Radio telephone system

Abstract: In a radio telephone system comprising a radio telephone set (3) utilizing a rechargeable battery (20) and a base unit (2) connected to the radio telephone set (3) through a radio chan­ nel for exchanging a speech signal between the radio telephone set (3) and a wired telephone line, there are provided a detector (21) for detecting the charged state of the battery (20), a ter­ minating device (22, 23) responsive to the output signal of the detector (21) for terminating the radio channel between the ra­ dio telephone set (3) and the base unit (2).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a radio telephone system comprising a radio telephone set utilizing a rechargeable battery as its electric source, and a base unit connected to the radio telephone set through a radio channel and through which speech signals are transmitted between the radio telephone set and a wired telephone line, and more particularly, a radio telephone system capable of prohibiting a continuous transmission state caused by the failure in the operation of a speech channel termination switch while the battery of the radio telephone set is being charged. 2. Description of the Prior Art As is well known in the art, a prior art radio telephone system is constituted by a base unit connected to a wired telephone line, and a radio telephone set controlled by the base unit for exchanging speech signals between the radio telephone set and the wired telephone line. When an origination switch in the radio telephone set is operated, a control circuit controls a transmitter and a receiver to establish a radio speech channel between the radio telephone set and the base unit, thus permitting speech. When the speech is terminated, a termination switch is closed for terminating the speech channel. In an ordinary telephone set, the origination and the termination of the speech channel are effected by on-hook and off-hook operations of a handset of the telephone set, but in some type of the radio telephone systems, the origination and the termination of the speech channel are controlled by independent switches. In such a system, if the speech channel termination switch fails to be operated when the speech has terminated, the speech channel between the base unit and the radio telephone set, and further between the base unit and the wired telephone line will remain in the speech state, thus prohibiting the channel from being used for other speeches. Especially, in a system constructed such that the radio telephone set is mounted on and connected to the base unit when not in use so as to charge the battery in the radio telephone set and is dismounted when in use, since electricity in the electric source is not consumed during the charging, the speech state will be maintained until the trouble is noticed and the speech channel termination switch is operated. For this reason, a display device or a warning device has been used for informing the fact that the speech state is maintained or a timer is provided for automatically terminating the speech channel when the speech state is maintained beyond a predetermined period. In the system in which whether the telephone system is in the speech state or not is informed by a display device, the display is likely to be mistaken as a display of other display devices so that there is a defect that the speech channel termination switch cannot be operated correctly. Where the speech channel is forcibly terminated, there will be a case in which the speech channel is unfavourably terminated during actual talking. A radio telephone apparatus with a rechargeable battery is known from US-A-4 511 761. JP-A-58 125 922 describes how a radio telephone set can turn off automatically in the absence of a radio link. A radio telephone which provides automatic hang-up after a period when no speech or operational code signals are received is described by US-A-3 557 312. SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved radio telephone system to prevent a speech channel from being in continuous use state without interfering an actual speech even when a user of the telephone set forgets to perform a speech channel termination operation. According to one aspect of the invention there is provided a radio telephone system comprising a base unit connected to a wired line and a radio telephone set utilizing a rechargeable battery as an electric source and connected to said base unit through a radio channel, said base unit including a first transmitter and a first receiver for establishing the radio channel with said radio telephone set, said radio telephone set including a second transmitter and a second receiver for establishing the radio channel with said base unit, said base unit further including a power circuit for charging said rechargeable battery of said radio telephone set when said radio telephone set is mounted on said base unit and detecting means for detecting a charging state of said rechargeable battery, and further comprising control means having timer means started in response to a detection output of said detecting means for measuring a predetermined time, for forcibly turning off said first transmitter on the basis of an output of said timer means indicative of termination of the time measurement. A second aspect of the present invention provides a radio telephone system comprising a base unit connected to a wired line, a radio telephone set utilizing a rechargeable battery as an electric source and connected to said base unit through a radio channel and a battery charger on which said radio telephone set is detachably mounted, said battery charger having a power circuit for charging said rechargeable battery of said radio telephone set, said base unit including a first transmitter and a first receiver for establishing the radio channel with said radio telephone set, said radio telephone set including a second transmitter and a second receiver for establishing the radio channel with said base unit, and wherein said radio telephone set comprises: detecting means for detecting a charging state of said rechargeable battery; and control means having timer means started in response to a detection output of said detecting means for measuring a predetermined time, for forcibly turning off said second transmitter on the basis of an output of said timer means indicative of termination of the time measurement. More particularly, by utilizing the fact that after completion of a speech, the radio telephone set is connected to the base unit so as to charge the battery in the radio telephone set, according to this invention, after termination of a speech, the initiation of charging of the battery is detected and the radio channel is terminated in accordance with the detection. Consequently, according to this invention, initiation of the charging of the battery when a speech is terminated is detected and the detection is used as a speech termination procedure so that continuous use of a speech channel can be prevented even when the user forgets the speech channel termination procedure. Since the speech channel is terminated after termination of an actual speech, no trouble is caused in the actual speech and the speech channel is available for other speeches. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig.1 is a block diagram showing one embodiment of this invention; Fig.2 is a connection diagram showing one example of a detection circuit; Fig.3 is a block diagram showing a modified embodiment of this invention; and Fig.4 and 5 are flow charts showing the operation of the embodiments of this invention. DESCRIPTION OF THE PREFERRED EMBODIMENT In a preferred embodiment of this invention shown in Fig.1, a speech signal from a wired telephone line 1 is transmitted to a receiving antenna 12 of a radio telephone set 3 via a hybrid circuit 9, a transmitter 10 and a transmitting antenna 11. The received signal is transmitted to a speaker 13 via a receiver 5. A speech signal inputted into a microphone 14 of the radio telephone set 3 is transmitted through a transmitter 6, a transmission antenna 15, a receiving antenna 16, a receiver 17 and the hybrid circuit 9 to the wired telephone line 1. In a base unit 2, an AC/DC converter 18 energized by a 100 volt alternative current source is utilized and its output is used to charge a battery 20 of the radio telephone set 3 through contacts 19A and 19B. The radio telephone set 3 can be used separately from the base unit 2 by disconnecting the contacts 19A and 19B. After completion of the speech, if a user fails to operate a speech channel termination switch 7 and connects the radio telephone set 3 to the base unit 2, a detection circuit 21 detects that the battery charging starts. Then, in response thereto, a control circuit 22 disconnects the transmitter 10 from the power source (AC/DC converter 18), thus disabling the transmitter 10. When the receiver 5 detects an interruption in a radio wave from the transmitter, a controller 23 disables transmitter 6 in the radio telephone set to bring it to a waiting state, thus preventing unfavorable continuous transmission. In this case, a circuit for detecting the radio wave interruption can be constituted by a known noise squelch or carrier squelch circuit. An origination switch 4 and the speech termination switch 7 may be combined into a single switch which is used for origination by turning it on and for speech termination by turning it off. The charging contacts 19A and 19B may be constituted by metal pieces or plug and jacks. Fig.2 shows one example of the detection circuit 21, in which the output terminal of the AC/DC converter 18 is connected to a terminal 24 which is connected to contact 19A through a resistor 25 for determining the charging current, and to an inverting input of a comparator 28. The voltage at the terminal 24 is divided by resistors 26 and 27 and the divided voltage is applied to a non-inverting input of the comparator 28. Suppose now that the input voltage to the terminal 24 is 10V, the voltage after charging (maximum voltage) of battery 20 is 7V, the resistors 26 and 27 have resistance value of 100 kΩ and 1MΩ, respectively. Then at the time of not charging, a voltage 10V x {1MΩ + (100kΩ + 1MΩ)} = 9V is applied to the non-inverting terminal of the comparator 28, whereas 10V is applied to the inverting terminal so that the voltage at an output terminal 29 of the comparator 28 is at a low level (about 0V). On the other hand, at the time of charging, since a voltage of less than 7V is applied to the inverting terminal, the voltage at the output terminal 29 becomes a high level (= the driving voltage V cc of comparator 28). Consequently, the output voltage of comparator 28 becomes a high level. Thus, whether the battery is being charged or not can be detected from the output of the comparator 28. The detecting circuit 21, can be substituted by a CMOS inverter or the like. Further the detecting circuit 21 may be installed in the radio telephone set 3 so as to stop the transmission of the electric wave from the radio telephone set 3. Instead of installing the AC/DC converter 18 in the base unit 2, an AC/DC converter 30 can be installed on the outside of the base unit 2 as shown in Fig.3 so as to detect the charging state on the side of the radio telephone set 3. Fig.4 shows the operation of the above-described embodiment. In the flow chart shown in Fig.4, at steps 31 and 32, a judgment is made as to whether the charging has been made for a predetermined period or not. The purpose of step 31 is to assure the speech channel by disconnecting the radio telephone set from the charging source at once when it is inadvertently connected to the charging source. On the other hand, the purpose of step 32 is to assure the speech channel when the electric wave is temporarily interrupted due to fading etc. Fig.5 is a flow chart showing the operation of another embodiment. In the flow chart of this embodiment, a step 33 for detecting whether or not the battery is currently being charged is added to the steps in the Fig.4. In this embodiment, the speech channel is established while the battery is being charged. Instead of providing a detector for detecting whether the battery is being charged or not in the base unit or a radio telephone set, it is possible to provide the detector for both the base unit and the radio telephone set. With this construction, both the base unit and the radio telephone set are turned off in response to the output of the detector.

Claims: A radio telephone system comprising a base unit (2) connected to a wired line (1) and a radio telephone set (3) utilizing a rechargeable battery (20) as an electric source and connected to said base unit (2) through a radio channel, said base unit (2) including a first transmitter (10) and a first receiver (17) for establishing the radio channel with said radio telephone set (3), said radio telephone set (3) including a second transmitter (6) and a second receiver (5) for establishing the radio channel with said base unit (2), said base unit (2) further including a power circuit (18) for charging said rechargeable battery (20) of said radio telephone set (3) when said radio telephone set (3) is mounted on said base unit (2) and detecting means (21) for detecting a charging state of said rechargeable battery (20), characterised by: control means (22) having timer means started in response to a detection output of said detecting means (21) for measuring a predetermined time, for forcibly turning off said first transmitter (10) on the basis of an output of said timer means indicative of termination of the time measurement. A radio telephone system according to claim 1, further characterised in that said radio telephone set (3) comprises control means (23) for monitoring an electric wave transmitted from said first transmitter (10) of said base unit (2) and received by said second receiver (5) and forcibly turning off said second transmitter (6) when no electric wave is received from said first transmitter (10). A radio telephone system according to claim 1, further characterised in that said radio telephone set (3) comprises detecting means (21) for detecting the charging state of said rechargeable battery (20) and control means (23) having timer means started in response to the detection output of said detecting means (21) for measuring a predetermined time, for forcibly turning off said second transmitter (6) on the basis of an output of said timer means indicative of termination of the time measurement. A radio telephone system comprising a base unit (2) connected to a wired line (1), a radio telephone set (3) utilizing a rechargeable battery (20) as an electric source and connected to said base unit (2) through a radio channel and a battery charger (30) on which said radio telephone set (3) is detachably mounted, said battery charger (30) having a power circuit for charging said rechargeable battery (20) of said radio telephone set (3), said base unit (2) including a first transmitter (10) and a first receiver (17) for establishing the radio channel with said radio telephone set (3), said radio telephone set (3) including a second transmitter (6) and a second receiver (5) for establishing the radio channel with said base unit (2), characterized in that said radio telephone set (3) comprises: detecting means (21) for detecting a charging state of said rechargeable battery (20); and control means (23) having timer means started in response to a detection output of said detecting means (21) for measuring a predetermined time, for forcibly turning off said second transmitter (6) on the basis of an output of said timer means indicative of termination of the time measurement. A radio telephone system according to claim 4, further characterised in that said base unit (2) comprises control means (22) for monitoring an electric wave transmitted from said second transmitter (6) of said radio telephone set (3) and received by said first receiver (17) and forcibly turning off said first transmitter (10) when no electric wave is received from said second transmitter (6).

Inventors: ITO KOICHI, KATO KAORU, SAEGUSA NOBORU, SASAKI ISAO, TOKI AKIO, YOSHIZAWA KAZUHIRO, YOTSUTANI AKIO, ITO, KOICHI, KATO, KAORU, SAEGUSA, NOBORU, SASAKI, ISAO, TOKI, AKIO, YOSHIZAWA, KAZUHIRO, YOTSUTANI, AKIO
Applicants: NIPPON ELECTRIC CO, NIPPON TELEGRAPH & TELEPHONE, TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA, NEC CORPORATION, NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1986
Main classification: H04M1
IPC codes: H04B7, H04M1