Introduction - If you have any usage issues, please Google them yourself
The project is using AVR microcontroller to generate a DTMF signal experiments, can complete a phone dialer features, while phone numbers can be displayed in the 1602 LCD panel, without the LCD panel can be removed that part of the circuit, producing would be easier. Speaker can use the phone Tingtongli speaker, so sound quality will be better, dial-up would be more accurate, it is recommended not to use the kind commonly used in passive experiments on-board buzzer, sound quality is poor.