| 摘要 |
PURPOSE:To improve the operability and to prevent the occurrence of improper call by providing a photodetection means detecting the surrounding lightness and a sound volume variable means controlling variably the sound volume of a call tone in response to the result of detection of the photodetection means. CONSTITUTION:A voltage controlled variable resistor 62 is provided to the input of an output amplifier 60, the resistance is controlled by a photoelectric converter 63, photoelectric converters 62, 45 are provided to apply on/off control to a threshold value voltage detection circuit 40 and an output voltage of the photoelectric converter 45 applies on/off control to the circuit 40. Since sufficiently large luminous quantity exists at a location at daytime or with lighting, the output voltage of the photoelectric converters 45, 63 is both high, and when a call signal comes with this state, an incoming detection signal is generated from the circuit 40 and a call tone signal is generated from a call tone generating circuit 50, and the call tone signal is amplified by an output amplifier 60 as it is without being subject to large attenuation by the resistor 62.
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