Robot Control using Cell Phone (DTMF)

DTMF (Dual Tone Multiple Frequency) is a very helpful tool when it comes to controlling any application, say a robot. Standard RC circuits have limited range, on the other hand a mobile phone can be used anywhere, where there is connectivity. Thus interfacing a robot with a Mobile will be quite cool.

For this i used a commonly available DTMF decoder MT8870DE. This IC requires a tone signal which is given by the earphone attached to the Mobile, and it decodes these two tone frequencies and gives digital output, representing the key that was pressed.

Basically on the caller side, it is a dial tone generator. When a key is being pressed on the matrix keypad, it generate a unique tone consisting of two audible tone frequency. For example, if the key '1' is being press on the phone, the tone you hear is actually consist of a 697hz & 1209hz sine signal. Pressing key '9' will generate the tone form by 852hz & 1477hz. The frequency use in the dial tone system is of audible range suitable for transmission over the telephone cable.

On the telephone exchange side, it has a decoder circuit to decode the tone to digital code. For example, the tone of 941hz + 1336hz will be decoded as binary '1010' as the output. This digital output will be read in by a computer, which will then act as a operator to connect the caller's telephone line to the designated phone line. The telephone exchange center will generate a high voltage signal to the receiving telephone, so as to ring the telephone bell, to notified the receiving user that there is an incoming call.
DTMF is a popular project especially in DSP (digital signal processing) subject. DSP software algorithm can be implement to generate as well as to decode DTMF tone.