28-09-2012, 04:41 PM
INTERACTING COLLEGE MOBILE SYSTEM
INTERACTING COLLEGE.doc (Size: 617 KB / Downloads: 43)
Synopsis
Any new student or any new person entered in to the college campus without knowing any thing about college regarding where the class rooms, labs, staffroom and Etc., our project will help to guide the them, in this project students and college will have the communication without any reception counters in the college campus, any student are required any information they can communicate with the help off this system and they can get it is very easily.
This prototype model has mainly very big advertisement panel display. But our prototype has 4x40 LCD display. The students go to the colleges. Some instructions are written there place and mobile number also. So the students is making call and sends data to that mobile number. Another mobile automatically lifted and display information on display panel.
Here we are using microcontroller, it is heart of this project. The controller gets data from buffer along with digital tone modulated frequency when the customer is sent data from mobile to other. Here we are using EEPROM memory IC. Because number of advertisement stored into memory chip which company product. This process repeated. The controller gets ready response to next enquiry of the data. So the microcontroller sends whatever message stored in memory chip to display unit.
The oscillator is used for to perform working speed of the microcontroller. Here the program enable pin is high then whatever code dumped into flash memory of the microcontroller. It will be executed. When the microcontroller will get hangover then apply the reset. The process is repeatedly.
Introduction
The purpose of this Application Note is to provide information on the operation and application of DTMF Receivers. The MT8870 Integrated DTMF Receiver will be discussed in detail and its use illustrated in the application examples which follow. More than 25 years ago the need for an improved method for transferring dialing information through the telephone network was recognized. The traditional method, Dial pulse signaling, was not only slow, suffering severe distortion over long wire loops, but required a DC path through the communications channel. A signaling scheme was developed utilizing voice frequency tones and implemented as a very reliable alternative to pulse dialing. This scheme is known as DTMF (Dual Tone Multi- Frequency), Touch-Tone™ or simply, tone dialing. As its acronym suggests, a valid DTMF signal is the sum of two tones, one from a low group (697-941Hz) and one from a high group (1209-1633Hz) with each group containing four individual tones. The tone frequencies were carefully chosen such that they are not harmonically related and that their intermediation products result in minimal signaling impairment. This scheme allows for 16 unique combinations. Ten of these codes represent the numerals zero through nine, the remaining six (*, #, A, B, C, D) being reserved for special signaling.
Development
Early DTMF decoders (receivers) utilized banks of band pass filters making them somewhat cumbersome and expensive to implement. This generally restricted their application to central offices (telephone exchanges). The first generation receiver typically used LC filters, active filters and/or phase locked loop techniques to receive and decode DTMF tones. Initial functions were commonly, phone number decoders and toll call restrictors. A DTMF receiver is also frequently used as a building block in a tone-to-pulse converter which allows Touch-Tone dialing access to mechanical step-by-step and crossbar exchanges.
The introduction of MOS/LSI digital techniques brought about the second generation of tone receiver development. These devices were used to digitally decode the two discrete tones that result from decomposition of the composite signal. Two analog band pass filters were used to perform the decomposition.
Totally self-contained receivers implemented in thick film hybrid technology depicted the start of third generation devices. Typically, they also used analog active filters to band split the composite signal and MOS digital devices to decode the tones. The development of silicon-implemented switched capacitor sampled filters marked the birth of the fourth and current generation of DTMF receiver technology. Initially single chip band pass filters were combined with currently available decoders enabling a two chip receiver design. A further advance in integration has merged both functions onto a single chip allowing DTMF receivers to be realized in minimal space at a low cost.
Inside The MT8870
The MT8870 is a state of the art single chip DTMF receiver incorporating switched capacitor filter technology and an advanced digital counting/ averaging algorithm for period measurement. The illustrates the internal workings of this device.
To aid design flexibility, the DTMF input signal is first buffered by an input op-amp which allows adjustment of gain and choice of input configuration. The input stage is followed by a low pass continuous RC active filter which performs an ant aliasing function. Dial tone at 350 and 440Hz is then rejected by a third order switched capacitor notch filter. The signal, still in its composite form, is then split into its individual high and low frequency components by two sixth order switched capacitor and pass filters.
Each component tone is then smoothed by an output filter and squared up by a hard limiting comparator. The two resulting rectangular waves are applied to digital circuitry where a counting algorithm measures and averages their periods. An accurate reference clock is derived from an inexpensive external 3.58MHz cloudburst crystal.