This a sixth sense based telephone which i designed and developed from scratch for my open-ended project.It operates either through the good old 4x4 matrix keypad or recieves sixth sense data through the RX and TX pin on port 3, the two 8051's depending on the data recieved generate two sine-waves(one for low group and the other for high group) these are then added by an op-amp adder to generate the required dtmf tones
Revised : The 2nd revised circuit uses a single 8051 to produce the dtmf tones , the complete schematic and pcb details for the project is available in the link : http://www.pcbweb.com/projects/LvkaM2b1tHr0XEmyWx4b52CJ3f2C4Y (On my PCBweb account).