电话机用户有时会遇到这种情况:打完电话后,话筒未搁好,外面的电话打不进来,其它的同线电话打不出去,既耽误了正常工作,又浪费了电话费。在此介绍一个简单的小电路,它可用于提醒电话机用户将话筒搁好。附加电路独立于话机电路,仅借用话机电源,因此不影响原机功能,具体电路见附图。L_1、C_1和IC1A构成一个基频振荡电路, Telephone users sometimes encounter such a situation: after the call is finished, the microphones are not properly placed, the outside telephone can not be brought in and the other same-line telephone can not be called out, which delays the normal work and is wasted the telephone bill. Here’s a simple little circuit that can be used to remind the phone user to put the mic on hold. Additional circuits independent of the phone circuit, only borrow phone power, so does not affect the original machine features, the specific circuit see the photo. L_1, C_1 and IC1A constitute a baseband oscillator circuit,