Volume control circuit for use in portable telephone or the like

Claim 2

A volume control circuit comprising: amplifier means for amplifying an audio signal; first and second holding means for holding the gain of said amplifier means at a first and a second predetermined value, respectively; condition detector means for producing a condition detect signal by detecting a condition of use of equipment in which said circuit is built in; and switch means for selectively enabling said first and second holding means in response to said condition detect signal.

Claim 3

A volume control circuit as claimed in claim 1, further comprising setting means responsive to said condition detect signal for selectively changing the set values of said first and second holding means.

Claim 4

A volume control circuit as claimed in claim 1, wherein said amplifier means comprises an amplifier which includes an input resistor and a feedback resistor, and wherein said first and second holding means each comprises a variable resistor which is connected in series with said input resistor via said switch means.

Claim 5

A volume control circuit as claimed in claim 1, wherein said condition detector means comprises a plunger which is movable when operated from outside.

Claim 6

A volume control circuit comprising: volume means responsive to a control signal for setting a level of an audio signal at a predetermined value; condition detector means for outputting condition signals each of which is associated with a different one of a plurality of conditions of use of equipment in which said circuit is built; setting means for setting a plurality of predetermined values each of which is associated with a respective one of said plurality of conditions of use; store means for storing said plurality of predetermined values; and control means responsive to any one of said condition signals for reading one of said predetermined values which is associated with said one condition signal out of said stored means and feeding said one predetermined value to said volume means as said control signal.

Claim 7

A volume control circuit comprising: volume means responsive to a control signal for setting a level of an audio signal at a predetermined value; condition detector means for outputting condition signals each of which is associated with a different one of a plurality of conditions of use of equipment in which said circuit is built; setting means for setting a plurality of predetermined values each of which is associated with a respective one of said plurality of conditions of use; store means for storing said plurality of predetermined values; and control means responsive to any one of said condition signals for reading one of said predetermined values which is associated with said one condition signal out of said stored means and feeding said one predetermined value to said volume means as said control signal.

Claim 8

A volume control circuit as claimed in claim 5, wherein said volume means comprises: first means for resistance-dividing said audio signal; and second means responsive to said control signal for changing a ratio of said resistance division.

Claim 9

A volume control circuit as claimed in claim 5, wherein said equipment comprises a vehicle-mounted telephone, and wherein said plurality of conditions of use comprise an onboard use condition and a portable use condition.

Claim 10

A volume control circuit as claimed in claim 7, wherein said condition detector means comprises a reed switch which neighbors a magnet in said onboard condition and opens or closes in response to said magnet.

Claim 11

A volume control circuit as claimed in claim 5, wherein said setting means comprises an up-key and a down-­key each being connected at one end to ground and at the other end to a power source voltage.

Claim 12

A volume control circuit as claimed in claim 5, wherein said stored means comprises a RAM (random access memory).

Claim 13

A volume control circuit as claimed in claim 10, further comprising back-up means for backing up said RAM.

Claim 14

A volume control circuit as claimed in claim 11, wherein said back-up means comprises a super-capacitor.

Claim 15

A volume control circuit comprising: store means for storing sound levels each being associated with a respective one of a plurality of conditions of use of equipment in which said circuit is built; condition detector means for producing a detect signal by detecting any of said conditions of use; means for reading one of said sound levels which is associated with said detect singnal out of said store means and delivering said one sound level as a volume control signal; and volume means responsive to said volume control signal for controlling the level of an audio signal.

Claim 16

A volume control circuit comprising: store means for storing sound levels each being associated with a respective one of a plurality of conditions of use of equipment in which said circuit is built; condition detector means for producing a detect signal by detecting any of said conditions of use; means for reading one of said sound levels which is associated with said detect singnal out of said store means and delivering said one sound level as a volume control signal; and volume means responsive to said volume control signal for controlling the level of an audio signal.

Claim 17

A volume control circuit as claimed in claim 13, further comprising setting means for changing said sound levels which are stored in said store means.

Claim 18

A volume control circuit as claimed in claim 13, wherein said volume means comprises means for resistance-­dividing said audio signal, and means for changing a ratio of said resistance division in response to said volume control signal.

Claim 19

A volume control circuit as claimed in claim 13, wherein said store means comprises a RAM.

Claim 20

A volume control circuit as claimed in claim 16, further comprising back-up means for backing up said RAM.

Claim 21

A volume control circuit as claimed in claim 17, wherein said back-up means comprises a super-capacitor.

Claim 22

A volume control circuit as claimed in claim 13, wherein said equipment comprises a vehicle-mounted telephone, and wherein said plurality of conditions of use comprise an onboard condition and a portable condition.

Claim 23

A volume control circuit as claimed in claim 19, wherein said condition detector means comprises a reed switch which neighbors a magnet in said onboard condition and opens or closes in response to said magnet.

Claim 24

A volume control circuit as claimed in claim 13, wherein said setting means comprises an up-key and a down-key each being connected at one end to ground and at the other end to a power source voltage.

Claim 27

A method as claimed in claim 22, further comprising the step of manually changing said amplification ratios.

Claim 30

A method as claimed in claim 24, further comprising the steps of: detecting a change signal for changing any of said first and second predetermined values; deciding whether said equipment is in said onboard condition or in said portable condition, after said change signal has been detected; when said equipment is in said onboard condition as decided after the detection of said change signal, changing said first predetermined value in associated with said change signal; and when said equipment is in said portable condition as decided after the detection of said change signal, changing said second predetermined value in associated with said change signal.

Claim 31

A method as claimed in claim 24, wherein the step of detecting said change signal comprises the steps of: detecting depression of an up-key; detecting depression of a down-key; outputting, in response to detection of depression of said up-key, a signal incremented by one as said change signal; and outputting, in response to detection of depression of said down-key, a signal decremented by one as said change signal.