Digital volume remeber settings? please help

[stuee]

I found this schematic but i want it for my car, i will make 4 of them, one for front speakers, back speakers, 1 sub and other sub, but the problem is when the power is off it forgets the setting, i want it to be able to rememebr the settings without having the whole car ignition left on.
Any help most greatful, thanks

Schematic herehttp://www.aaroncake.net/circuits/volume.htm

[audioguru]

Stuee,
The DS1669 digital pot has memory built-in, so you can turn off its power and it will come back-on the same, but it updates its memory only if a change of 8 steps or more is made.
The project that you referred has an error: the supply voltage is +,- 4V maximum, not +,- 5V. Your inputs may need attenuation so that they do not exceed 8V p-p. You need a -4V supply converter, unless the top end of the pot is biased at +4V and the bottom is capacitor-coupled to ground, using a +8V supply. The DS1669 data sheet is here:
http://pdfserv.maxim-ic.com/en/ds/DS1669.pdf
Have you considered the application of this linear-steps control for a logarithmic volume control? Therefore over this 64-step control, the top 10 steps will hardly make any difference in the volume, then turning it down further the steps will become broader and broader, until near the bottom they will be coarse. The difference in volume between maximum and half-way (32 steps) is noticeable but certainly not half-volume. If the volume is much too loud when you turn it on, then it takes a number of seconds to reduce it even on "fast" mode. That will seem like a long wait if it's blasting.
But there is a way of "loading" the slider so that it is not that bad.
How are you going to control the amps in unison? By using 4-pole buttons?
How are you going to display the volume setting?

[stuee]

my idea is to take it from the volume ctrl pot on the amps for each setting, rear, front, amp2 rear, front, im not a big electronic guru, i can read circuits and build them but that as almost my lmits thats why im on here :D

I would like a volume control display, also would be good if only had 3 buttons, one to select the audio chan, and the other 2 for changing the volume, not sure how easy that is,

and is there a schematic for a 12v to 5v converter anywhere?
Thanks for your help so far.

[audioguru]

Stuee,
You cannot simply apply power and audio to the device as the project's author implies. If you do, then the audio will cause the voltage of the resistor element to swing up and down, exceeding the absolute maximum negative voltage rating of the element (-0.5V), which will cause severe audio clipping and may damage the device.
In the author's Note #4, he advises to use a +,- 5V supply to solve this problem, but that is also an error since it would exceed the absolute maximum supply voltage of 8V for the device. He also failed to mention attenuating the input so that it doesn't exceed its rating.

That is why I mentioned biasing the pot and cap-coupling one end to ground when using a +8V supply, or using a +,- 4V supply.
It is difficult to make a quiet +,- 4V supply from a car battery, but it is easy to make a +8V supply from an LM317, then bias and cap-couple the element.

I must correct my statement about biasing and cap-coupling:
1) Bias the LOW end of the element to +4V, by using an equal-valued-resistors voltage divider of the supply voltage. Capacitive-couple the +4V to ground, so that audio is completely filtered out.
2) Attenuate the audio source so that it does not exceed 8V p-p.
3) Capacitive-couple the attenuated audio source to the HIGH end of the element.
4) Capacitive-couple the element's slider to your amp's input, or make certain that your amp has an input capacitor.

If this element is the same value as the existing volume control, then when paralleled the combination will double the source's low cutoff frequency.

How do you feel about the step sizes changing with volume setting, which makes the steps crammed together at the high end, and spread out at the low end?
Some day, maybe someone will make an audio digital pot.

[stuee]

ok here is my idea, not sure how to put it all together, and what parts to use, if someone has a idea and would help me design this i would me most greatful and also post it one here when completed for others to use too.

Below is my idea how it sould be.
1= line in from amp analoge pot. front speakers
2= line in from amp analoge pot. rear speakers
3= line in from amp analoge pot. Subwoofer 1
4= line in from amp analoue pot. Subwoofer 2
5= Line Selector button, Pref with display so i can see what line im choosing.
6= volume up button
7= volume down button
8= lines from selector to vol controlers.

Ok. the lines from the pots on the amps are single gain lines, if it is possible to connect th signals from the amps to a chip that selects a line the sends it to the volume controlers, as only one line will be in power at once, i should be ablt to use onely one set of up / down buttons.

Ok hope this makes sense, and remember im s dumb electronics person so u might want to explain more detail :D
Thanks
8=