Synopsis

Title: CELLPHONE OPERATED HOME AUTOMATION SYSTEM.

Introduction Dial your number using DTMF phone or Cell phone from anywhere in the world and remotely turn on/off any of the 8 relays. 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. This interface uses the popular MT8870 DTMF decoder IC along with AT89S51 Microcontroller. Features• Outputs - Relays x 8• Fully microcontroller based interface using AT89S51.• Auto line pick up.• On Board flash EEPROM that stores system Parameters and password and relay status (no require battery back up)• User settable password for security.• 16x2 Line LCD module to display Status and Error Message.• Acknowledgement tone out put for the user.

PROJECT CYCLE

1. Specification of the Project.

2. PCB Layout.

3. Device Test.

4. Code Implementation.

5. Program Test.

6. Pilot Run.

7. Documentation.

Block Diagram

DescriptionThe block diagram is shown in figure1. The brain of the circuit is the ATMEL AT89S51 microcontroller. The micro controller examines incoming signals through DTMF decoder and controls the outputs by relays. The audio output from the cell phone is connected to the input of DTMF decoder.

The incoming call is answered by the cell phone.

DTMF detection and decoding is provided by DTMF decoder block. An IC MT 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 available at the output pins and a VALID SIGNAL output, is set to logic high. For its operation the integrated circuit requires a clock signal, generated in this case by the quartz crystal of 3.579545MHz.

A two-wire serial EEPROM (AT24C02) is used in the project to retain the password, the relay status and the number of rings to which the system should respond. Data stored remains in the memory even after power failure, as the memory ensures reading of the latest saved settings by the micro controller. This 12C bus compatible- 2048-bit (2-kbit) EEPROM is organized as 256x8 bits. It can retain data for more than ten years. Using just two lines (SCL and SDA) of the memory, the microcontroller can read and write the data corresponding to the data required to be stored.

A 16x2 Line LCD module is used to display the Status and Error Messages.

24C02 SERIAL EEPROM

RELAY DRIVERULN2803

CELL-PHONE

ATMEL 89C51

DTMF ENCODER

RELAY

REGULATED POWER SUPPLY

Two supply voltages are required for the circuit which is derived from main 230V by step down transformer, bridge rectifier, filter and regulators. A 7805 is used which is fixed voltage 5V Regulator for 5V supply. The unregulated voltage of approximately 12 V is required for the relay driving circuit.

ATMEL AT89S51 is used in the project. This particular microcontroller is chosen because following features.

1. 4K Bytes of In-System programmable flash memory.2. Compatible with MCS®-51 Products3. 4.0V to 5.5V Operating Range 4. Fully Static Operation: 0 Hz to 33 MHz 5. 128 x 8-bit Internal RAM 6. 32 Programmable I/O Lines7. Low cost.

Software

1. KEIL Uv2 IDE

2. ATMEL PROGRAMMER.

3. EMBEDDED C PROGRAMMING LANGUAGE.

Tools for schematic design1. CAPTURE CIS (ORCAD)

Hardware

1. ATMEL 89C51 controller,

2. AT 24C02 SERIAL EEPROM,

3. DTMF ENCODER,

4. RELAY DRIVER ULN2803,

5. LCD,

6. PCB for microcontroller unit, Reset switches, resistors etc,

7. RELAY,

8. Crystal 11.0592 MHz

Working principleThe HOME AUTOMATION SYSTEM is connected to cell phone using enhancement. The caller has to dial the cell phone number. After two or three rings the cell phone picks up call.

Then he has to enter the six-digit password. After the successfully entering of password the relay will be activated. 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.

Applications• Home automation and device control system• Telephone answering machine• DTMF remote controlling by cell phone or telephone