| 摘要 |
A data transmitter unit (22) for transmitting data over conventional telephone lines (26) from a remote location (24) to a central location (28). The data transmitter unit (22) derives its operational power supply from the telephone lines (26) to which it is interconnected, thereby doing away with the requirement for a separate power supply. The transmitter unit (22) includes ring detect circuitry (46) for detecting a ring signal on the telephone line (26). The ring detect circuitry (46) cooperates with the stand by power supply (38) charged by a charging circuit (36) to energize a logic module (44) and analog converter circuitry (40, 42) which is interconnected to sensors (30, 32). The logic module (44) controls operation of a tone generator (48) which transmits frequency signals representative of the input received from the sensors (30, 32) over the telephone lines (20, 26) to a central location (28). |
