Phone to Microcontroller interfacing with DTMF

How to interface a microcontroller to the phone line. The tones you hear as you enter numbers on your phone can remotely control devices. Learn how to use these DTMF tones in your microcontroller projects. This article was submitted by Mayank Magoo as part of the Hobby parts for articles  program. Mayank received a Arduino compatible Modern Device Company
Phone to Microcontroller interfacing with DTMF - schematic

Bare Bones Kit for this great article. This project describes the development of a system to interface the telephone line with a microcontroller. Using this interface any device can be controlled using a telephone or cell phone. The system involves the use of DTMF tones commonly used in telephone networks. Dual-Tone Multi-Frequency ( DTMF ) signaling is used for telephone signaling over the line in the voice-Frequency band to the call switching center. These are the tones you hear when you dial a touch tone phone. The standard DTMF keypad is laid out in a 4G—4 matrix, with each row representing a low frequency, and each column representing a high frequency. Pressing a single key will send a sinusoidal tone of the two frequencies at the same time, the lower frequency for the row of the pressed key and the higher tone for the column. These tones are then decoded at the receiving end to determine which key was pressed. The use of two tones for a single key ensures that no two keys will generate the same signal. There are 16 possible tone sets but only 12 are used on common telephones. The ATMEGA-8 microcontroller was selected due to it`s low cost and it`s 8Kb of programmable flash memory and 512 bytes of EEPROM and ease of programming and implementation. The MT8870 is a low cost DTMF Decoder which gives a 4-bit binary output characteristic of each tone and a status signal which has logic high whenever a valid DTMF tone is...

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