Design of intelligent telephone billing system based on AT89C52

In the design, the MCU AT89C52 is the core of the system. The system can send and receive the DTMF signal, which can identify the city telephone number or the long-distance telephone number. According the number, it can billing and show call duration and call cost. It can realize automatically the conversion between the full price and the discount price. It can billing accurately and conveniently query ticket information. It is configurable product and resets rate by pressing a button. It is low cost and low power consumption.