interesting expression pedal

[Gus]

Saw this you tube
could be a cool for a synthesiser or?

https://www.youtube.com/watch?v=ag_p8gayrTs

[iainpunk]

rainger fx - igor
probably easier to use for voltage control than variable resistance. just use a piezo pad and use an opamp to multiply the DC voltage that gets created.

cheers, Iain

[Mark Hammer]

I exchanged a few e-mails with David Ranger, and IIRC, he uses a force-sensing resistor for Igor.

[RickL]

The thing that caught my attention was the mention of pots with small rotation ranges. One of the issues with the standard wah/volume pedal is that it won't rotate the pot through its full rotation. Not normally an issue with a wah, but if you want to use it to pan or to sweep from the maximum to the minimum of the pot's range, like with the Anderton wah/antiwah, they don't work so well.

Put a pot in a wah shell that only requires 45 degrees of rotation to cover the full range and the issue goes away. The only thing you might have to deal with is stops to prevent over rotation.

I wonder if Roland/Boss would sell these pots separately or if they're available from another source.

[Mark Hammer]

The feasibility or advisability of making any pot move its full rotation in response to some externally-applied force will depend on just what exactly that force IS. In the case of a wah pot or volume pedal, the full force of a human body of unspecified mass and acceleration is being concentrated on a small device, via the mechanical advantage of the rotation mechanism.  As a safety precaution, to avoid breakage, the mechanism results in 10-20 degrees less movement/rotation at each end of the wiper's travel.

HOWEVER, if the application of the mechanism is understood/presumed to be in the context of much less torque than a 220lb guitarist in steel-toed workboots doing a frenzied speed-metal version of Voodoo Child, one can afford to go the full 270 degrees.

I have one of those little Yamaha CS-01 synths, which has an input jack for breath controller.  One of these days I have to explore that.  The best example I can quickly think of, of the feel a breath-controller affords, is the old Lionel Richie tune "You Are" ( https://www.youtube.com/watch?v=DXMDWfLclNY ), where you can here some of the synth notes ease in, the way a singer would gradually emphasize a held note.

[ElectricDruid]

As it happens I've been working on an expression pedal over the last few days, very intermittently.

I have an old volume pedal I pulled out of a dead organ. It has a pedal that moves a blade between a lamp and an LDR. How to get the 0-5V range that I'd like to see out of it? The obvious answer: add a microprocessor and do some calibration. So I've stuck a little 8-pin PIC in it, and replaced the 12V bulb with a white LED so I can run it all from 5V. That means it should be possible to power it up from an "expression pedal" input, since they usually provide 0V and 5V connections. Dunno if the PIC will run from 3.3V. Maybe, haven't checked. Some do. So maybe it'll work on 0-3.3V expression pedal inputs too.

The software has the LDR and a resistor connected as a voltage divider sent to an ADC input. I also have a "calibrate" button connected. The first press puts it in calibrate mode. Put the pedal at the far end of the travel, and then the second press sets the "max" position. Finally, put the pedal in the "minimum position and press a third time. The chip works out the offset and scaling required, and stores the settings in EEPROM so you don't have to do it every time. Then when you rock the pedal from one end to the other, you get a full 0V to 5V range (from a PDM output in this case).

I'm hoping once I've got it to where I'm happy with it that I can tweak it so you can set "max" and "min" either way around (so you can have the pedal working "backwards" if required) just by setting up the calibration that way. Currently the math won't cope.

Since the actual mechanics of the system are largely irrelevant, you could do this with pretty much any type of variable sensor that can provide a voltage input to the chip. Either an FSR or a wah pot or whatever. The process would be identical: set cal mode, set max, set min, done. 0-5V output.

[iainpunk]

I exchanged a few e-mails with David Ranger, and IIRC, he uses a force-sensing resistor for Igor.

that's interesting, i thought i read somewhere that its a piezo disc, but that could just be my bad memory.

cheers, Iain

[Mark Hammer]

Could be mine, too.  I'll have to check my e-mail from 2 years ago.

[anotherjim]

I've been looking into my Roland EV-5 Expression pedal which isn't all that old but developed scratchy operation. I could get it going by squirting some contact cleaner into the pot, but after a while, it starts doing it again.
The treadle pot is "different".
The pot is a standard looking Alpha 16mm but driven by a crank in an escapement plate from the treadle. The crank secures to the pot shaft with a single setscrew and it's very easy to set the action. They use the pots anti-turn lug to fix its position in case bracket.
However, all is not quite straightforward. That pot is funky, and not necessarily in a good way.
To begin with, there's no sealing cap of the pot can to keep crap out and there were great gobs of grease on the actuator metalwork. The grease getting in might be what started the trouble.
The pot travel is very short, maybe only about 30deg. It's marked E3 10k and yet despite the short travel, it can still measure a 10k sweep.
I took the pot out and took the can off to look inside. As you might have guessed by now, the pot only has a short arc of carbon resistance, Either side of that, the wiper runs onto a conductive layer. I've never seen a pot track like it before!

[ElectricDruid]

If you're Roland, you can order any kind of pot track you like. It can be as weird as you like, but as soon as you say "100,000 units" everyone's ears prick up and they start telling you how they can deliver the first batch in fortnight!

Unfortunately the rest of us aren't in such an exalted position

[iainpunk]

If you're Roland, you can order any kind of pot track you like. It can be as weird as you like, but as soon as you say "100,000 units" everyone's ears prick up and they start telling you how they can deliver the first batch in fortnight!

Unfortunately the rest of us aren't in such an exalted position

i'd love to find a manufacturer who does unique pot ideas *, mine is ''turn through'' pots.
those are pots with a ring of resistive material (would have to be extra wear resistant) with pads on opposite sides of the ring, and a wiper that can turn around and around and around, since the whole thing is a continuous track.

cheers, Iain

*Pot idea: an idea for a potentiometer conceived through the smoking of pot/devils lettuce/cabinas