INCOMING INFORMATION CIRCUIT OF KEY TELEPHONE SET

摘要

PURPOSE:To inform incoming through a single tone ringer by providing a monitor relay for a power source, and connecting the tone ringer to a leased trunk line through its contact in a power-on state or to a channel side in case of a power failure. CONSTITUTION:A speech line Lt1 is connected to line terminals a1 and b1 of the key telephone set, a trunk line Lp2 is connected to line terminals a2 and b2, and a signal line Ls1 is connected to line terminals d1 and d2. The single tone ringer TRG is bridge-connected to the side of the talking circuit TKC of contacts lr<0> and lr<1> and the trunk line Lp2 through contacts Pf<0> and Pf<1> of the monitor relay for the power source. A speaker SP is driven through a transformer 3 according to the arrival of a call signal from the trunk line Lp2 in the feeding of a commercial power source and in response to the arrival of the call signal from the trunk line Lp2 or signal arrival of the call signal from the trunk line through a speech line lt1 when a connection is made by a main device according to a selection made by the contacts lr<0> and lr<1> in case of a power failure. Thus, incoming is annunciated through the single tone ringer.