ELECTRONIC TONE RINGER

摘要

ELECTRONIC TONE RINGER An electronic tone ringer responds to ringing signals on a telephone line while being unresponsive to dialing pulses or other signals on the line. Powered directly from the telephone line or alternatively from an external DC supply, the ringer distinguishes between valid and invalid ringing signals. A distinctive ringing capability for the tone ringer is also available through the use of two oscillators which allow selection of four frequencies and four modulation rates.