三、双音频拨号电路徒弟:据说电话机有两种拨号方式,上面二讲都是介绍脉冲拨号电路,今天准备讲何内容? 师傅:电话机确有两种拨号方式,除了上讲所提的脉冲拨号方式,还有一种是双音多频拨号方式。本讲着重介绍双音多频拨号电路的工作原理及常见故障检 Third, dual tone dialing circuit Apprentice: It is said that there are two dial-up telephone, the above two are introduced pulse dialing circuit, what are the contents of today? Master: There are two dial-up telephone, in addition to mentioning Pulse dialing method, there is a dual tone multi-frequency dialing method. This talk focuses on the introduction of dual tone multi-frequency dialing circuit works and common fault detection