本文介绍的电路可接在电话进线处,用来指示话机的工作状态。与一般市售防盗报警装置相比,具有结构简单、方便易制的特点。电路如附图所示。当话机正常挂机时,线路中的48～60V电压使DW1导通,LED2发光;而D1由于反向偏置,因而LED1不发光。当外线有人盗打时,线路电压降至9V,DW1截止,LED2熄灭,同理LED1也不 This article describes the circuit can be accessed at the phone line, used to indicate the working status of the phone. Compared with the general market burglar alarm device, with a simple structure, convenient and easy system features. Circuit shown in the figure. When the phone hangs up normally, the voltage of 48-60V in the line turns DW1 on, and the LED2 emits light. Because D1 is reverse biased, LED1 does not emit light. When someone outside Pirates hit, the line voltage dropped to 9V, DW1 ends, LED2 goes out, empathy LED1 nor