Pedal Setting Reader - Is this possible?

[brasco1234]

Hello-
First, let me say that I don't know anything about electronics really but it seems that the people in this form definitely do. Thus, i thought I would post this here.
I am interested in a way to make setting my pedal effects more precise. I have all 8 of them getting their power from a common supply (A Voodoo Labs Pedal Power 2). I don't know if that helps what I'm asking, but it seemed like it might. I want a way to save presets for each pedal-not in the sense so I won't have to turn knobs or anything, but rather, something that would register all 8 pedals' knobs locations. Then, when you turned a knob on a pedal, a light would indicate when you had the knob on the correct saved setting. This would allow me to replicate the exact same knob positions everytime. Even having this on only one pedal would be fantastic if I couldn't do it on all 8 through the common power supply.
Has anyone seen anything like this? Is it possible? Is it ridiculous?
Thanks everyone for your help in advance!
Chris

[vdm]

i think you would need some kind of digital chip to do it all... you want something akin to a multi-fx pedal yes?

my suggestion would be to get a pen and draw a line on the pedal 

sorry.. but i think it would take quite a lot of work to make it all happen

[petemoore]

  Get a 'dual face' like on a clock, and outside template shows the one setting cause it's blue, the inside ring shows the other setting in red.
  Tricky, but could be done, I've seen old military/navigational stuff that had 1+ settings indicators like this...high tech versions that'd be hard to 'just do'.

[Processaurus]

  Get a 'dual face' like on a clock, and outside template shows the one setting cause it's blue, the inside ring shows the other setting in red.
  Tricky, but could be done, I've seen old military/navigational stuff that had 1+ settings indicators like this...high tech versions that'd be hard to 'just do'.

My funky radio shack PA has something like this on the master volume, its a transparent ring with a bright red dot on it, and its underneath the big volume knob.  It has a nice smooth feel when you turn it, like a pot.  Its really nice with the PA, when you want to know how loud you can get it before feeding back, but want to turn it down when stuffs getting moved around, plugged in, etc.  Not exactly a common potentiometer accessory, though.

Lo Tech:  I've seen premade adhesive arrowhead pointers for marking settings.

[brasco1234]

The problem is my settings change for every song. I do write them down now, but with something as tempremental as a delay time knob it can be hard to get the exact setting.
It seems that my idea is far too complicated, so how about something easier I thought of. Once again, I could be showing my ignorance, but if I hooked a voltage meter up on the pot that controls delay time, would the meter change as the knob turned? In other words, I could monitor the exact voltage of the knob and write that down, then just turn the knob till it matched each time. Is this possible? I saw some small LED voltage meters on Ebay that I could permanently hook up onto the pedal. I don't need to the LED to show anything fancy, just a number that corresponds to the knob position. Whatever that number is doesn't matter, as long as it changes when the knob does.
Thanks for all your help so far!
Chris

[Mark Hammer]

There ARE digitally addressable pots made by Dallas Semiconductor, among others, that permit precise replication of a pot setting.  The problem is that you have to have something that retains the digital code for that setting in memory and is capable of dumping that value to the pot.  Obviously not exactly ripe for a quickie mod on a pedal, is it?

Another route is to use something like a multiturn pot that allows for much more precise adjustment.  A conventional pot takes all possible resistance values and squishes them into something like 270 degrees (if that) of rotation.  Factor in pot taper, and the difference between a delay of 200msec and 300msec could be a millimeter of pot rotation and tricky to nail again every single time.  Replacing a regular pot with one that requires 10 complete rotations to cover the entire range of values will spread such a difference across a much broader range of rotation, where the diffrence between 4 and a quarter vs 4 and 3/4 turns clockwise may be negligible, and extremely tolerant of a wee bit of error on your part.

Finally, another route is to mimic multi-turn pots (which are pricey, not always available in the value you need, and may not fit your chassis either) with "range-setting" toggles.  So, say you have a delay-time pot of 100k.  Replace this pot with a 50k pot and a toggle that adds or shunts a 47k (or 51k) fixed resistor in series with this pot.  What you effectively do in this instance is to redistribute all possible resistance values between  zero and 100k across twice as many degrees of rotation - not quite a 10-turn or digital pot, but certainly more precise and replicable than a single 100k pot.  Something like this can be particularly useful when the taper of a pot is especially critical to precisely nailing certain values, like delay times or LFO speeds..

[spudulike]

I had a thought about this a while ago.

I had an OD that had a real sweet spot but took an age to dial in exactly how I wanted it, and thought along the same lines. How about using a Wheatstone bridge like this



The monitored pot was my OD control, at 100k log. Lets say I replace it with a dual gang, same value. Top section is OD control, bottom is monitor.

I set it at the sweet spot, and then balance the bridge using the trimpot. When balanced, there is zero current in the LEDs so they are extinguished. If I move the OD pot, one or other LED lights, I move the pot until the LEDs are out and Im back to my sweet spot.

Just a thought and probably way wrong ...

[PharaohAmps]

Good idea with the Wheatstone bridge.  I'm not an expert on them by any means but it's a good start.

The one problem I can see is that your "Pot Monitored" pot (we'll call it Pm) is in the bridge.  Any kind of current run through it or voltage run across it is going to upset the bridge.  Not to mention that it's set up as a rheostat, or a 2-terminal variable resistor.

The way to work it in real life is to use a dual-gang pot for Pm.  One section interfaces with the bridge and the other is in the effect.

However, even this approach is somewhat problematic.  What use is a preset pot position, really?  You'd be better off replacing your knobs with ones that lock your pots in one spot, these are available.  If all you want is the pedal to be set in one spot and never move, then dial your pedal in and replace the pot with fixed resistors.

A much more useful approach IMHO is to do the old "Adding Presets to Vintage Effects" trick outlined by Craig Anderton in his second DIY FX book.  I think you should buy the book so I won't give it away here, but it basically entails adding some small trim pots to your pedal and using a switch to select the one you want.  A 10 or 20-turn trimpot won't move much even if whacked seriously in transit, so your settings would stay put.  You could then use your panel mounted pot to dial in settings to compensate for the room / situation / song.

Just a thought.

Matt Farrow

[H S]

I set it at the sweet spot, and then balance the bridge using the trimpot. When balanced, there is zero current in the LEDs so they are extinguished. If I move the OD pot, one or other LED lights, I move the pot until the LEDs are out and Im back to my sweet spot.

There's a broad range of voltages across the bridge where neither LED is lit--between about -1v and +1v.

[brasco1234]

I do not want the pedals to be set at one value. I need to change them to precise settings. Adding different pots is too much, since my settings change for each song. Can anyone comment on my earlier idea of putting a voltage LED meter on the pot to see what it is set at?
Thanks,
Chris

[bioroids]

The problem with the voltage meter is, in some circuit configurations (if not most) the turning of the pot doesnt change the voltage at the wiper.

When I started using pedals I wrote all the settings on a notebook and had to change everything between songs, while the rest of the band (and public) waited looking at me... I'm pretty particular on the sounds I try to get, but I the end, I got rid of the notebook and just concentrated on playing, turning the knobs as needed by the feel of the moment... it's much more fun playing that way. Anyway that's my point of view. 

Good luck 

Miguel

[Hal]

I actually JUST did a thing with a PIC that read a pot with an ADC, dispayed a number between 0 and 9 based on the pot's location.

Not really practical for a pedal.  I ditto the drawing lines :-D.  Either taht or replace your pots with screwdriver adjust pots so they don't get screwed up (excuse the pun) when you don't want them to.  Anything else seems kinda impractical, especially when it is times eight.

[Joe Kramer]

Craig Anderton did an article once on adding presets to analog pedals, something along the lines of this: Use a rotary switch to select among several trimpots which are adjusted to your favorite settings.  You could also include the original variable pot as one of your switch selections.  The only problems with this method are finding the room for the trimpots and switches, and a possibly expensive rotary switch.  If you can overcome those obstacles, the method would certainly work as a way to add presets.

Joe

EDIT: Sorry for the redundancy Matt--didn't read your post all the way through. 

[PharaohAmps]

OK, here's how you do it.  It's not easy, and it's not simple, but it IS possible and it would work.

First up, you need a uC (microcontroller) of some sort.  A PIC would do, or one of the Atmels or similar.  You need as many ADC inputs as you have knobs whose settings you want to read.

Second, you need to replace all the pots in your pedals with dual-ganged pots, or at the very least install a switch that would disconnect the pot's terminals from the effect circuit and connect them to a measuring input on the uC.  With the dual-gang pots you could adjust the settings more easily, but with the switches you could get by with a lot less inputs on the uC.

Third, you need to program the uC to read and remember the settings of the pots once they are set to your satisfaction.  This part is pretty easy once you understand programming PICs or similar.  You'd really only need one LED to tell you that your pot was correct, since you could program it to only monitor a pot that was in motion.  You could even program the thing to flash once you got close, and then change the flash rate as you "zero in" on the correct setting.  Or a second LED or bi-color LED could be used to note the exact position.  These details are best left to the user / designer.

So you're looking at quite a lot of work here, and for someone who admittedly doesn't "know anything about electronics really," you might be in a bit over your head to start.  The spirit of this board is to help everyone as much as we can, and I always try to do that.  We are also not the kind of people to just jump on newbies and shut them down without trying to help.  That said, I think your idea is a swell one but it might be a little bit impractical as it stands now.

I do not want the pedals to be set at one value. I need to change them to precise settings. Adding different pots is too much, since my settings change for each song. Can anyone comment on my earlier idea of putting a voltage LED meter on the pot to see what it is set at?

In order for this approach to work, you'd need to disconnect the pot from the circuit and measure its resistance, not the voltage across it.  Others than I are better suited to give you a basic grounding in electronic principles, and I'd take them up on it if it's offered.  Your ideal, swell as it may be, is kind of impractical for changing settings quickly at a gig, and requires far more effort than cramming a couple of Chiclet-sized trimpots into your pedals.

I'm going to go waaaay out on a limb here and suggest that you're basically asking for a way to do multi-fx things with 8 pedals?  Is that about it?  Patch recall with different settings on each effect?  You want to be able to bend over and twiddle your knobs between songs, and to make sure that you get the right sounds?  There is PROBABLY a way to do it.  Probably even a way without resorting to digital hoodoo.  Good luck to you!

Matt Farrow

[johngreene]

However, even this approach is somewhat problematic.  What use is a preset pot position, really?  You'd be better off replacing your knobs with ones that lock your pots in one spot, these are available.  If all you want is the pedal to be set in one spot and never move, then dial your pedal in and replace the pot with fixed resistors.

I know this isn't exactly the topic, but the easiest way to achieve what you mention above that I've seen someone do is to take the knob off, slip an 'O' ring over the shaft of the pot and then replace the knob. The knob mashes down on the O-ring and provides friction. It takes a lot to turn the pot but it does't move with the normal banging around in a gig bag.

--john

[Mike Burgundy]

How about, if you are going with microcontrollers, sampling several pots (can be done sequentially) for their settings (maybe this is over-simplifying, but what if you put a pot between ground and well-regulated 5V and digitally sample the wiper?).
This can then control a series of digital pots.
If you want *precise* control, include an alphanumerical display and blammo. More than 128 steps you'll never need, but I'm guessing you'd probably have enough range with 100 settings - that's a two-number display. Want more? Include the dot - 200 settings right there. I've seen a mixing desk that can be adjusted to 1/20th of a decibel, but for the life of me I can't think of a reason why one would need this in a non-scientific environment.
Aside from the PIC, you'd also need some peripherals, (MOS) switches for the sequential thingy, encoders/decoders to be able to use BCD or whatever code you wish to shove numbers around, etc.
It's not that hard, but it does run into a substantial parts-count.

[octafish]

I am reminded of Neil Young's "whizzer". Get your minds out of the gutter. This was/is a mechanical device that allowed preset amp settings to be acheived with the flick of a switch. The whizzer was attached to the knobs of an amp and used motors to turn them to their presets. Me, I use masking tape on the settings (Both amp and boxes) with different  coloured marks for different sounds.

[niftydog]

By the time you've implemented any of these approaches, the old "time is money" adage means you could have saved your time and used the money to buy multiples of the pedals!

I'm a fan of glow in the dark stickers myself, but on some pedals I manage to simply remember the appropriate settings.

[brasco1234]

Okay, first let me say thanks to everyone who has helped. I see there could be a lot of work involved. PharoahAmp, you replied to my latest post about using a voltage meter. I would have to unhook the pot from the circuit to check its resistance? I can't just connect a voltage meter in there somewhere?
I actually got a reader from Radio Shack today and played around with it. By connecting it to various parts of the pedal's pots, I found that it did vary depending on where the pot was set. This seems like what I wanted it to do, but now, how do I apply it?
I have pretty much given up on my original idea of saving the settings. Now, I just want one pedal to show me the resistance readout on one pot (for delay time).
Who can help me out?
Thanks again for all your help so far,
Chris

[niftydog]

I can't just connect a voltage meter in there somewhere?

To get accurate readings the device being measured must be electrically isolated from the circuit else it might be adversely affected by other components in parallel. So, yes, you have to disconnect the pot to read it accurately. However, whether you need to read it or not is debatable. Quite simply, if you're just after a repeatable setting you can ignore accuracy.

Hook up a voltmeter to the delay time pots wiper and see what it does when you adjust it. If the voltage varies, then you're in business. Take note of the read out at the required delay times and you're done! Now it's just a matter of installing the wires and mounting it somehow.

Can't help but think you need to consider a tap tempo delay pedal though! Just a thought...