As a home hobbyist, there are many new projects that you can try to build. Do you have any interests on how to interface a microcontroller to the phone line? If you do, then today’s project is your preferred choice!
The main goal of this project is to develop a system to interface the telephone line with a microcontroller. By simply using the interface, any kinds of devices can be controlled using a telephone or mobile phone. The system will involve the use of DTMF tones, where it’s commonly being used in telephone networks.
For your information, Dual-Tone Multi-Frequency or also known as “DTMF” is the commonly signaling that being used for telephone signaling over the line in the voice-Frequency band to the call switching center. Every time when you’re dialing the touch tone phone, you’ll hear the tones that you’ve dialed!
Most of the standard DTMF keypad is perfectly laid out in a 4×4 matrix, with each row representing a low frequency and each column representing a high frequency. By pressing any keys, it will send a sinusoidal tone of the two frequencies (697 and 1209 Hz). Since the original keypads have levers inside, hence each button activated two contacts. The multiple tones are the main reason for calling the system multifrequency. After it, these tones will be decoded by the switching center to determine which key the user pressed!