Want to remotely control potentiometers, not sure how

steambc

Hi Guys,

As a musician, I use two effects pedals each of which has several pots to control various parameters.

While performing, I can't tweak these pots as I would have to bend down to do it. I was thinking that there must be a way to create a "pod" of some kind that I can mount on my mic stand, and each pot on the "pod"·would remotely control a corresponding pot on the pedal.

The actuators connected to the pedal pots would have to be mechanical in nature (as opposed to replacing the pots with electronics), because I would want it to be universal in nature... having the ability to fit the device(s) to any pedal or even an amplifier.

Essentially, if I turn pot 1 on the "pod" to 10:00, I would want the controlled pot to turn to 10:00. The assembly would have to rotate in very fine increments since I would be doing some fine tweaking of the controls for the sake of the overall balance of instruments. I'm basically looking for a 1:1 ratio so I always know how I'm set just by looking at the "pod" pots.

Can any of you steer me in the right direction? I was thinking of using a basic stamp II as a controller, but I also need ideas for the mechanical turning of the pots. Servos? Worm gears? I don't mind inventing something new if nothing exists already.

It absolutely doesn't have to be wireless in any way , unless that turns out to be easier to implement.

Thanks for any and all suggestions. Please respond even if your ideas seem a little outlandish. It's brain-storming time!

Thanks again,
Brian

mikediv

Steam I am not sure I fully understand I get you can not bend over but what about foot pedals ?? even if you have remote pots how are you going to activate them by hand? So it would seem you have to touch or control somehting anyway wouldn't it just be easier to do it with a foot pedal? you could easily rig a foot pedal to control a pot , think of it like a gas pedal the more you push down the more somehting happens . I'm I on the track track?

Mike Green

A servo would do the job. You'd want one that has a suitable range of movement for use with the pot. Use a protractor to measure the range of movement of the pot from mechanical stop to mechanical stop and get a standard servo that's designed to cover the same (or slightly larger) range. The Stamp could measure the pot on the microphone stand using the RCTIME statement and then control the effects pot position using the servo.

Have you looked at the Stomp-1 effects controller that uses a Propeller? In addition to just being a good effects controller, you could easily relocate the controls or even use something different since it's all digitally controlled anyway.

steambc

mikediv said...
Steam I am not sure I fully understand I get you can not bend over but what about foot pedals ?? even if you have remote pots how are you going to activate them by hand? So it would seem you have to touch or control somehting anyway wouldn't it just be easier to do it with a foot pedal? you could easily rig a foot pedal to control a pot , think of it like a gas pedal the more you push down the more somehting happens . I'm I on the track track?

Hi Mike,
The two floor units that I use already have foot pedals, plus a main volume pedal, so the number of foot pedals is getting out of hand.
With a mic-stand mounted unit, I can tweak knobs during a slow part of the performance and also while I'm talking to the audience in-between songs. I could even adjust the gain on my amps with such a system. The single point of focus would be very helpful in seeing how things are set at a quick glance.
Thanks for the input!
Brian

steambc

Mike Green said...
A servo would do the job. You'd want one that has a suitable range of movement for use with the pot. Use a protractor to measure the range of movement of the pot from mechanical stop to mechanical stop and get a standard servo that's designed to cover the same (or slightly larger) range. The Stamp could measure the pot on the microphone stand using the RCTIME statement and then control the effects pot position using the servo.

Have you looked at the Stomp-1 effects controller that uses a Propeller? In addition to just being a good effects controller, you could easily relocate the controls or even use something different since it's all digitally controlled anyway.

Hi Mike G,
That sounds like a good idea. I had a feeling a servo would be the answer. I have a Basic Stamp II mounted on a Board of Education, so I'll study up on reading pots with the rctime statement.
Would this method tend to drift out of calibration easily? Is there some kind of routine where calibration can be maintained in the interest of accuracy?
Finally, do you know offhand of any similar project either on the Parallax site or elsewhere so I don't have to reinvent the wheel? I know Google is my friend, and I will use it; I just thought you might be aware of something that can get me on the right track. I want to make sure I don't miss any resources.
Thanks for your help!
Brian
Edit: I think trying to hack that stomp box would be like opening a Pandora's box for me. Something tells me I should start from scratch.

Mike Green

Both servo motion and RCTIME readings have some "jitter", but they're generally reproducible. In other words, positioning a servo using a particular control pulse width will result in slight differences in end position, but these differences don't accumulate. You may have a couple of degrees of "jitter", but it will always be centered in the same area of the servo's motion. Similarly, if you measure the resistance of a pot using RCTIME, you'll get a little variation, but it won't drift unless there are very large temperature shifts, something you won't see in your application. I don't think you'll find any examples of what you want. It's a very specific application. You'll find lots of general examples in the Robotics with the BoeBot tutorial and at www.emesystems.com following the "app-notes" link and looking under "RCTIME statement".

W9GFO

I think this is over priced, and would be easy to build yourself, but here is its. Seems close to what you want.

www.servocity.com/html/servo_recorder_playback_contro.html

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

steambc

Great information, Mike. This is just what I need to get things going.

Thanks a lot!

Brian

steambc

W9GFO said...
I think this is over priced, and would be easy to build yourself, but here is its. Seems close to what you want.

www.servocity.com/html/servo_recorder_playback_contro.html

Rich H

Rich,
Thanks, that looks interesting but it looks like it will only rotate a servo 180 degrees, unless I can come up with some kind of linkage that would gear up the travel. It seems that most pots have a mechanical range of about 280 degress, give or take.
What about that servo tester in your signature? Wouldn't that accomplish what I'm looking for?
Thanks again,
Brian

W9GFO

My servo tester would control only one servo (well two, but they both receive the same signal) so you would need one for each pot. I don't know of any hobby servos that rotate more than about 180 degrees, except for some winch servos and of course continuous rotation servos.

My first thought would be to try to modify a servo for the extra travel, probably by replacing the existing pot and removing any mechanical stops.

At the extremes you can probably expect a servo to respond to pulses between ~ 500uS and ~ 2,500uS. Depending on what you use to drive the servo that could mean 2,000, 1,000 (Basic Stamp) or even only 200 (some servo testers) possible positions. The dead band of the servo will play an important part too. A standard servo may have a 10 uS dead band while a high end servo may only have 1us of dead band. Obviously, the high end servo will be more accurate. With a Basic Stamp and a standard servo I would think that you could get up to about 200 useful positions out of it - 100 each way, maybe more, maybe less. I don't know if that is fine enough control for what you are looking for. With a high end servo and a controller that works in 1uS steps, you might get up to 1,000 unique positions - but that may just be wishful thinking, and it would be expensive.

Rich H

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Simple Servo Tester, a kit from Gadget Gangster.

steambc

You guys are great. I'll be ordering the parts I need for experimentation.

Thanks to both of you for being available to us "newbies".

Brian