Discriminating means for telephone circuits

摘要

An electronic circuit for use with telephone instruments or the like in those cases where so-called "dial tap" is encountered, whereby a buzzer or bell included as part of the telephone instrument is adversely affected when the dial is rotated for purposes of dialing a particular call number. The circuit provides a discriminating function against the short term dial pulses by blocking them, but allows ringing current to pass substantially unaffected.