Abstract:
This Project is used to control our household electrical devices from any where through the cell phone. The circuit consists of a DTMF tone detector and a powerful 8 bit Microcontroller AT89S52. The microcontroller controls all the system. In this project we control total six devices.

The Microcontroller senses the DTMF signal through the DTMF decoder IC MT8870 and it switch on/off the corresponding devices according to the user need. The circuit has an inbuilt phone ring sensor circuit and the system will take over the phone control if it was not taken manually.Press the corresponding numbers to turn on/off the devices, for ex: press 1 to turn on/off device 1, press 0 to switch off all devices, press 9 to switch on all devices, press 8 to disconnect the telephone.

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INTRODUCTION-:
This Project is used to control our household electrical devices from anywhere through the cell phone. The circuit consists of a DTMF tone detector and a powerful 8 bit Microcontroller AT89S52. The microcontroller controls all the system. In this project we control total six devices.
The Microcontroller senses the DTMF signal through the DTMF decoder IC MT8870 and it switch on/off the corresponding devices according to the user need. The circuit has an inbuilt phone ring sensor circuit and the system will take over the phone control if it was not taken manually. Press the corresponding numbers to turn on/off the devices, for ex: press 1 to turn on/off device 1, press 0 to switch off all devices, press 9 to switch on all devices, press 8 to disconnect the telephone
A BRIEF INTRODUCTION TO 8051
MICROCONTROLLER-:
When we have to learn about a new computer we have to familiarize about the machine capability we are using, and we can do it by studying the internal hardware design (devices architecture), and also to know about the size, number and the size of the registers.
A microcontroller is a single chip that contains the processor (the CPU), non-volatile memory for the program (ROM or flash), volatile memory for input and output (RAM), a clock and an I/O control unit. Also called a "computer on a chip," billions of microcontroller units (MCUs) are embedded each year in a myriad of products from toys to appliances to automobiles. For example, a single vehicle can use 70 or more microcontrollers. The following picture describes a general block diagram of microcontroller.
AT89S52: The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory pro-grammer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller, which provides a highly flexible and cost-effective solution to many, embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation 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 con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt