Volume control in mobile phones

[Ansuman]

I have used many mobile phones and controlled volume on them but I have never been able to figure out how the volume increases or decreases, i.e, what actually happens in a circuit board or other parts present in the phones when we are controlling the volume which ultimately leads to speakers giving out low or high sounds ??

 

[Simon Bridge]

Welcome to PF;
There are a lot of ways to control volume - even in mobile phones - it usually involves physically changing the value of a resistance in the physical circuit.

The easiest way to do this digitally is to change the path that the current takes through a whole lot of very small resisters in an integrated circuit.

 

[Windadct]

Actually I do not thnkink they are using resistance - too inefficient. I am pretty sure it using all switchmode amplifiers - and it is all controlled digitally.

 

[Mordred]

In cell phones some models use variable current oscillators.
Some however in volume still use potentiometers.

 

[Ansuman]

In cell phones some models use variable current oscillators.
Some however in volume still use potentiometers.

If I am not wrong the potentiometers use variable resistors to change the electrical current going to a speaker, when the resistivity is more the volume is less, i may tend to be wrong, i have just passed 9th and am working on a project to adjust volume in the earphones...

 

[Ansuman]

Welcome to PF;
There are a lot of ways to control volume - even in mobile phones - it usually involves physically changing the value of a resistance in the physical circuit.

The easiest way to do this digitally is to change the path that the current takes through a whole lot of very small resisters in an integrated circuit.

that is how a potentiometer works, right ? i am not sure though

 

[Simon Bridge]

If I am not wrong the potentiometers use variable resistors to change the electrical current going to a speaker, when the resistivity is more the volume is less, i may tend to be wrong, i have just passed 9th and am working on a project to adjust volume in the earphones...

If the speaker is in series with the potentiometer (pot) then that is so, but you can also put the pot in a voltage divider with the speaker in parallel.

Note: "resistivity" is a material property, it is possible for two resistors to have the same resistance and different resistivities (they will have different dimensions).

that is how a potentiometer works, right ? i am not sure though

A pot is usually a continuous band of constant resistivity with a contact point. The distance between the sliding contact and one end of the band determines the resistance.

Digital circuits don't do continuous stuff ... the volume has to correspond to a digital number.

You could imagine a series of resistors R connected by switches so that position 0 connects to the next resistor and position 1 connects to the speakers input rail. The other end of the speaker is grounded.

Lets say there are 4 resistors, then the state of the switches is represented by a 4-bit binary number.
0000 means R_tot=0
0001 means R_tot=R
but so does 0011, 0111, and 1111 (draw the circuit to see why)

0010 means R_tot=2R
0100 means R_tot=3R
1000 means R_tot=4R
... if you want more than 4 volume levels, then use more switches and resistors.

This is far too simple - there are lots of other ways of doing it and actual circuits will be more complicated as well as different between different devices. I'm intending it as an easy-to-understand example of the kind of thinking you need rather than an example of what actually happens in real life.

Be aware that the details of how a particular manufacturer's circuit works may be proprietary information - we can only talk, in general, about what sort of thing gets done.

 

[Ansuman]

If the speaker is in series with the potentiometer (pot) then that is so, but you can also put the pot in a voltage divider with the speaker in parallel.

Note: "resistivity" is a material property, it is possible for two resistors to have the same resistance and different resistivities (they will have different dimensions).

A pot is usually a continuous band of constant resistivity with a contact point. The distance between the sliding contact and one end of the band determines the resistance.

Digital circuits don't do continuous stuff ... the volume has to correspond to a digital number.

You could imagine a series of resistors R connected by switches so that position 0 connects to the next resistor and position 1 connects to the speakers input rail. The other end of the speaker is grounded.

Lets say there are 4 resistors, then the state of the switches is represented by a 4-bit binary number.
0000 means R_tot=0
0001 means R_tot=R
but so does 0011, 0111, and 1111 (draw the circuit to see why)

0010 means R_tot=2R
0100 means R_tot=3R
1000 means R_tot=4R
... if you want more than 4 volume levels, then use more switches and resistors.

This is far too simple - there are lots of other ways of doing it and actual circuits will be more complicated as well as different between different devices. I'm intending it as an easy-to-understand example of the kind of thinking you need rather than an example of what actually happens in real life.

Be aware that the details of how a particular manufacturer's circuit works may be proprietary information - we can only talk, in general, about what sort of thing gets done.

Thank you very much, you really explain well but just one more doubt, the volume of different levels are obtained by connecting different resistors ( by switches) , in my project i want to change the volume by sending an electrical signal ( about 40-100 mW [miliwatts] ), without any manual effort ( in simple terms can electrical signals replace manual switches )can I do so ??

 

[raghav singh]

see there are various ways to control volume but the best way can be explained as follow,,,,
source of production is same hence volume is controlled using amplifiers to increase or decrease the extent of sound ,,we call it as volume

 

[Simon Bridge]

Thank you very much, you really explain well but just one more doubt, the volume of different levels are obtained by connecting different resistors ( by switches) , in my project i want to change the volume by sending an electrical signal ( about 40-100 mW [miliwatts] ),

Well why didn't you say so?

without any manual effort ( in simple terms can electrical signals replace manual switches )can I do so ??

Errrr... you didn't understand: the situation I described before: the switches are not manual.
They would be digital circuits etched into the integrated circuit inside the cell-phone.

In what you describe - the details depend on exactly what you want to do - you could, for eg. just use the current to drive an electric motor that turns the crank-shaft of a pot.

You should have a look at your amplifier circuit - what part of the circuit controls the volume?
Replace that with something that changes electronically.
But the short answer is "yes", you can get an electronic signal to set the volume level.

 

[Ansuman]

Well why didn't you say so?
Errrr... you didn't understand: the situation I described before: the switches are not manual.
They would be digital circuits etched into the integrated circuit inside the cell-phone.

In what you describe - the details depend on exactly what you want to do - you could, for eg. just use the current to drive an electric motor that turns the crank-shaft of a pot.

You should have a look at your amplifier circuit - what part of the circuit controls the volume?
Replace that with something that changes electronically.
But the short answer is "yes", you can get an electronic signal to set the volume level.

Thank you very much. I really appreciate your help...

 

[carlgrace]

Thank you very much. I really appreciate your help...

FYI, virtually all cellphone audio amps are using class-D amplifiers these days...

http://en.wikipedia.org/wiki/Class-D_amplifier