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INTRODUCTION
In this project, a system is designed and created which uses Dual Tone Multi Frequency (DTMF) technology of our mobile phone. Every mobile phone will have this facility. Long distance computer communication has become a challenge of the present day technology. Recently these computer communication networks are also termed as information networks. Presently there are many information services for information exchange like Telex, Electronics mail, Video teleconferencing, Facsimile transmission (FAX), which are quit efficient but expensive too. But there could be a situation where the terminal down load or upload few lines or files or say information, may be “OFF” from the mains. Thus all the technologies are failed. And this is where the project “Mobile Controlled Devices” comes into picture. To establish an interactive page link with such a terminal, the mains must be “ON”. To materialize such a system, it requires some circuitry which would receive commands on telephone line and can switch mains load “ON” or “OFF”. The two major parts of the system are the hardware configuration and device control logic. This project is to eliminate the problem by using such a circuitry, which can switch the remote terminal ON/OFF without anybody being present at the remote location. This aim is achieved by using Mobile Control Devices.
1.1 Overview of the project
Conventionally, wireless controlled devices use RF circuits, which have the drawbacks of limited working range, limited frequency range, limited features and limited control options. To overcome all these limitations, this device is designed to operate through a mobile phone, there by it can be controlled any where from the world. It provides the advantages of device control, un-limited working range depending up on the coverage area of tele-communications network, no interference with other signals, and more control options. Generally from any mobile or any land line phone 12 different DTMF codes can be produced by activating the different keys of mobile keypad, so 12 different control options can be adopted in the device.
Generally for this purpose cordless phones (mobile phone) are best suited, it is the primary function of the device to carry the mobile over its chassis, there by the device can receive the command signals through this mobile. According to the control signals received from another mobile at remote end, the switching of devices can be controlled by decoding the DTMF signals received by the cordless phone. The operator controls it using the handset of the cordless phone.
The DTMF decoder circuit is designed with 8870 chips, this is a complete DTMF receiver integrating both the band split filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit code. External component count is minimized by on chip provision of a differential input amplifier, clock oscillator and latched three-state bus interface. The main controlling technique using this integrated DTMF IC is that it is having all DTMF Receiver Features like it has low power consumption, adjustable guard time, inhibit mode. It is widely used in Telephone answering machine; the MT8870D is a complete DTMF receiver integrating both the band split filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by on chip provision of a differential input amplifier, clock oscillator and latched three-state bus interface.
The prime use of microcontroller is to acquire data from DTMF decoder, and according to that it is the main function of the controller to control devices. Initially the process begins from mobile phone, depending up on the control signals in the form of DTMF code transmitted by the mobile or land line, the receiving mobile produces corresponding DTMF code. The output of the mobile is amplified to increase the signal strength and it is fed to DTMF signal decoder chip, which generates corresponding binary code at four outputs. This binary code differs depending up on the low frequencies produced by the exchange, whenever any key of calling mobile is operated, two low frequencies are produced and corresponding to this a particular binary code is produced by the DTMF chip. The output of the DTMF chip is fed to microcontroller. Here the microcontroller is playing major roll, hence it can be called as heart of the project work. There by the following is the brief introduction about the 89C52 microcontroller.
1.2 Requirements of Project
• MICRO CONTROLLER (89S52)
• DTMF 8870
• RELAY DRIVER
• RELAYS
• BULBS
• MOBILE
1.3 Criteria for Choosing 89S52 Microcontroller
A digital computer typically consists of three major components: the Central Processing Unit (CPU), program and data memory, and an Input/Output (I/O) system. The CPU controls the flow of information among the components of the computer. It also processes the data by performing digital operations. Most of the processing is done in the Arithmetic-Logic Unit (ALU) within the CPU. When the CPU of a computer is built on a single printed circuit board, the computer is called a minicomputer. A microprocessor is a CPU that is compacted into a single-chip semiconductor device. Microprocessors are general-purpose devices, suitable for many applications. A computer built around a microprocessor is called a microcomputer. The choice of I/O and memory devices of a microcomputer depends on the specific application. For example, most personal computers contain a keyboard and monitor as standard input and output devices.
A microcontroller is an entire computer manufactured on a single chip. Microcontrollers are usually dedicated devices embedded within an application. For example, microcontrollers are used as engine controllers in automobiles and as exposure and focus controllers in cameras. In order to serve these applications, they have a high concentration of on-chip facilities such as serial ports, parallel input output ports, timers, counters; interrupt control, analog-to-digital converters, random access memory, read only memory, etc. The I/O, memory, and on-chip peripherals of a microcontroller are selected depending on the specifics of the target application. Since microcontrollers are powerful digital processors, the degree of control and programmability they provide significantly enhances the effectiveness of the application.
Embedded control applications also distinguish the microcontroller from its relative, the general-purpose microprocessor. Embedded systems often require real-time operation and multitasking capabilities. Real-time operation refers to the fact that the embedded controller must be able to receive and process the signals from its environment as they are received. That is, the environment must not wait for the controller to become available. Similarly, the controller must perform fast enough to output control signals to its environment when they are needed. Again, the environment must not wait for the controller. In other words, the embedded controller should not be a bottleneck in the operation of the system. Multitasking is the capability to perform many functions in a simultaneous or quasi-simultaneous manner. The embedded controller is often responsible of monitoring several aspects of a system and responding accordingly when the need arises. The 8052 is the first microcontroller of the MCS-52 family introduced by Intel Corporation at the end of the 1970s. The 8052 family with its many enhanced members enjoys the largest market share, estimated to be about 40%, among the various microcontroller architectures. The architecture of the 8052 family of the microcontrollers is presented in this chapter. First, the original 8052 microcontroller is discussed, followed by the enhanced features of the 8032, and the 80C515.
In this chapter, the overview of the project, requirements of the project and need of 89S52 microcontroller are explained. In the next chapter, block diagram and schematic diagrams of the project will be explained.