HOME AUTOMATION CONTROL SYSTEM USING DTMF

INDEX

Introduction What is DTMF ? Block Diagram System Working Circuit Diagram ICs Used Applications Merits & Demerits Features of TCS Future Expansion

INTRODUCTION

One can access this unit even when he/she is not present at the place where the system is installed.

Any (DTMF) telephone set or hand-held tone dialer may be used to send commands to the switching unit.

The switching unit is capable of controlling mains, powered loads with the aid of commands received via a telephone.

WHAT IS DTMF ?

Dual tone multiple frequency signaling (DTMF).

Multiple-frequency signaling consists of a combination of two tones with frequencies within the speech band.

Each combination of two frequencies representing a single digit.

The tones are in two groups : 1 Low Band 2 High Band

DTMF(DUAL TONE MULTIPLE FREQUENCY

SIGNALING)  Low High 1209 HZ 1336 HZ 1447 HZ

1633 HZ 697 HZ 1 2 3

A 770 HZ 4 5 6

B 852 HZ 7 8 9

C 941 HZ * 0 #

D

BLOCK DIAGRAM

SYSTEM WORKING

Dial your number using DTMF phone or Cell phone from anywhere in the world.

The MCU on the interface senses Telephone ring, Automatic telephone pick up, and line hang up, displays information on a 16x2 LCD module and controls the relay switching.

After a six rings the circuit lifts the receiver and sends an acknowledgement tone to signal to the caller that a six-digit password number is to be entered.

Enter the password.

When the password has been incorrectly entered four times in a row, the interface an error sound is produced and the receiver replaced on-hook this function thwarts any attempt by 'hackers' to quickly try a large number of codes in a sequence.

If password is correct enter in to the main menu . Main menu : Enter Command * < 1 – 8 > * - operate one of the four relays 1 to 8.

# < 1 – 8 > # - release one of the four relays 1 to 8.

123 – Read EPROM

456 – Change password

789 – Read relay status

* 0 # - Line disconnected

CIRCUIT DIAGRAM

Microcontroller interface

EEPROM interface

LCD interface

Regulated power supply

DTMF decorder interface

Ring detector

Acknowledgement tone output

RELAY DRIVER CIRCUIT

MICROCONTROLLER UNIT WORKS

To count the pre-programmed number of ringing signals.

To enable the high value resistance after counting the pulses.

To accept the decoded tones send by the tone decoder.

To operate the corresponding relays according to the signals.

ICS USED

AT89CXXX Microcontroller AT89C51 is a low-power, high-performance CMOS 8-bit

microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM).

LM 7805

Used to make the stable voltage of +5v for Microcontroller .

MT 8870 (DTMF DECORDER)

Complete DTMF receiver integrating both the band split filter and digital decoder functions.

Decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code.

MC T2E/4N35 (RING DETECTOR)

• It is used for ring detection .

• MCT2E series opt isolators consist of a gallium arsenide infrared emitting Diode driving a silicon photo transistor in a 6-pin dual in line package.

FLASH EEPROM – AT24C04

• AT24C04 are 4K bit electrically erasable programmable memories , Organize as 2 blocks of 256 * 8 bits.• They are manufactured in SGS-THOMSON’s Hi- Endurance Advanced CMOS technology .

LCD MODULE (16X2 LINE LCD)

SPDT RELAY – 12V

• It is used for switching (Turn ON/OFF) the device connected to it.

APPLICATIONS

Wide range of applications in various fields Household applications Industrial applications Office applications Institutional applications Telephone answering machine Interactive voice response system(IVRS)

MERITS & DEMERITS

No distance limitation. Instant switching without

any delay. Use less components and

power consumption is low.

Its cost is very less. It cannot be misused

unless any other person knows the code.

The unit cannot be accessed when the phone is dead.

It is only used on phones having DTMF dialing facilities.

The wiring becomes complex and costly.

FEATURES OF TCS

Easy availability : The components is used in the circuit are easily available in the market.

Flexibility : micro-controller offers lot of flexibility to the programmer for the programming purpose.

Compatibility : This switching unit is compatible with any kind of telephone set.

Versatileness : you can access and even connect desired no. of loads to it.

Longer period of service

Less experience : The PCB uses circuits that are very cheap. They are easily accessible as their voltage & power requirement is less.

Compactness : The unit is much more compact as the PCB is reduced to almost one fourth of the original PCB.

FUTURE EXPANSION

Increasing no. of channels: This circuit provides a facility for 8 channels. So we can

individually access each appliance to one channel.

If this is not desired then by the use of multiplexers and modification in the software and using the remaining ports we increase the no. of channels.