Storing Pot values (using one pot for multiple parameters)

[itsmedant]

Hello everyone, Just wanted to thank everyone who is a part of this forum, there are boatloads of info on here!

So first off, I'm new to the whole effects building, in fact, I'm new to building anything electronic! I have no background in electronics so I'm starting from ground zero. I've done a lot of research and I will be attempting a fuzz pedal this weekend (gotta do some college work before I get to play!)

hopefully all the research I've done pays off and I can make it with little to no mistakes (fingers crossed)

But I digress, that's not the point of this topic. I had an idea the other day with a fellow coworker to try and have a wah style pot control more than one parameter (volume, tone, speed, ect) and to be able to switch between each one with a footswitch. Applications could be to be able to increase speed of tremolo without having to reach down and turn a pot but to be able to do it with a rocker style pedal by foot.

I don't know if there would be a way to store the resistance value that you end on with the rocker, then change to another parameter like volume and change the position of the wah pot. What I've learned so far tells me that this is impossible with just one pot because that pot actually changes the resistance of the line when it is physically moved.

Is there a way to somehow store this level of resistance and have it remain there until the parameter is selected again?

Thanks ahead of time and I hope to learn even more from everyone here!

[Hides-His-Eyes]

If i were you, I'd start small, build a Bazz Fuss, start to get interested in this kind of thing, try out some other circuits, learn what makes them tick...


Then in 2 years time when you're really good- THEN this will be a really interesting project to look into...

[mth5044]

Sounds like digital territory. Perhaps look into an arduino?

[tiges_ tendres]

Sounds like digital territory. Perhaps look into an arduino?

Yep, my thoughts exactly.  I would imagine some kind of digi-pot, but then you would have to tell the Arduino the code for how you want to implement the whole keep set value until I move you thing.

Hmmm...

[01370022]

To tie those answers together; Yes, it is possible. It is also quite complex. And as a self admitted newbie, take the advice of starting small and don't worry if you're either A:feeling stupid or more likely B:feeling "that's not what I asked for".

Your project as stated will need an in-depth knowledge of the circuit in question, including what each circuit block (the broken-down parts of the circuit) does and how to manipulate the values of components involved to get the output you want, you will also need some degree of switching knowledge to handle the switching side of things.

Also as mentioned in earlier posts, to do this you will have to enter the digital realm, so you will need to make an informed choice of what chip is best for the job along with a decent knowledge of how to program said microchip. To cap it all off you will need a working knowledge of analogue/digital interfacing. What I have listed is probably the basics and I may've left something out since I can't do digital programming.

I'm not trying to put you off, just make you aware of the scale of the learning curve you have ahead of you. It will take you some time to learn this knowledge, and that's why people recommended that you produce a fuzz box where you can learn the basics of audio electronics. Plus, by it branches off into other areas that you will find interesting that you may have never thought of before

Good luck dude and let us know what you end up doing 

[amptramp]

It sounds like what you are looking for is an analog-to-digital converter that permits the pot rotation to be stored as a digital value in a register.  The register can be read and run through a digital-to-analog converter for each controlled parameter.  Many simple converters use R-2R switching and can be used as a pot.  One problem you may run into is the precision necessary for log or audio taper pots, typically used as level or volume controls.  The resistance change is logarithmic with rotation, meaning you may need a fair bit of precision.

You do not have to program a microprocessor to perform this function.  This can be done with logic gates and registers, but a PIC series microprocessor may be smaller and cheaper.  For each performance selection, you can set up an individual register number that corresponds to all the pot settings for a particular song.  Say, register setting 5 may contain the fuzz parameters for "Satisfaction" and you can set up a couple of stomp switches to select the setting.  (I recommend an up and down select switch for parameters as you may change the order in which you play various songs and you don't want to be futzing about on stage with just a single control.)

You will find people on this board with interest but no education in electronics, informal or otherwise and you will also find electrical engineers.  Find yourself a good text on the electronics and start the process of learning.  It's like playing music - once you get good, it gets fun!

[itsmedant]

thanks everyone!!

I was thinking that there would have to be something digital in there. Just wanted to know if I was thinking this right or not.

And yes, I know this may be a little out of my skill box but this is not something that I am going to try right now. I just got the fuzz kit from smallbear to learn about the different parts of the schematic and how to tweak and play around with values.

Also got the pcb board kit from them so once I get a grasp of what I'm doing on the bread board I'll try my hand at making a pcb for what i have created on the bread.

I was on my way to being an engineer then I realized I really suck at calculus! Now I'm a business major and I need and interesting hobby (cause those classes are booorrrrriiinnnggggg)

[GibsonGM]

The answer is easy:  just calculate the indefinite integral from 1 to 'expert stompbox builder', and you'll have the answer!!   ) Just kidding; it is a difficult proposition, but someday you may get there (in digital, of course).    Enjoy getting started, welcome to the forum! 

[Tony Forestiere]

The answer is easy:  just calculate the indefinite integral from 1 to 'expert stompbox builder', and you'll have the answer!!   Shocked) Just kidding; it is a difficult proposition, but someday you may get there (in digital, of course).    Enjoy getting started, welcome to the forum!

Now you are treading on the Wonder axiom to the Heisenberg Uncertainty Principle.

[Hides-His-Eyes]

If anyone has any fun maths problems involving parallel logarithmic pots just let me know, i love that stuff

[itsmedant]

The answer is easy:  just calculate the indefinite integral from 1 to 'expert stompbox builder', and you'll have the answer!!   Shocked) Just kidding; it is a difficult proposition, but someday you may get there (in digital, of course).    Enjoy getting started, welcome to the forum!

Now you are treading on the Wonder axiom to the Heisenberg Uncertainty Principle.

alright now i'm lost. 

I'm so tempted to stop studying tonight and just try and print my first pc board.....I have everything ready for it too, but I know that if i start doing it, I'll be up to 2-3am working on the pedal and I gotta get some good sleep tonight, have an exam tomorrow morning! This weekend I'll have some time to myself to give it a go. I plan on building the entire thing on a breadboard, even though I know the schem is perfect and will work, still wanna see what i'm doing as far as testing certain areas and watching how it all goes together. Then I'll make the pcb and start transfering everything over.

This seems like the most recommended processes on this forum for the beginner builder.  (i'm becoming a semi-pro in the search feature on here!)


I finished painting the enclosure the other day and it turned out amazing! But when trying the dark t-shirt transfer method, my iron melted a part of the paint so I have to redo it. And I also think I may need to spray the pedal white right after the primer, the lighter colors got alot darker after I baked them and my bright orange and neon green turned into a baby food brown and camo green lol. I also think I need a different clear coat than what I got. It doesn't seem to coat the pedal like the actual paint does, just gives the pedal a sheen and strange feel. Any suggestions on type of clear coat to buy? (and can I get it at walmart? hehe)

[PRR]

> a wah style pot control more than one parameter (volume, tone, speed, ect) and to be able to switch between each one with a footswitch.
> would have to be something digital in there.

No, you don't HAVE to go digital. But today a digital solution is "possible", while other approaches are much more work than bending-over.

The great thing about a "pot" is that it is both a control and a "memory". It holds a setting forever, or until you move it again.

But that also means each parameter (volume, tone, speed, ect) needs its OWN "memory".

Therefore multiple pots, or some other multiple storage system which can set resistance or resistance-ratio.

Forget digital. Look inside a wah-type foot pedal. There is a pedal on a shaft (hinge), a toothed rack, and a gear on a pot.

Mount three geared pots side by side. Make a long hinge-shaft for the pedal, so that it can slide side to side. Foot-slide the pedal left, it hits and turns the Volume pot, right it works the speed pot, center works the tone pot.

Well, you need another mechanism to gently lift the tooth-rack off the pot-gear, without a bump, and after side-slide, drop the tooth-rack onto another pot-gear.

I can think of a general plan to do this with "a footswitch".

Look at bicycle derailleur gears. Your foot-pedal can turn gear 1, 2.. 5. On a bike all the gears turn together, but you could slice them to turn different things. Of course a derailleur will NOT work: it has a separate shift-lever, the shifting requires rotation, it does not like to turn both ways, the action is brutal, and bike gears are too close together. Just an example of selecting "what to turn".

Study a classic motorcycle gearbox. When you step on the gears-pedal, you turn a "drum". The rim of this drum has grooves and bumps. These move linkages to disengage 1st gear and engage 2nd gear, etc. Of course a motocycle gearbox won't work: all the gears come out the same shaft, at different ratios, and there's maybe 13 teeth on a gear so "engaging a gear" forces a large jump in shaft position. Anyway a gearbox is bigger than three pedals. But you could carve a similar mechanism from hard wood. You could even mount pots directly on the drum (wires flex) and rotate the desired pot into contact with the wah-linkage. I see hundreds of hours of brain-work and wood-work here.

There are "servo motors". In general, you turn one shaft and electric signals turn another shaft. They were used on radar, bomb-sights, and on wind-direction indicators. They have of course mostly been displaced by LED/LCD readouts.

There is a similar "servo" in R/C model airplanes. You move a knob or joystick on a control box, a servo motor up in the airplane moves the throttle, elevator, rudder, etc. In an airplane you have to control several things at once, so you must have multiple knobs/joysticks. In your application, one knob or pedal plus a connection selection could move one servo (and attached pot) at a time. You don't need the radio part of the system. The servos are cheap. A foot-switch to select more than two connection is not trivial. And the control signals for these servos is a little tricky (optimized for lightweight simplicity). They are normally controlled by a variable width pulse. There are of course chips to generate these pulses from control-box pots; but nobody DIYs control-boxes so it is hard to find clear documentation. The robot-builders also use these servos; in some sense, what you want is a very simple "robot" to turn pots for you.

One nice thing about these semi-mechanical solutions is that you can use an actual "pot". Many digital solutions prefer to drive a "digital potentiometer" which is not the same thing. Inside a guitar-amp, signals on pots can be over 60 Volts; digital pots only take 6V maybe 30V maximum before gross distortion or smoke. This can force complete re-design of the audio gizmo being controlled (and maybe even at 9V pedal-level). The intrinsic audio distortion of a pot can be very low; digi-pots can have "low" distortion but some of the more attractive ones are a bit nasty. Digital pots are always "switches" with 32, 64, sometimes 256 steps, while a pot can in theory have "infinite" settings. We like "taper" pots for a wide range of control; digi-pots are either linear or more complicated.

[itsmedant]

Dang Paul! Heck of an explanation there but it has got me thinking! This project probably won't even get started for a year or so. I have a book of ideas that its written in and notes and additions to it that i'll find along the way. I plan on pumpin out a few other effects before I try something tricky like this.

A mechanical solution was something that has been on my mind the past day or so. Have something like a derailleur for the track to grab the other pots. but then i gotta figure out how to "shift gears" I'm going to bring this idea and some parts to my grandpa (who imo, can build anything) when I go home this summer. He was the one who got me into guitar and building stuff. He has built guitars as a hobby for about 15 yrs now.  Perhaps he will figure out a way to do it!