Smallest foot controlled volume pedal

[jfrabat]

Hi, guys!  It has been a while since my last post!

I want to make a passive volume pedal (yes, I knkw; electronics-wise, the simplest pedal EVER!) BUT...  I want it to be controlled by an actual pedal to use with my foot, but I also want the smallest possible footprint as my box barely has any space left.  Think Hammond 1590A size.  Not easy to adjust just right, but still possible to do with the foot live...

I was thinking of designing something to 3D print that is just big enough for a pot and 2 jacks, but then I thought maybe someone has already designed one, so I figured I ask here before firing up AutoCAD (I know there are simpler options for 3D design, but I already know how to use Autocad, so might as well use it!)).

I am also debating which option to use to turn the pot (gear, belt, string, belcrank), so if anyone has made somethimg like this and has any advice, please let me know.  As of now, I am leaning towards a 3D printer type belt and pulley.

[R.G.]

Don't do a rocker pedal. Use a largish round knob with coined/roughened edges and set the pot on its side so the edge of the knob sticks up a hair above the top of the pedal through a slot. Adjust by sliding your foot forward and back on the top of the pedal. No mechanism, only one 2"-ish knob to print.
A commercial phaser used this scheme long ago, early 70s or so. Can't remember the name right now.

[bluelagoon]

Here tis - or something similar

[RickL]

Not DIY, but I don't think I'll ever seen one that uses a treadle that is smaller. I've got one and it can be used without the pedal extensions.

https://reverb.com/ca/p/mooer-wahter-wah-pedal?hfid=37296909&utm_campaign=INTL-CA-Shop_unpaid&utm_medium=cpc&utm_source=google

[jfrabat]

Don't do a rocker pedal. Use a largish round knob with coined/roughened edges and set the pot on its side so the edge of the knob sticks up a hair above the top of the pedal through a slot. Adjust by sliding your foot forward and back on the top of the pedal. No mechanism, only one 2"-ish knob to print.
A commercial phaser used this scheme long ago, early 70s or so. Can't remember the name right now.

I like this idea!  I could 3D print an interior support for the pot to sit sideways close to the middle of a 1590A box(left to right) and as close to the top as possible, and turn a slim aluminum wheel on the lathe with knurling on the edge, and cut a slot on the top of the box for the wheel to protrude.  Maybe go to a 1590B and include a Bypass switch, but not sure I can squeeze a 1590B in the pedal box... 

Anyway, thanks for the ideas!

[MikeA]

From the steel guitar universe:  https://reverb.com/ca/item/4390294-moyo-mini-volume-pedal

[bluelagoon]

The center wheel might be easier to control with a silicone or rubber outer tyre on it. Certainly would be grippier to your foot.

[Shoeman]

The older Boomerangs used the design that RG suggested.  The control is a bit bigger but it works very well.  And it is rubberized to minimize slippage too. 

[ElectricDruid]

The older Boomerangs used the design that RG suggested.  The control is a bit bigger but it works very well.  And it is rubberized to minimize slippage too. 

Like a synth "Mod Wheel" for the feet!

[FiveseveN]

Or more recently, Classic Audio's Expression Roller or Chase Bliss EXP. Here's a teardown of the latter: https://blog.synthesizerwriter.com/2021/11/the-chase-bliss-exp-pedal.html

[Phend]

^ Very cool and it is an...
  "astonishing piece of mechanical engineering"

[R.G.]

The Classic Audio and Chase Bliss seem to have this covered for a commercial product. I'm guessing that they share similar mechanicals inside. The tear-down on the CB shows some build-it-like-a-tank engineering to address some of the issues below.

If you're 3-d printing a foot activated knob, you might also need to think about some of the human factors involved.

There's going to be a human stepping on the edge of the knob, and they're going to be involved in a lot of other activities at the same time. The knob needs to be useful for the human and relatively immune to the weight and over-travel movements of the human.  The commercial products seem to solve this with a heavily supported mechanical wheel, heavy bearings and frame, and a belt drive.

I have limited foot dexterity (translates to "I'm clumsy with my feet, especially when playing guitar" 8-) ) so it seems natural to me to worry about whether I could use a roller-knob. A common pot travel is 270 to 300 degrees. This maps to a linear travel of the human foot by the diameter of the knob, so foot travel end to end of the knob will be the knob diameter times pi. A 2"-ish diameter knob would have an end-to-end foot travel of the diameter times the fraction of a full turn; this works out to 2" * 3.14 * 270/360 = 4.71".

For a 2" knob, your foot would have to move the edge of the knob about 4.7". How easy that is depends on what shoes you're wearing. Flat soled shoes make it easy to go way longer than that, cowboy boots may have trouble covering the whole range because of the high instep arch. A 1" diameter knob would have half the end-to-end travel, about 2.36", so smaller foot movements would suffice. At some smaller diameter, fine adjustments would be tricky.  The knob diameter probably needs to be larger than the pot diameter, to keep the mechanics simple.

I would inevitably try to push the knob further to maximum or minimum than it can rotate, so I would need some kind of reliable mechanical stop on the knob to keep from overtraveling the pot, or a slip clutch in the pot itself. A 3d printed knob might include an inner knob to move the pot, and an outer ring that has friction on the inner knob but slips when the pot can't turn any more. The commercial ones seem to have hard mechanical stops. I wondered if the internals of the CB could have a smooth belt with a tension adjust to allow overtravel to be non-fatal. 

I would also probably put a lot of weight on the thing, possibly damaging a hard-mounted pot. A semi-flexible pot mount or a semi-flexible shaft connecting the pot and the knob would let it survive this pretty well. Again, 3-d printing a knob with a shaft extension or a semi-flex shaft would be useful. A stiff spiral spring between pot shaft and knob center would also work. The commercial pedals solve this with very tough bearings and wheel and an isolation belt drive.

[ElectricDruid]

I wonder if there's a more hi-tech solution to this?

I mean, the problems with the pot are mostly mechanical, limited travel, weak plastic shaft, etc etc. These same problems have turned up in other volume pedals and been solved various ways, including using lamps and LDRs with a shutter between them moved by the pedal. Would something like that be possible? The wheel could be clear acrylic with more or less black covering on it, so an LED shone through it gives more or less light to an LDR on the other side.
Or perhaps something like a old mouse wheel could work, with a slotted disc or some other rotary encoder, and then a value that is created that can be used to control a VCA for volume control. Obviously this is more complicated than just a pot, but it also avoids a lot of the problems of a pot, and offers a lot of possibilities beyond simply being a volume control you waggle with your foot - programmable? MIDI controlled? etc etc

[Phend]

"This force-sensing resistor (FSR) from Interlink Electronics is a passive component that exhibits a decrease in resistance when there is an increase in the force applied to the 1.5″ × 1.5″ (4 cm × 4 cm) active area, allowing you to create a sensor that is able to detect force or pressure. With a force sensitivity range of a few grams to a few kilograms, this sensor is optimized for use in human touch control applications."



or

"Manufactured by Spectra Symbol, these are nice little ribbon controllers (also known as 'soft potentiometers') with an adhesive backing. This shape is a circular soft potentiometer with a donut-shaped sensing region whose outer diameter is 55.96mm/2.2in and inner diameter is 35.63mm/1.4in.

There is a nominal 10K resistance across the two outer leads. The middle pin resistance with respect to either of the outer pins changes depending on where on the strip one presses. When no pressure is applied, the middle pin floats, so be sure to use some sort of weak pullup, such as 100K ohm.

To use Connect one side pin to ground via a 10K resistor in series. Connect the other side pin to your Vcc power line (3V, 5V etc) via a different 10K resistor in series. Then read the analog voltage on the center pin. It will range from 1/3 Vcc to 2/3 Vcc . Do not connect to Ground and Power directly!"

[ElectricDruid]

Oooh, I like this idea! Yeah! No moving parts - you just stand on it!

[R.G.]

I wonder if there's a more hi-tech solution to this?

I mean, the problems with the pot are mostly mechanical, limited travel, weak plastic shaft, etc etc. [...]. Obviously this is more complicated than just a pot, but it also avoids a lot of the problems of a pot, and offers a lot of possibilities beyond simply being a volume control you waggle with your foot - programmable? MIDI controlled? etc etc

Yep. The one I was most attracted to was the variable capacitance action in the FX-17 wah pedal. A grounded metal shutter was kept off the traces of a PCB by a teflon or mylar sheet. Rocking the footrest moved the shutter and thereby varied the capacitance of the PCB section to ground. This varied a frequency/duty cycle/something, which was sensed and created a control voltage to an OTA filter. Obviously, the control voltage could be used for anything else voltage controlled. It wasn't clicks on an encoder (although I've seen and done that in other contexts) but for a low accuracy analog sweep, it worked very well. Slick application and circuit, all analog, which lots of people like. Easy enough to digitize the derived voltage as well.
I speculate that a PIC could digitize a variable capacitor directly by measuring timing on a constant-current fed variable capacitance and then spitting out a computed control voltage. I have used a capacitance digitizer for measuring water level in a tank with the grounded water covering a variable amount of the insulation over a loop of water in the tank. Works.

"This force-sensing resistor (FSR) from Interlink Electronics is a passive component that exhibits a decrease in resistance when there is an increase in the force applied to the 1.5″ × 1.5″ (4 cm × 4 cm) active area, allowing you to create a sensor that is able to detect force or pressure.

Clever. Only bad thing is that it has no "stay where I left it" and will always return to lowest/highest/etc. state when you take your hand or foot off. That's great if you want return-to-zero, not so much if you don't.

[Phend]

Google home volume control. Works well. Also works with voice, provided it is setup.