DE2822069A1 - CIRCUIT ARRANGEMENT FOR EARNING PROTECTION IN VOICE-CONTROLLED HANDS-FREE SYSTEMS, IN PARTICULAR IN TELEVISIONS - Google Patents

Description

H. Wiedmann-lO

Circuit arrangement for protection against eavesdropping in voice-controlled hands-free devices, in particular in telephone sets.

The invention relates to a circuit arrangement in the preamble of claim 1 mentioned Art.

On a hands-free device, the incentive and the release of a connection are usually carried out by means of a button. Such a hands-free device can in particular also be part of a telephone set that leaves the choice free, whether you are talking on the handset or the hands-free system. If the handset is used, it is the participant is forced to hang up the handset at the end of the call and thus trigger the connection. in the In contrast to the handset operation, the subscriber is not forced to do anything when using the hands-free facility to do. It can therefore easily happen that you forget to reset the handsfree key, i.e. to release the connection will. The speakerphone is still switched on. The interlocutor can still have conversations in the room of the first Listen in on the subscriber without the latter noticing that he is being eavesdropped. If there is no reverse release, the case may still be the case occur that the call partner is blocked.

To the participant on the not triggered state of the speakerphone point out, it is known to provide a control light in the handsfree button. Furthermore, one leaves the The handsfree key protrudes clearly from the housing of the telephone set after actuation, or the square handsfree key is rotated when actuated, so that the triggering requirement is good from its markedly changed position is recognizable. However, all of these known remedies tread the optical path that fails when the hands-free device is no longer in the field of vision of the participant after the end of the conversation. For example, this occurs when the participant

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wherever j η is talking to another part of the room.

An acoustic indicator, which is desirable in itself and which indicates the operation of the hands-free device, acts during the Telephone conversation very annoying.

The invention is based on the assumption that the interlocutor has two possible behavior when he notices that he is the can listen to the first participant.

Either he will try to make himself noticeable in order to free his own line; his acoustic signals, Calling, whistling etc. can be heard in the loudspeaker of the first participant (the minimum volume must be guaranteed), who thereby becomes attentive and can switch off the device.

Or the interlocutor is interested in the conversations of the first participant and would like to listen to them; he will

keep as quiet as possible (hand over the microphone), so as not to attract the attention of the first participant.

The invention has now set itself the task of a circuit arrangement to create the type mentioned in the preamble of claim 1, while taking advantage of the last-mentioned Behavior of the interlocutor the first participant is given an alert that tells him about the If the hands-free system is not triggered, information is also provided in areas of the room that are far from the hands-free system *

This object is achieved by the features characterized in claim 1.

Due to the room noise level, the speakerphone becomes

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of the first participant if there is no reception signal from the other party, switched via their own voice control in such a way that that the transmission path is released and the reception path is attenuated. DC criteria for this are usually the Voice control available, which form the control signals for the two control amplifiers.

During a normal conversation, the control signal direct current changes depending on the pauses in the conversation of the first participant or depending on the interim remarks of the interlocutor. It is therefore unnatural if the transmission direction is continuously open with an intact hands-free system.

If a higher or maximum control signal direct current flows for the transmission path for a certain time (for example J> 0 s), an abnormal conversation condition exists, which can also be the condition of being listened to. It is therefore very easy to give a discreet acoustic warning signal if this control signal direct current exceeds a predetermined duration. Of course, the control signal direct current determined for the reception path can also be used equally as a control criterion.

The invention will now be described in greater detail on the basis of exemplary embodiments explained. Show it:

1 shows a circuit arrangement of a hands-free device with a bug protection circuit according to the invention and

2 shows an alternative anti-eavesdropping circuit according to the invention.

Fig. 1 shows a circuit arrangement which is part of a telephone set can be. A microphone M is via a transmitter

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designaldetektor Dl and a control amplifier RVl with the outgoing Four-wire output is connected to a fork circuit G. Of the The two-wire output of this hybrid circuit can be connected to a subscriber line L. The coming four-wire exit the hybrid circuit G is connected to the loudspeaker LS via a received signal detector D2 and a further control amplifier RV2 tied together. Control connections lead from the detectors D1, D2 to a voice control circuit ST, from which further control connections lead to the control amplifiers RV1, RV2.

A control connection also leads from the output of the voice control circuit ST connected to the control amplifier RV1 a bug protection circuit AS, which is indicated by dashed lines. This control connection is to the input of a Threshold switch SS connected, the output side via a break contact of a non-latching key T is connected to the input of a timing element Z. The pointer Z is like this designed so that it emits a signal after a predetermined period from its activation. This duration can be adjusted and be for example 30 seconds. The output of the timing element Z is connected to the control input of a connecting element A. A warning supply source Q is provided by means of the connection element A Can be connected to an acoustic alarm transmitter W. The warning source Q can be a low-frequency oscillator, while a small loudspeaker can be used as a warning device.

The hands-free system works as follows. Voice control is in the idle position of the hands-free system set so that they are connected to the control amplifier RV1, RV2 emits control signals causing average gains. If the participant discusses the microphone M, the transmission signal detector speaks Dl and outputs an analog control signal to the voice control circuit ST, which - if from the interlocutor there is no voice signal - the control amplifier RVl to a higher gain and the control amplifier RV2

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sets a correspondingly lower gain. If, on the other hand, there is a voice signal from the conversation partner, this will be recognized by the received signal detector D2, which, similar to the detector Dl, causes the gain of the control amplifier RVl from the quiescent value to a lower value and the gain of the control amplifier RV2 from the quiescent value to a higher one Value increases. In this way, on the one hand, the transmission path and, on the other hand, the reception path can be fully opened. It is also possible, to assume a different rest position. For example, even with a low sound level at the microphone M, the transmission path can be be fully open when the reception path has no signal. The control signals have fluctuating direct current values.

For the first-mentioned case of the amplification rest position, the threshold value circuit SS is dimensioned in such a way that it only responds to control signals whose values are above those for the rest amplification. For the last-mentioned case of the amplification rest position, the threshold value circuit SS is dimensioned so that it only responds to control signals of maximum strength. If a higher or maximum control signal direct current flows to the control amplifier RV1, the threshold value circuit SS responds. If this direct current flows for a predetermined time, for example JO s, then there is an abnormal conversation state, which can also be the state of being listened to, and the pointer Z responds. The timing element Z gives a | control command to the connection element A, which connects the warning supply source Q to the warning transmitter W.

It should be possible for the participant to temporarily put the acoustic warning device out of operation, but it is allowed to do so cannot be switched off, namely in the event that the participant is transmitting continuous acoustic signals such as music J50 would like. In this case, too, it would be over the entire transmission time the transmission path is opened, and this would thus correspond to the state of being listened to. The decommissioning is technically caused by a non-latching key T, which causes the fault

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protection circuit AS switches off as long as the participant presses the button.

The loudspeaker LS of the hands-free device can also be used as an acoustic warning device, as shown in FIG. 2 is. This is separated from the control amplifier KV2 via a switching device U and switched to a specific one DC voltage potential V (or an audio frequency oscillator) switched. The potential V can be positive.

The DC crackle caused by switching on the potential can be heard in the loudspeaker. At the same time, the timing element Z could be reset and new by means of this potential to be started. The switch u of the switching device U then goes back to its rest position and is according to the predetermined Duration pressed again.

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Claims (7)

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Stuttgart STANDARD ELECTRICS LORENZ
Aktiengesellschaft H.Wiedmann-10 Claims Ij. Circuit arrangement for protection against eavesdropping in voice-controlled hands-free devices, in particular in telephone sets, in which the microphone is connected to the outgoing four-wire output of a hybrid circuit that can be connected to a subscriber line via its two-wire output via a transmission signal detector and a control amplifier, and the incoming four-wire output of the hybrid circuit via a received signal detector and a further control amplifier with the speakers are connected, and because the signals received by these detectors signals the gain of the variable gain amplifier adjusts in a speech control circuit that raised in response of the transmit signal detector, the gain of lying in the transmission path control amplifier and the gain of lying in the receive automatic gain control amplifier is lowered and vice versa, characterized characterized in that a criterion for connecting a d en subscriber is derived from the requirement of triggering the hands-free device alerting the warning device (S, Z, A, W). 2. Circuit arrangement according to claim 1, characterized in that the control signal is fed to a timing element (Z) which responds when the control signal is absent for a predetermined duration in the Ge sprt-ächs state, that the timing element is connected on the output side to a connecting element (A) and when it is triggered, a warning supply source (Q) by means of the CS / P-Krü - / - 4/26/78 909847/0447 H.Wiemann-10 switching element (A) connects to an acoustic warning device (W). 3. Circuit arrangement according to claim 2, characterized in that the timing element (Z) is preceded by a threshold switch (SS). 4. Circuit arrangement according to claim 2 or claim 3 *, characterized in that the timing element (Z) is preceded by a break contact of a non-latching key (T). 5 · Circuit arrangement according to claim 2, characterized in that a switching device (U) is used as the connecting element which, when not controlled by the timing element (Z), connects the control amplifier (RV2) in the reception path to the loudspeaker (LS) of the hands-free device and which at Activation by the timer (Z) causes the connection of the loudspeaker (LS) with the warning supply source and the resetting of the timer. 6. Circuit arrangement according to one of claims 2 to 5 *, characterized in that an oscillator is used as the warning supply source (Q). 7. Circuit arrangement according to one of claims 2 to 5 » characterized in that a direct voltage (+ V) is used as the warning supply source (Q). 909847/0447