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Decoder Device for Caller ID
The project was created to provide a solution for storing unlimited caller ID phone numbers by showing its schematic and software required for decoding and storing the data.
From the normal operation of caller ID system, the telephone company sends the modulated caller ID data between the first and second rings, at a speed of 1200 Baud 9N1. The Caller ID module interprets the data once it has been demodulated then displays the phone number and name. The encoding of data includes 2 standards consisting of Simple Data Message Format (SDMF) and Multi data Message Format SDMF was used first to support the caller phone number and time then MDMF supports the phone number, name, time, and locality.
The MT8843 demodulator is utilized by this caller ID where the demodulated serial data comes out of pin 17 at a rate of 1200 bauds if the chip is in mode 0. By connecting pin 9 to ground, the mode 0 is selected. Ensuring the compatibility of voltages levels will enable the sending of data to the computer where the TTL data coming out from the chip has to be converted to the RS232 levels.