A,#03,J20

8/13/2019 DTMF12

27/48

8/13/2019 DTMF12

28/48

8/13/2019 DTMF12

29/48


J34: LJMP J2

J31: CJNE A,#07,J35LCALL SUB6CJNE A,#0AH,J36MOV A,RAM1ANL A,#0BFHMOV RAM1,ALCALL SUB8LCALL SUB7LJMP J6

J36: CJNE A,#01,J37MOV A,RAM1

ORL A,#40HMOV RAM1,ALCALL SUB8LCALL SUB5LJMP J6

J37: CJNE A,#02,J38MOV A,RAM1ANL A,#40HJNZ J60LCALL SUB7LJMP J6

J60: LCALL SUB5LJMP J6J38: LJMP J2J35: CJNE A,#08,J39

LCALL SUB6CJNE A,#0AH,J40MOV A,#00MOV RAM1,ALCALL SUB8LCALL SUB7LJMP J6

J40: CJNE A,#01,J39MOV A,RAM1ORL A,#01MOV RAM1,ALCALL SUB8LCALL SUB3MOV A,RAM1ORL A,#02MOV RAM1,ALCALL SUB8LCALL SUB3MOV A,RAM1

8/13/2019 DTMF12

30/48

ORL A,#04MOV RAM1,ALCALL SUB8

LCALL SUB3MOV A,RAM1ORL A,#08MOV RAM1,ALCALL SUB8LCALL SUB3MOV A,RAM1ORL A,#10HMOV RAM1,ALCALL SUB8LCALL SUB3

MOV A,RAM1ORL A,#20HMOV RAM1,ALCALL SUB8LCALL SUB3MOV A,RAM1ORL A,#40HMOV RAM1,ALCALL SUB8LCALL SUB5LCALL SUB4

LJMP J6J39: CJNE A,#0BH,J42LCALL SUB6CJNE A,#01,J44LCALL SUB5LCALL SUB11LJMP J6

J44: CJNE A,#02,J43LCALL SUB5LCALL SUB12LJMP J6

J43: CJNE A,#03,J42LCALL SUB13LJMP J6

J42: LCALL SUB7LJMP J2ORG 0466H

SUB4:MOV IEN0,#00SETB P1.5CLR P1.5MOV IEN0,#81HRET

8/13/2019 DTMF12

31/48

ORG 0471H

SUB3:

MOV R6,#0B1HJ62: MOV R7,#0FFH

DJNZ R7,$DJNZ R6,J62RET

ORG 047AHSUB2:

MOV IEN0,#00MOV P1,#0BFHMOV R0,RAM0RET

ORG 0483HSUB9:

MOV R5,#03J64: MOV R6,#0FFHJ63: MOV R7,#0FFH

SETB P3.4DJNZ R7,$MOV R7,#0FFHCLR P3.4DJNZ R7,$DJNZ R6,J63

DJNZ R5,J64RETORG 0498H

SUB8:CPL AMOV P0,A ;MOV DPTR,#8000H

;MOVX @DPTR,ARET

ORG 049DHSUB6:

JNB P1.4,$MOV A,P1ANL A,#0FHJB P1.4,$LCALL SUB4RET

ORG 04ABH

ORG 04BCHSUB7:

LCALL SUB9LCALL SUB9

8/13/2019 DTMF12

32/48

RETORG 04C3H

SUB11:

MOV R1,#41HJ66: LCALL SUB6

LCALL SUB10CJNE A,#0CH,J65MOV @R1,A

J67: MOV RAM2,41HMOV RAM3,42HMOV RAM4,43HMOV RAM5,44HMOV RAM6,45HMOV RAM7,46H

MOV RAM8,47HMOV RAM9,48HMOV RAMA,49HLCALL SUB5RET

J65:MOV @R1,AINC R1CJNE R1,#49H,J66MOV @R1,#0CHLJMP J67

ORG 04F8HSUB12:

LCALL SUB6CJNE A,#01,J68LJMP J69

J68: CJNE A,#02,J70LJMP J69

J70: CJNE A,#0AH,J71CLR A

J69: RLC ARLC ARLC ARLC AMOV 41H,ALCALL SUB10LCALL SUB6CJNE A,#01,J72LJMP J73



8/13/2019 DTMF12

33/48


J76: CJNE A,#05,J77

LJMP J73J77: CJNE A,#06,J78



LJMP J73J80: CJNE A,#09,J71J73: ADD A,41H

MOV RAM0,ALCALL SUB5

RETJ71: LCALL SUB7

RETSUB14: MOV A,#05J82: LCALL SUB3

DEC AJNZ J82RET

ORG 055FHSUB13:

LCALL SUB6J83: MOV 41H,ALCALL SUB10LCALL SUB14MOV A,41HDEC AJNZ J83RET

END

8/13/2019 DTMF12

34/48

6. CONCLUSION

This project has primarily dealt with the control of home appliances using a

telephone line. The choice of DTMF technology (which is used by the DTMF telephone

line) over conventional RF technology has resulted in our model possessing superior features

in the following ways

Significantly lower cost. Use of a universally accepted technology. No imposition of limit on the distance. Relatively free from interference problems.

We have used this telephone line method to place a call to another phone, which is

connected to the main controlling circuit. When picked up, any key pressed generates a

complex frequency or touch-tone. This is then decoded by means of a DTMF circuit to give

the key pressed. This is given to the microcontroller, which then gives instructions to

perform the task required. Thus, we see the model has been built using components, which

are not only widely available, but also relatively cheap. A noteworthy point about this project

is its wide and varied applications. As this process of controlling things using telephone linecould be used not only in industrial applications, but also domestic ones, this project has

proved its ability to be used in a variety of applications.

6.1 Future Enhancement

Its utility is further enhanced by using devices such as LCDs etc mounted on the

main circuit. The areas in which this model finds applications includes Caller IDs, Answering

Machines.

6.2 Applications

8/13/2019 DTMF12

35/48

One of the primary applications of this project is the process of operation is very simple,

so that every person could operate it very easily.

Another important application of this is its wide use in industrial area. Not only inindustrial area, it can also be used widely in domestic applications.

The applications of this project also extend in making caller IDs, AnsweringMachines, etc.

Thus, it is seen that this project has not only proved itself superior in terms of

effectiveness and cost, but also has utility in innumerable applications.

Appendix 1

Microcontroller: AT89C51

Features

Compatible with MCS-51 Products 4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase Cycles Fully Static Operation: 0 Hz to 24 MHz Three-level Program Memory Lock 128 x 8-bit Internal RAM 32 Programmable I/O Lines Two 16-bit Timer/Counters Six Interrupt Sources Programmable Serial Channel

8/13/2019 DTMF12

36/48

Low-power Idle and Power-down Modes

Description

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with

4K bytes of Flash programmable and erasable read only memory (PEROM). The device is

manufactured using Atmels high-density nonvolatile memory technology and is compatible

with the industry-standard MCS-51 instruction set and pinout. 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

AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective

solution to many embedded control applications.

Pin Diagram

8/13/2019 DTMF12

37/48

8/13/2019 DTMF12

38/48

The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes

of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt

architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the

AT89C51 is designed with static logic for operation down to zero frequency and supports

8/13/2019 DTMF12

39/48

8/13/2019 DTMF12

40/48

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 use 16-bit addresses (MOVX @ DPTR). In this

application, it 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 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 listed below:

Port 3 also receives some control signals for Flash programming and verification.

RST

8/13/2019 DTMF12

41/48

Reset input. A high on this pin for two machine cycles while the oscillator is running

resets the device.

ALE/PROG

Address Latch Enable 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 a constant 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 microcontroller is in external execution

mode.

PSEN

Program Store Enable is the read strobe to external program memory. When the

AT89C51 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 programming, for parts that require

12-volt VPP.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating

circuit.

8/13/2019 DTMF12

42/48

XTAL2

Output from the inverting oscillator amplifier.

Appendix 2

CD4047BC

Low Power Monostable/Astable Multivibrator

General Description

The CD4047B is capable of operating in either the monostable or astable mode. It

requires an external capacitor (between pins 1 and 3) and an external resistor (between pins 2

and 3) to determine the output pulse width

in the monostable mode, and the output frequency in the astable mode. Astable operation is

enabled by a high level on the astable input or low level on the astable input. The output

frequency (at 50% duty cycle) at Q and Q outputs is determined by the timing components.

A frequency twice that of

Q is available at the Oscillator Output; a 50% duty cycle is not guaranteed.

Monostable operation is obtained when the device is triggered by LOW-to-HIGH transition

at trigger input or HIGH-to-LOW transition at

trigger input. The device can be

retriggered by applying a simultaneous LOW-to-HIGH transition to both the trigger and

retrigger inputs. A high level on Reset input resets the outputs Q to LOW, Q to high.

Monostable Multivibrator Features

Positive- or negative-edge trigger Output pulse width independent of trigger pulse duration Retriggerable option for pulse width expansion Long pulse widths possible using small RC components by means of external

counter provision

Fast recovery time essentially independent of pulse width Pulse-width accuracy maintained at duty cycles approaching 100%

Astable Multivibrator Features

Free-running or gettable operating modes

8/13/2019 DTMF12

43/48

50% duty cycle Oscillator output available Good astable frequency stability typical+/-2% 0.03%/`C @ 100 kHz

frequency+/-0.5% 0.015%/`C @ 10 kHz deviation (circuits trimmed

to frequency VDD=10V +/-10%)

Features

Wide supply voltage range: 3.0V to 15V High noise immunity: 0.45 VDD (typ.)

Low power TTL compatibility: Fan out of 2 driving 74L or 1 driving 74LS

Special Features

Low power consumption: special CMOS oscillator configuration Monostable (one-shot) or astable (free-running) operation True and complemented buffered outputs Only one external R and C required

Applications

Frequency discriminators Timing circuits Time-delay applications Envelope detection Frequency multiplication Frequency division

Pin Diagram CD4047

8/13/2019 DTMF12

44/48

Functional Block Diagram

8/13/2019 DTMF12

45/48

Appendix 3

ULN2003A-ULN2004A

ULN2001A-ULN2002A

SEVEN DARLINGTON ARRAYS

Seven darlingtons per package Output current 500mA per driver (600mA peak) Output voltage 50V Integrated suppression diodes for inductive loads Outputs can be paralleled for higher current TTL/CMOS/PMOS/DTL compatible inputs Inputs pinned opposite outputs to simplify layout

8/13/2019 DTMF12

46/48

DESCRIPTION

The ULN2001A, ULN2002A, ULN2003 and ULN2004A are high voltage, high

current Darlington arrays each containing seven open collector Darlington pairs with

common emitters. Each channel rated at 500mA and can withstand peak currents of 600mA.

Suppression diodes are included for inductive load driving and the inputs are pinned

opposite the outputs to simplify board layout.

The four versions interface to all common logic families:

These versatile devices are useful for driving a wide range of loads including

solenoids, relays DC motors; LED displays filament lamps, thermal printheads and high

power buffers. The ULN2001A/2002A/2003A and 2004A are supplied in 16 pin plastic

DIP packages with a copper lead frame to reduce thermal resistance. They are available also

in small outline package (SO-16) as ULN2001D/2002D/2003D/2004D.

Pin Connection

8/13/2019 DTMF12

47/48

8/13/2019 DTMF12

48/48

REFERENCES

Books

1. Muhammad Ali Mazidi & Janice Gillispie Mazidi (2005), The 8051 MicrocontrollerAnd Embedded Systems, Pearson Education.

2. Kirk Zurell (2000), C Programming For Embedded systems, CMP Books, Edition2.

Periodicals

1. Electronics For You2. Elector India Electronics

Websites

1. http://www.eletronicsforu.com2. http://www.programmers heaven.com3. http://www.alldatasheets.com4. http://www.electorindiaelectronics.com

DTMF12

Documents

Transcript of DTMF12