i allready worked on this project with dtmf module and arduino for driving small robo car and switching relay .....
The input unit of the DTMF module is basically used to receive the DTMF audio output from a mobile phone.....
The decode unit reads the tones received from the input unit and converts (decodes) these tones to their equivalent digital value. The digital values are the binary representation of the numbers 0, 1, 2, 3, 4… etc in the form of 0 and 1. Then these 0s and 1s are sent to the output unit.