This circuit detects the dial tone (DTMF Tone) from a telephone line and decodes the keypad pressed on the remote telephone. The dial tone we heard when we pick up the phone set is call Dual Tone Multi-Frequency (DTMF). The name was given because the tone that we heard over the phone is actually make up of two distinct frequency tone, hence the name dual tone. The DTMF tone is a form of one way communication between the dialer and the telephone exchange. A complete communication consist of the tone generator and the tone decoder. In this article, we are use the IC MT8870, the main component to decode the input dial tone to 5 digital output. These digital bits consists of pressed key code 4-bit and 1-bit to tell that data is available. It can be interface to a microcontroller for further application such as remote control, IVRS (Interactive voice control systems) etc. Continue reading DTMF Decoder MT8870