HOME AUTOMATION CONTROL SYSTEM USING DTMF TELEPHONE LINE

INTRODUCTION

INTRODUCTION OF THE PROJECT

How this project is different from other home automation control system?

Controlling device using switches are common. From a few decades controlling devices using remote control switches like infrared remote control switch, wireless remote control switches, light activated switches are becoming popular. But these technologies have their own limitations. Laser beams are harmful to mankind.

Some technologies like IR remote control are used for short distance applications. In such case if we have system which does not require any radiations or which is not harmful, long remote control switch!! Yes here is the solution. Here I am introducing such a system which does not require any radiations, any laser beam which has no limitation of range, I mean it can be used from any distance from meters to thousands kilometers using a simple telephone line or mobile phone.

Here I am using a telephone as a media, which serves main part of this system, by using home phone as a local phone and another phone, either landline or mobile phone as a remote phone.

The “Home Automation Control System Using DTMF Telephone Line” project is a secure DTMF control system for intelligent houses.

With this implemented system, it is possible to safely control electricity operated domestic devices.

FEATURES

1. We can control up to 8 devices. It may be any electric or electronic appliances or devices with simple to heavy appliance. Each device is given a unique code.
2. It makes accurate switching, any false switching of device are not done so there is no risk for false switching.
3. Our local phone can be used for normal use by using a DPDT switch. So we need not use a separate telephone line for this device controlling.
4. To perform any operations through remote phone line, the user needs to dial to the local telephone then the respective code of the device is dialed.
5. This circuit not require any complex IC, so any one with little knowledge of electronics can construct this circuit, because it does not need any programmable IC’s or programming.
6. This system detects the ringing signal from your exchange with the help of ring detector and automatically switches ON.
7. This device saves our money. This circuit switches OFF after a time of 60 seconds.
8. Before changing the state of the device we can confirm the present status of the device.
9. This circuit gives an acknowledgement tone after switching ON the devices to confirm the status of the device.
10. We can control devices from any local telephone. It can also be controlled by PCO.

TAKING A TOUR OF PROJECT

This system uses Dual Tone Multi Frequency (DTMF) technology of our telephone set. Every telephone set will have this facility. We have two type of dialing facilities in our telephone system (1)pulse dialing mode (2) tone dialing mode. Here this system works on tone dialing mode. The DTMF mode is shortly called as tone dialing mode.
This system is divided into two sections.
1: Remote section
2: Local control section.

What is DTMF?

When you press a button in the telephone set keypad, a connection is made that generates a resultant signal of two tones at the same time.
This two tones are taken from a row frequency and a column frequency. The resultant frequency signal is called a “Dual Tone Multiple Frequency “.
These tones are identical and unique.
A DTMF signal is the algebraic sum of two different audio frequencies, and can be expressed as follows:
f(t) = A0sin(2*?*fa*t)+B0sin(2*?*fb*t)+…--- > (1)
Where fa and fb are two different audio frequencies with A and B as their peak amplitude and f as the resultant DTMF signal.
fa belongs to the low frequency group and fb belongs to the high frequency group.
Each of the low and high frequency groups comprise four frequencies from the various keys present on the telephone keypad; two different frequencies, one from the high frequency group and another from the low frequency group are used to produce a DTMF signal to represent the pressed key.
The amplitudes of the two sine waves should be such that

(0.7<(A\B)<0.9)v> (2)

The frequencies are chooses such that they are not the harmonics of each other. The frequencies associated with various keys on the keypad are shown in figure(A).
When you send this DTMF signals to the telephone exchange through cables, the servers in the telephone exchange identifies these signals and makes the connection to the person you are calling.

CIRCUIT DIAGRAM

RELAY DRIVER CIRCUIT

DESCRIPTION

The brain of the switcher is the Atmel AT89xxx micro controller U3. Incoming ring is detected via C10, D9, R16 and the opto- coupler U6 and connected to pin 12 of the micro controller.

The incoming call is answered by connecting the circuit based around Q1 and R4 (an electronic holding coil) to the line. One output from micro controller (pin 13) is used to output a 325Hz software generated tone into the telephone line via the Q2, This tone is used to signal the user when commands have been completed or of any command errors.

The micro controller examines incoming signals on port 1 (P1.0 - P1.4) and controls the outputs over port 0 (P0.0 - P0.7).

Connection to the telephone network is via RJ11 connector K2. Socket K3 is connected in parallel with socket K2 and allows a telephone to be connected at the same time as the circuit. A voltage-dependent resistor (visitor) is connected across these two sockets, which provides protection against voltages in excess of 130 V.

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 Atmel’s high-density nonvolatile memory technology and is compatible with the industry- standard MCS-51 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 AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications.

DTMF DECODER INTERFACE

DTMF detection and decoding is provided by U5. This chip, an 8870, is a complete DTMF receiver, which is able to detect and decode all 16 DTMF tone pairs into a 4-bit code. When a valid DTMF digit is detected the 4-bit code is placed on pins 11-14 and a 'data available' output, pin 15, is set to logic high. It is connected to the telephone line via C2 and R9 and R14 a hexadecimal value corresponding to the two tones at its outputs Q1 to Q4.

These outputs are latched and so are only valid when the control output STD is high. For its operation the integrated circuit requires a base of times, generated in this case by the quartz crystal of 3.579545MHz. This crystal is very common in the market since he is the employee for the systems of color of the TV equipment