问:电话机除了前面两讲所述的咏冲拨号方式,还有无其它的拨号方式?答:电话机共有两种拨号方式,即脉冲拨号方式和双音频拨号方式。本讲主要介绍双音频拨号方式的工作原理及常见故障的检修。问:双音频拨号电路是如何组成的?答:如图1所示,双音频拨号又称之为 DTMF 拨号,其电路由启动电路、电子开关和开关控制器、DTMF 放大器、电源电路、DTMF 拨号集成电路和键盘组成。 Q: Is there any other dialing method besides the two dialing methods mentioned in the previous two talk? A: The telephone has two dialing modes, pulse dialing and dual tone dialing. This talk mainly introduces the working principle of dual tone dialing method and maintenance of common faults. A: As shown in Figure 1, dual tone dialing is also known as DTMF dialing. The circuit consists of start-up circuit, electronic switch and switch controller, DTMF amplifier, power circuit, DTMF dialing Integrated circuit and keyboard.