实际中常常会遇到这样的情形,一些办公室或家庭同时安装几部电话(如单位内部电话和外线直拨电话)。在来电话时,常使人弄不清是哪部电话机在响铃,这里介绍一种实用的电话振铃显示电路。 1 电路原理 如图中虚线部分所示,当振铃脉冲到来时,整流后的正脉冲,通过二极管D_1和电阻R_1加至D_2上并使D_2发光,同时给电容C_1充电。脉冲过去后,电容 In practice, it is often the case that some offices or homes have several phones installed at the same time (such as internal and external direct-dial phones). When making a phone call, people are often confused about which phone is ringing. Here is a practical telephone ringing display circuit. 1 circuit principle As shown in the dashed part, when the ringing pulse arrives, the rectified positive pulse through the diode D_1 and resistor R_1 added to D_2 and make D_2 light, while the capacitor C_1 charge. After the pulse has passed, the capacitor