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Old 25th October 2005, 11:34 AM   #111
float is offline float  England
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Hi Russ, just wondering if one pot and one PIC could control say three PGA chips for a six channel volume control. Might be useful for the digital active crossover crowd (maybe me one day )???
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Old 25th October 2005, 11:54 AM   #112
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Quote:
Originally posted by float
Hi Russ, just wondering if one pot and one PIC could control say three PGA chips for a six channel volume control. Might be useful for the digital active crossover crowd (maybe me one day )???

Well, the short anwser is yes, if you added one more control to the select the channel to be adjusted... but, I would not implement it as such.

If I were to try it, I would do it as I have with the 5.1 pre I am working on, and use a push-in switch type rotary encoder.

One cool thing about the kookaburra PCB though is it would be very simple to control one or more kookaburras from an external controller board, and you could do it several ways. You could simply omit the PIC and run wires to an external PIC through a header or something, or you could leave the PIC on the kookaburra, an run a 3 wire cable from the pot header to a digitally controlled analog pot. Maxim has a ton of those type pots to choose from.

The first give you the most flexibility, as you could control two channels independantly.

You could even tap the "SO" pin from the PGA2311 on one PCB and wire it to the "SIN" pin of the PGA2311 on another PCB and then join DGND, SCLK,and CS as well, then you for a large shift register and could control N number of channels, but you would need to rewrite the PIC code to handle that. You would also want to use a rotory encoder/remote reciever or something as I mentioned earlier to get the input from the user.

Pheeeew that is hard to explain quickly, I prolly completely botched it up.

Cheers!
Russ
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Old 25th October 2005, 12:08 PM   #113
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Quote:
Originally posted by Russ White



Well, the short anwser is yes, if you added one more control to the select the channel to be adjusted... but, I would not implement it as such.

If I were to try it, I would do it as I have with the 5.1 pre I am working on, and use a push-in switch type rotary encoder. Cheers!
Russ
Rotary encoders are comparatively expensive -- for a darkroom controller I built I used pushbutton "up" and "down" -- with a routine that accelerated the increments the longer the button was held.

Of course, you can make it overly complex like the clock in my new car -- it requires a master's degree from Carnegie Mellon to program the darned thing.
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Old 25th October 2005, 12:15 PM   #114
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True, a lot of rottary encoders can be expensive, especially the optical ones. I found a pretty good mechanical one for about $4US though, and it is working great, and thats really less then some quality pots.

Push buttons are certainly another excellent option.

That reminds me....

One feature I added to the code for the Kookaburra is a turn on "ramp up" time about about 3-4 seconds. So, the volume comes up to the current setting on a curve, so if you left it on full tilt when you turned the preamp off and forgot, or your child turn the knob completely clockwise... when you turn the thing back on you won't be as likely to blow a speaker, or an eardum.

Cheers!
Russ
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Old 25th October 2005, 12:17 PM   #115
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We are looking at a rotary encoder in the $3-4 range, designed for car radios and nav systems. Another nice thing about the encoder is that it's easy to integrate into your front panel without a lot of machining. Buttons are easy too, but it's hard to find ones that aren't ugly.

We are also designing a touch-sensitive interface for the source selector, but it could be used for other applications as well, such as up/down volume control. It will use QProx chips. Very simple and inexpensive to do.
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Old 25th October 2005, 01:46 PM   #116
float is offline float  England
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Quote:
Originally posted by Russ White



Well, the short anwser is yes, if you added one more control to the select the channel to be adjusted...

I was actually just hoping 3 wires from the pic to three PGA chips would be an accurate six-gang pot. I wasn't thinking of balance adjustments between channels, if thats what you're referring to .

I can tell I'm out of my depth here.......
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Old 25th October 2005, 02:18 PM   #117
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Quote:
Originally posted by float

I was actually just hoping 3 wires from the pic to three PGA chips would be an accurate six-gang pot.
Oh sure you could indeed do that if you could find a 6-gang pot. Not sure I have ever seen one, but that does not mean they don't exist.
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Old 25th October 2005, 02:35 PM   #118
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If you wanted them all to have the same volume, one other easy thing to do would be to take 3 PCBs and have them all share a common digital PS.

Notice the pot header has +5V, WIPER, and DGND pads.

So you would omit JG and R1 on the 2 "SLAVE" boards. You would then run a wire from the +5V pad on the "MASTER" PCB to the +5V pad on each "SLAVE" PCB. And you would likewise run a wire from DGND on the "MASTER" PCB to the DGND of each "SLAVE" PCB.

Then you would take the 3 wire cable from the "MASTER" PCB to a singal 5K linear pot. You would then run a single wire from the "WIPER" pad on the "MASTER" PCB to the "WIPER" pad on each of the "SLAVE" PCBS leavbing the other to pads empty. Then all 3 PCBs will use the same volume pot, and will have the same volume setting.

The easier way to do that would be that when you make your 3 wire connector for the POT header, you use two wires for each PIN(5V,wiper,GND), would would then put a second connector on one set, and the other set you would run to the POT. You could thus "daisy chain" the boards together, the important thing is that they all share a common PS, so omiting R1 and JG is important for the slave boards.

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Old 25th October 2005, 02:59 PM   #119
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Ok one further thought, but maybe this is way over the line. But hey I am having fun.

You run a master pot from one PCB, and run the wiper of that pot to one end of a seperate additional pot on each PCB with the other end of each of those pots being GND. Then you should adjust the level of each PCB individually relative to eachother, but they would all go up and down with the "master" pot.

If you parelleled the output of each PCB you could run 6 PCBs for truly independant 5.1 audio.

A little far fetched, but it would work!

If you were not interested in left/right adjustments you could actually do it with just 4 PCBs, one for LF/RF one for LS/RS and one parallel for Center and one paralelled for SW.

Maybe I should try to illustrate that....

:EDIT: clarified a bit
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Old 25th October 2005, 03:10 PM   #120
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Quote:
Originally posted by Russ White
But hey I am having fun.

Maybe I should try to illustrate that....
While your having fun.....

Try designing it! I'd buy one!

Also couldn't you get away with 3 brds if you put the center on one channel and the sub on the other? Since MOST subs have level controls built in...
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