This paper introduces a kind of device that can transfer collinear telephones automatically .The device can make every extension share the call signal of the telephone line. The user can call any extension accurately . And every extension keep secret to the other extension when it calling the outside . This equipment must realize the function is when the outwire comes the telephone, this equipment may the auto answer and the automatic branching call. The concrete working is: 1), the outwire comes when the telephone the main engine through picks automatically to the ringing examination machine. 2) the voice prompt outwire user side presses down the extension number which wants. 3) the extension telephone telephone bell, after the called subscriber hears the ting, picks machine. 4), once is called the extension subscriber to pick machine, this equipment immediately the automatic shut-off main engine circuit and will block other extension telephones, will cause the telephone to enter the normal call condition. This party line automatic adapter's core part is AT89S51 which ATMEL Corporation produces, it is one kind has the 4k byte to scratch quickly writes the programmable/cleaning non-erasable storage. Moreover the power loss is low, the performance is good, the reliability is high. The device carries the hardware and software electric circuit into effect ,designing simple ,the price is cheap ,and can connect the telephone line directly, installing also very convenient.
