| 摘要 |
A telephone ringer is light controlled, when the light intensity is below an adjustable preset level the ringer does not ring. The control element includes a SCR switching element, the gate potential of which is controlled by a light dependent resistance. A manual switch element to allow the telephone to be set ON, OFF, or AUTOMATIC is included. The AUTOMATIC setting is the light control element. The control element may be in the telephone set, or in a module insertable between set and system. The module additionally includes circuitry to allow phoning out. Courtesy and indicator light circuits are provided to allow dialing in the dark and incoming calls.
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