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The intelligent telephone alarm system is designed with a single chip microcomputer as the core of system,and the intelligent system is controlled by AT89C51. A telephone network is used as transmission of voice digital information in the system. The telephone alarm is composed of a single-chip microcomputer control, sensor and signal input circuit, and DTMF send and receive circuit, voice controlling and receiving circuit, alarm telephone circuit. According to the different sensor output signal, it can send out different alarm information to realize remote monitoring function.

In this paper, based on the traditional fixed telephony features to increase the short message processing module. To meet the voice communication between users, the fixed telephone can realize mutual development between the SMS function .The main telephone lines in the completion of the CAS signal detection, and traditional communications in FSK and DTMF signal reception and transmission.

DTMF (Dual Tone Multi Frequency) is a system of signal tones used for telecommunications. DTMF uses two tones to represent each key on the touch pad. DTMF data transfer technique has advantages such as high reliability, constant speed, and high signal to noise ratio, low cost and optimal utilization of existing resources. These features make DTMF an attractive Data Transfer Technique. It finds application in home and car security systems, robot control, SMS and voice call controlled industrial applications. In this paper, we discuss the use of DTMF data transfer in a voice call to control a toy car. Cell phone 1(CP 1), which is at user end, makes a call to cell phone 2(CP 2) at the machine end and establishes a connection. A key is pressed at the user side. Two tones corresponding to one key are encoded and sent through the cell phone network. Both tones are tapped through the earphone jack of cell phone at machine end and are decoded. The output is fed to a Micro-controller. The Micro-controller is connected to the remote control unit of the toy car, which in turn controls the motion of the car. The car moves in various directions according to the key pressed user. The electronic circuit is divided into 2 parts. The transmitter side consisting of Cell phone 1 with an inbuilt encoder and the receiver side consisting of Cell Phone 2, 8870 DTMF decoder and Atmega 16 micro-controller. The programming has been carried out on AVR Bascom®.