Device for connecting a subscriber line to a selected internal line

A device for connecting an information exchange subscriber line, such as a telephone, facsimile or telex line, to one of a plurality of internal lines, said device comprising a decoding means including discriminator means for recognizing rotary dialing disc pulses which have been distorted by telephone lines and exchanges of a calling apparatus, said discriminator means including timing means for determining a time region after an edge of a rotary dialing disc pulse and a coincidence means for ascertaining coincidence of an edge of a rotary dialing disc pulse and said time region, said device further including, connected to the input of said discrimination means, filter means for emphasizing the most significant portions of the distorted rotary dialing disc pulses, a sample and hold circuit connected to the output of said filter means for retaining said portions of rotary dialing pulses and a comparator means connected to said sample and hold means for comparing a predetermined fraction of the pulse value retained by said sample and hold circuit with an input pulse, said device further including a counter for counting a number of pulses equal to or smaller than the number of pulses of a predetermined initial test cipher and switching means controlled by said counter for setting the sample and hold means.