Telephone hold attachment

Abstract

A hold attachment for a single-line telephone to allow the user to replace the handset and resume a call later or at another location. The attachment consists of a non-polarity-sensitive substitution circuit which is connected across the telephone line without regard for line polarity, the circuit including a bridge rectifier, a zener diode, the winding of a holding relay, a light-emitting diode and a manual switch, the contacts of the relay being connected in parallel with the switch. To place a call on 'hold', the switch is operated while the handset is placed on hook, and then released. The line voltage causes the zener diode to conduct and energizes the relay, whereby the relay contacts shunt the switch, which maintains the holding connection across the line after the switch is released, and which provides a load resistance such that the switching equipment in the central office will remain held up, maintaining the talking connections to the called telephone. The hold condition is released by lifting the handset of this or any other telephone on the same line. This reduces the resistance across the line sufficiently to drop the line voltage below the zener-sustaining value, causing the relay to release. The light-emitting diode is illuminated during the hold period and is extinguished upon release of the relay.