本文介绍的简易内线电话交换机可接一条外线和十部分机,分机可相互呼叫,也可直拨外线。 整机电路如下页图所示。在话机未摘机之前,IC3⒀脚输出约14Hz脉冲信号,经R55、D22至IC2⒁脚,使IC2的Q1～Q0输出端依次循环触发VS1～VS10。同时,此脉冲又送至IC1复位端⒂脚,使IC1处于复位状态。假设9号话机摘机,a点电位因话机导通而下降。这时IC7a由于③ This article describes the simple intercom telephone exchange can pick up an outside line and ten extensions, extensions can call each other, but also direct dial outside. The whole circuit is shown in the following figure. Before the phone does not pick up the phone, IC3 ⒀ pin output about 14Hz pulse signal, the R55, D22 to IC2 ⒁ feet, so that IC2’s Q1 ~ Q0 output loop in turn trigger VS1 ~ VS10. At the same time, this pulse is sent to IC1 reset terminal pin, so that IC1 is in reset. Suppose handset 9 goes off-hook, a-point potential goes down due to the handset being on. At this time IC7a due ③