| 摘要 |
An amplified telephone handset includes a current sensing circuit that senses the polarity of DC voltage supplied from a telephone base, irrespective of whether the DC voltage is of standard or reverse polarity. This feature allows the amplified telephone handset to operate with telephone bases that supply voltages through a telephone cord of either standard or reverse polarity. The amplified telephone handset also includes a voltage detection circuit that detects "off-hook" or "on-hook" states by detecting the absence or presence of the voltage. If a DC voltage is detected, then the amplified telephone handset is coupled to the telephone base and the voltage detection circuit disconnects the battery from receiver and transmitter circuits in the amplified telephone handset, placing the amplified telephone handset in a "on-hook" state. Conversely, when the amplified telephone handset is removed from the telephone base and no charging voltage is present, the voltage detection circuit connects the battery to the receiver and transmitter circuits in the amplified telephone handset, placing the amplified telephone handset in the "off-hook" state. An LED indicator on the amplified telephone handset indicates the level of electrical charge of the battery by the intensity of the LED diode.
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