| 摘要 |
PURPOSE:To detect surely the operation stop of an automatic answering telephone set by utilizing a line supervisory pulse generated for plural number of times after on-hook of a caller. CONSTITUTION:When a caller hooks on, since the line supervisory pulse is generated for plural number of times, a public transistor of a photocoupler 9 is turned on/off. Then the electric charge of a capacitor 20 is discharged by the on/off of the transistor (TR), TRs 21,23 are turned on and this stage is held. The holding output is detected by a system control circuit 10 and an output RL goes to logical 1. Then the TR 12 is turned off and no current is fed to a relay 14, then a relay contact 2 is turned off to interrupt telephone lines L1,L2 to a tape recorder.
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