GB2231238A - Attenuating audio source during car telephone operation - Google Patents

Abstract

Apparatus to be operatively connected between a cellular telephone installed within a vehicle and a radio or like speaker also installed within the vehicle, which includes means to attenuate the sound level from the speaker upon the receipt of a signal that the telephone is receiving or transmitting a call is arranged to increase the sound progressively at the end of the call to the level prevailing before the call so that the driver is not startled by a sudden loud noise. Attenuation may be switched series resistors R23-R27 or (Fig 2) a transistor variably shorting the loudspeaker. <IMAGE>

Description

VEHICLE TELEPHONE APPARATUS The invention relates to apparatus for use with a telephone and in particular to apparatus for use with a so-called cellular telephone installed in a vehicle such as a car.

A vehicle having a cellular telephone usually has a radio and a cassette or compact disc player too. If one of these is on when the telephone rings it is usual to switch off the radio so that the telephone conversation may be carried on at a normal voice level. It is known to provide an accessory comprising a relay which turns off the radio automatically upon receipt of a signal indicative of the transmission or receipt of a telephone call, and which turns the radio on again when the call has finished.

However, the sound is instantaneously returned to the level prevailing before the call. This can be jarring and otherwise unpleasant or even frightening, in which case an accident could occur.

It is one object of the invention to reduce or minimise this problem.

According to one aspect of the invention there is provided apparatus for use within a cellular telephone and a radio speaker or the like, the apparatus including means to mute the sound from the speaker upon receipt of a signal indicating that the telephone is transmitting or receiving a call, the means being arranged to progressively cause or allow or increase the volume of sound from the speaker to the level prevailing before the call upon receipt of a signal that the call has finished.

Because the apparatus increases the volume of sound progressively the driver is not startled by a sudden loud noise. The time period and rate at which the volume is pregoressively returned to the prevailing level may vary widely, but is preferably up to between 2 and 13 seconds and most preferably up to between 5 and 10 seconds.

The apparatus may be installed within the radio or the telephone or be provided as a separate accessory.

In one embodiment, the apparatus comprises a parallel network of resistors of differing values each resistor having a switch means, which network is connected between the output from the radio and the speaker, the switch means being arranged upon receipt of a signal indicating the end of the call to allow the signal from the radio to flow through resistors of progressively smaller values, whereby the level of signal applied to the speaker becomes progressively larger.

Preferably the switch means comprises transistors which are sequentially activated from the output of a ripple counter means.

Preferably the apparatus includes clock means in circuit with the resistors arranged to control the speed at which the sound is restored to the original level.

In another embodiment the apparatus comprises a capacitor which is arranged to be charged up during the call and is arranged to discharge progressively at the end of the call, and thereby allow the sound level to increase progressively.

In order that the invention may be well understood it will now be described by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a circuit diagram of one embodiment of the invention; and Figure 2 shows a circuit diagram of another embodiment of the invention.

As shown in Figure 1, one embodiment of apparatus according to the invention comprises a circuit to be connected between the speaker output of a radio or the like at R and is connected at T to an output from the vehicle telephone. The circuit is arranged to mute the sound from the radio speaker upon receipt or transmission of a call by the telephone and upon the end of that call to progressively enable the speaker so that the sound increases slowly back to the prevailing level so as not to startle the driver.

The circuit is connected at T to a mute output of a telephone which places a high on that line upon receipt or transmission of a call. The line T is connected via resistor R1 to the base of transistor TR1. The collector of TR1 is connected via both inputs of a dual input Nand gate Nl to the reset pin RST of a Ripple counter RC1.

A clock for the counter RC1 is provided by a resistor capacitor network R3C1 and is connected through one input of another nand gate N3 to the clock pin CIK of the counter Roc1. The counter RC1 uses six of its outputs Q1 to Q6. Each output Q1 to Q6 is connected via a respective exclusive NOR gate El to E6 and Resistor R4 to R9 to the base of a respective transistor TR2 to TR7, whose emitter is connected to ground. The collector of each of the transistors TR2 to TR7 is connected to the junction between two resistors R10 to R22. Each pair of resistors are connected in parallel to a 24 volt line 24v.The 24 volt line is connected via the resistors R10 to R22 to the bases of six pairs of parallel arranged field effect transistors TR8 to TR19.

The six pairs of field effect transistors TR8 to TRl9 are arranged in a ladder-type network L between the radio at R and the speaker at S. Although as shown a single radio output is connected to a single speaker S, there may be one ladder network for each radio to speaker connection, e.g. four. Alternatively four such connections may be connected through the same ladder network L. The collector - emitter connection of five of the pairs of transistors TR8 to TR17 is connected in series with a resistor R23 to R27, each resistor being lower in value than the one above. The sixth pair of transistors TRlS and TRl9 are connected directly between R and S with no resistor being present.

The sixth output Q6 is connected from the clock RCI through a nand gate N4 to one input of nand gate N3, the other input being connected to the clock, Nand gate N2, resistor R3 and capacitor Cl.

In use, and in the absence of any transmission by the telephone, each of the outputs Q1 to Q6 is held high and the base of the transistors TR2 to TR7 is held low; the 24 volt line 24v is thus connected to the bases of the six pairs of transistors TR8 to TRl9. Conduction therefore occurs between the Radio at R through the unimpeded path at O to the speaker at S. The volume of sound is not changed by the circuit.

When the telephone receives a call, a high appears on line T.

The collector emitter circuit of TR1 therefore conducts to ground and a low is applied to the input of nand gate N1, which therefore applies a high to the reset pin RST of the counter Roc1.

The outputs on Q1 to Q6 are reset to low.

The bases of transistors TR2 to TR7 therefore go high so that the +24v is connected to ground through transistors TR2 to TR7.

Transistors TRS to TRl9 cease conducting and the connection between R and S is broken. The speakers are silenced and remain in that state while T and the reset pin RST are held high. At the end of transmission the line at T returns to low so that the clock can start counting again to sequentially apply a high to each output Q1 to Q6 in time with the clock. The first clock pulse or high at Q1 prevents transistors TR2 from conducting so that +24 volts is reapplied to the bases of transistors TR8 and TR9 which thereby conduct and allow the radio signal to flow through resistor R24 to the speaker. However, resistor R23 is of a relatively large value, so that most of the signal is lost across the resistor R23 and the sound from the speaker is of low volume. The next clock pulse at Q2 allows the radio signal to flow through R24, of lower value than R23, so that the volume increases. This occurs in time with the clock pulses until transistor pair TR18 and TRl9 conduct and the signal flows unimpeded through 0 to the speaker S and the volume is returned to the prevailing level. Simultaneously the high on the input of N4 causes a low on one of the inputs to N3 which means that the clock input on RC1 is held low, so that the high level on Q1 to Q6 remain until the telephone is used again.

The time over which the sound level returns to the prevailing level is determined by the speed of the clock and by the relative values of the resistor R3 and capacitor C1 and is preferably about 5 seconds.

The apparatus shown in Figure 2 comprises a +5v line T to be connected to a muting output line from the telephone, a line S to be connected to the positive terminal of a speaker and a 12 volt supply line +12v. The line T is connected via a diode D100 and a resistor R100 to the base of a transistor TR100, whose collector is connected to the +12v supply line via a resistor R400. The emitter of transistor TR100 is connected to earth via resistor R300, and to a diode D200. A capacitor C100 is connected between the other side of the diode D200 and earth. The positive plate of capacitor C100 is connected via resistor R200 to the base of another transistor TR200 whose collector emitter path is connected between the speaker line at S, and earth.

In use, and in the absence of a call, the line S is not connected to earth. The receipt or transmission of a call causes a +5v to appear on line T which biases transistor TR100 and allows a 12 volt charge to appear between the emitter of TR100 and earth.

The +12 volt charge biases the base of transistor TR200 and allows line S to be taken to earth through the collector emitter path of TR200, thereby silencing the speaker (not shown) on line S. The capacitor C100 is simultaneously charged up. At the end of the call line T returns to ground and the +12 volt supply is thereby disconnected from the emitter side of transistor TR100.

However, the 12 volt charge on the capacitor C100 leaks away through resistor R200 at a rate determined by the relative values of the two components C100, R200 and the bias on the base of TR200 falls away progressively, so that conduction of the collector emitter path reduces progressively. In this way, the signal applied to the speaker at S increases and the volume of sound therefrom increases progressively to the level prevailing before the call. In the embodiment shown the values of the components C100 R200 are chosen so that the sound level returns progressively over a period of time of about 8 seconds.

Claims (8)

1. Apparatus to be operatively connected to a cellular telephone installed within a vehicle and to a speaker of a radio or the like also installed within the vehicle, the apparatus including means to mute the sound from the speaker upon receipt of a signal indicating that the telephone is transmitting or receiving a call characterised in that the means are arranged to cause or allow the volume of sound from the speaker to increase progressively over a predetermined period of time to the level prevailing before the call upon receipt of a signal that the call has ended.

2. Apparatus according to Claim 1 characterised in that the means are arranged to progressively increase the volume over a period of at least about 2 seconds.

3. Apparatus according to Claim 2 characterised in that the means are arranged to progressively increase the volume over a period of between 5 and 10 seconds.

4. Apparatus according to any preceding Claim characterised in that the means comprises a parallel network of a plurality of resistors of differing values (R23-R27), and switch means (TR2-TR19), the network to be connected between an output from the radio (R) and a speaker (S), the switch means (TR2 TR19) being arranged upon receipt of a signal indicating the end of the call to allow the signal from the radio to flow through resistors of progressively smaller values, whereby the level of signal applied to the speaker becomes progressively larger.

5. Apparatus according to Claim 4 characterised in that the switch means comprises a plurality of transistors (TR2-TR19) each connected to a resistor (R23-R27) and which are sequentially activated from an output (Q1-Q6) of a ripple counter means (RC1).

6. Apparatus according to Claim 4 or 5 characterised by clock means (C1, R3, N2, N3) in circuit with the ripple counter RC1 and arranged to control the speed at which the sound is returned to the prevailing level.

7. Apparatus according to any of Claims 1 to 3 characterised in that the means of the apparatus comprises a capacitor (C100) which is arranged to be charged up during the call and is arranged to discharge progressively at the end of the call, and thereby allow the sound level to progressively return to the prevailing level.

8. Apparatus according to Claim 7 characterised in that the apparatus includes a transistor (sir200), whose emitter collector path is arranged to be connected between a positive speaker. terminal (S) and earth, the arrival of a signal indicating the receipt or transmission of a telephone call being arranged to bias the base of the transistor (TR200) and to allow the positive speaker terminal to be taken to ground, the capacitor (C200) being connected between the base of the transistor and ground, whereby at the end of the call the capacitor (C200) discharges and thereby reduces the bias progressively so that the signal applied to the speaker progressively returns to the prevailing level.