DIY Vera Connected Volume Knob

[naveen]

I think what I'm trying to do is fairly straight forward, but I just wanted to confirm everything makes sense.

Briefly, I'm trying to digitally control the volume of my zone 2 speakers (which is a cheap Creative 5200 speaker system from many many years ago). I want to be able to control it from a remote/vera without having to physically change the volume. Currently, the volume knob is connected by a cable that also control the front/rear balance, and the volume knob also click 'on' when you start turning it.

I can't really get the pot off the board without breaking it (I think), it all seems pretty well jammed together and I don't want to destroy the speakers. I'm thinking of wiring up the pots in parallel, and based on my high school electronics I think this makes sense:

R1 = volume knob (assume 5k)
R2 = digital pot (assume 25k)

If I get a digital pot which is much higher resistance than the volume knob, I think the following will work:

Rt = (1/R1 + 1/R2)^-1

If R1 is max (5000) and R2 is max (25000) the overall resistance is: 4200k which is almost the max volume?

And then if I lower either potentiometer I should lower the volume, so I maintain both analog and digital control.

This will all be wired through an arduino/vera to get the automated control I'm looking for .

Please let me know if this makes sense or if there is another way I should probably go about doing this. Thanks!

[BulldogLowell]

@naveen

Whilst you can certainly experiment with this, IMO it may prove to be too cumbersome to get what you want; perhaps having to adjust the other pot to its max each time you 'switch' control.

your example works for both pots at their max resistance but I think your issue will be as one of the pots resistance approaches zero, you may not be able to get enough gain from the other resistor.

think about your formula (in this alternate configuration for just two resistors in parallel) as the value of R1 approaches zero. No matter how big R2 is, its product with R1 becomes a very small number.

[naveen]

@BulldogLowell

Thanks for the response. What you're saying definitely makes sense, but I'm hoping to rarely have to touch the analog/physical pot and do most of the controlling digitally (and leave the analog pot on max resistance). Ideally I could disconnect the analog pot entirely, but that may be more difficult to do without breaking the current volume meter.

[BulldogLowell]

@naveen

I'd look to make the stereo's potentiometer an input to arduino. Then you can put logic in to:

determine which 'wins' in the volume battle
lockout the other for some period if an adjustment was just made on one
perhaps use the manual knob as the max volume setting...

there may be lots more you can do if you have two inputs to your arduino.

[naveen]

@BulldogLowell

I wouldn't be opposed to disconnecting the volume knob entirely, but I can't get the PCB off of the knob to remove it. But I can access the bottom of the PCB so I was thinking of just soldering the new pot in parallel (for ease). Ideally I'd be able to remove the original pot.

[BulldogLowell]

@naveen said:

@BulldogLowell

I wouldn't be opposed to disconnecting the volume knob entirely, but I can't get the PCB off of the knob to remove it. But I can access the bottom of the PCB so I was thinking of just soldering the new pot in parallel (for ease). Ideally I'd be able to remove the original pot.

is there room for a servo? That would be cool, plus you wouldn't have to re-do the taper on the existing pot.

[naveen]

@BulldogLowell

Hmm, that's not a bad idea actually. A bit bulkier of a solution but may be easier that dealing with the pots. Thanks for the suggestion!

[naveen]

@BulldogLowell

Can a servo report its current position??

[BulldogLowell]

@naveen

there are two kinds (maybe more)

one lets you control its precise rotation zero to 180 degrees (what you want) and another that does continuous rotation.

[gregl]

Cool project!

Just to chuck in some other ideas...

• Replace existing pot ( is it stereo? ) with http://arduino.cc/en/Tutorial/SPIDigitalPot
  https://www.sparkfun.com/products/10613

• Replace existing pot with a motorised one..http://www.ebay.com/itm/ALPS-Remote-Motor-Volume-Potentiometer-Control-Adjustment-4CH-50KA/321428122915 ( or similar)

• you could probably salvage one of these from an old stereo system...many in the late 80's /90''s had these....

Good thread here:
http://forum.arduino.cc/index.php?topic=143271.0

Keep us posted!

[naveen]

@gregl said:

Cool project!

Just to chuck in some other ideas...

• Replace existing pot ( is it stereo? ) with http://arduino.cc/en/Tutorial/SPIDigitalPot
  https://www.sparkfun.com/products/10613

• Replace existing pot with a motorised one..http://www.ebay.com/itm/ALPS-Remote-Motor-Volume-Potentiometer-Control-Adjustment-4CH-50KA/321428122915 ( or similar)

• you could probably salvage one of these from an old stereo system...many in the late 80's /90''s had these....

Good thread here:
http://forum.arduino.cc/index.php?topic=143271.0

Keep us posted!

Thanks for the ideas! Replacing the existing pot is probably the simplest thing and what my original plan was...until I realized that the knob and board don't come apart.

WAF-wise I don't want this thing to be unusable for the foreseeable future.

I think I'm still leaning towards the pot in parallel (for its simplicity) or the servo....but the servo will be quite bulky to the little switch!

I'll post some pictures when I get a chance to clear up what exactly I'm trying to do