Logic puzzle: Same 3 pots for 3 discrete boards - demultiplexer?

[jubal81]

I'm trying to figure out the best way to select three different boards (one active at a time), but use the same three pots to control each.
My research has led me to demultiplexer chips (complex CMOS chips that take 4 signals and rout them to lots of different places, so one for each pot?).
Ideally, I'd like to use a rotary switch to choose the board and another switch (possibly using 3 simple 4053s like in RG's design) to engage/disengage the pots.
Anyone done anything like this or have an idea if or how it would work?

[crane]

This could be done in many ways - each of them having their own advantages/disadvantages.
I think that there is no best way - it really depends on build aspects  - If there are long wires from pots to PCB - I would choose to use FETs or optocouplers straight at the lugs of the pots.
If wires are short - FET switching (no matter if it's discrete FET's, analog switch ICs or analog demultiplexers) or optocouplers on pcb.
Recently I really like to use optocouplers for many kind of things - it allows to isolate digital control from audio path. DIY vactrol with an LDR and LED costs <1euro.

[jubal81]

I hadn't even thought about optocouplers. Great idea.

[earthtonesaudio]

I have a feeling physically switching the pots in and out of the different circuits would cause some popping problems.  I'd go for optocouplers or digi-pots.  Either of those can stay connected to their respective circuits all the time.  Then it's just a matter of selecting one of three effects to hear.

[toneman]

use pots to control the voltage(s).
use voltage(s) to control opto(s).
then U can multiplex the pots.
or........
use voltage controlled circuits.
then U can multiplex control voltages to the circuits like the knobs on the Paia Proteus monosynth.
U can even store them in memory if U digitize them to binary first.

a LOT of work to eliminate some $1 pots 

[jubal81]

OK, I think I might have come up with a scheme to do this.
The idea is to make a circuit board with multiple opto 'pots' using a design like the Rock 'n Control: http://tech.thetonegod.com/rockncontrol/rock.html
The voltage comes in, goes through a CLR, then goes through the pot. After the pot, the current goes to the first 'optopot' and daisy chains to the rest, each calibrated to different resistances.

Here's my cheesy hand-drawn diagram:



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[toneman]

"opto pots" 

CLR     Current Limiting Resistor  Probably not
Maybe U mean, LCR, Light Controlled Resitor, or LDR, Light Dependent Resistor.
I think, based on the item at the top of the page, U mean LDR 

Don't understand what all the "3's" are 
Or do U mean "}"     "parenthesis"

Do U want each pot to control 3 LDR's 
And, U have 9 LDR's and 3 pots 

Or, maybe....ONE LDR (at the top), and ....wait, maybe I should look at the "rock-n-control" link...
....(jeopardy theme playing in background).....

Hmmmm.....

The variable resistor symbol (top of the page), could also be an LDR, goes to "nine boxes".
If each of them is an LED, and all are in series, don't think U can do this with 9V, since each LED is about 2V.
Kind of understand ......then......maybe not.....
sorry 

[jubal81]

I had a feeling by diagram might be more confusing than helpful.
I did mean CLR. One of them to keep the LEDs from burning out if the control pot is turned down. It's in series with the voltage line right where the power comes in.

Also, the circuits aren't even close to being drawn realistically. I just scribbled a few optocoupler pairs and transistors on there to help me think about how many parts I was going to need.

There is only one real pot in the drawing. It's at the top. The basic idea is that the pot puts resistance in the voltage line to vary the brightness of the LEDs all at once.

I guess instead of 'optopots' I should have used the analogy that I'm trying to design one 9-gang pot.

I'll have as much as 23 volts available to tap into, but it never occurred to me that 9 volts wouldn't be able to light 10 LEDs. I've seen a couple AA batteries light up a whole lot more than that.

[egasimus]

toneman, pls attmt 2 rite nrmly. kthxbye.

The '3's confuse me too, though.
As for powering those optos - those AAs can light up a lot of LEDs because the LEDs are wired in parallel. You should look up what is the voltage drop for the LEDs in your optos. If it's 3V or a little less, you can connect 3 series chains of 3 LEDs each, and connect those 3 chains in parallel... I hope this makes sense, and, if not, look here.

This is one way to do things. Another is going all voltage-controlled, as has been suggested. You can start from here, where our beloved R.G. has given us the lowdown on different methods for voltage control. I think FETs would be the best option in your case, although I've yet to try any of those methods.

[earthtonesaudio]

It would help to know what 3 circuits you want to control.  For example, if each circuit has a volume pot with one lug grounded, that can simplify the solution.

[EATyourGuitar]

@crane, are you the famous crane song? love the gear, top notch stuff.

[jubal81]

It would help to know what 3 circuits you want to control.  For example, if each circuit has a volume pot with one lug grounded, that can simplify the solution.

Yeah, I wish it were a matter of just needing a variable resistor, but these are going to be tone stacks and the ones I'd like to use all need variable voltage dividers.

EDIT: lol, those aren't 3s. They're my squiggles to represent the LDR. Each board will need 2, with 2 transistors and some resistors.