实验目的:结合DTMF拨号实验,按键检测实验和继电器实验,拨打电话.电话号码从键盘输入,挂机和摘机也从键盘上完成. F键是摘机,E键是挂机-Objective: combined with DTMF experiment, button detection experiments and relay experiment, call. Telephone number　the keyboard input, on hook and off hook　the keyboard to complete. The F key is off hook, the e key hang up