DIGITAL PUBLIC TELEPHONE SET

PURPOSE:To change the analog public telephone set to the digital one in a short time by the same control without changing the appearance by exchanging a main board incorporating the basic function part of the analog public telephone set by the main boad incorporating the basic function part of the digital one. CONSTITUTION:When the analog telephone set is changed to the digital one, the borrowing part and the telephone line are removed from connection means 25-34 of the main board of the analog telephone set. Instead of it, the main boad for analog is removed and a main boad 2' for digital is connected to the borrowing part and the telephone line by the means 25-34. Thus, The 1st to 4th conversion parts 25',26', 31', and 33' are provided on the boad 2'. The conversion part 25 make an analog handset 3 correspond to a digital circuit 4'. A synchronizing circuit 26'b and a level exchange device 26'a are provided on the conversion part 26'. The level exchange device 31' a is provided on in the conversion part 31'. A DC-DC converter 33'a for power supply part 16 is provided on the conversion part 33'. Thus, the same function is given to the telephone set.