Detecting wah angle with a Hall effect device

[brett]

Hi
Looking through the Mouser catalog for a linear Hall effect sensor, I came across an encapsulated device that senses angle (page http://www.mouser.com/catalog/631/1616.pdf bottom of page, part 540-AN101101).
Unfortunately the cost is a bit too too high for a DIY wah or volume pedal.  But another manufacturer might have something similar for less $$$ ?
cheers   

[R.G.]

If' you're willing to go to that much trouble, capacitive sensors are easy. Make your pedal motion slide a metal plate over another insulated plate, sense the capacitance change. Or use a conductive fluid on the inside of an insulating chamber with one half of the outside coated with foil.

Use your favorite method for converting capacitance to voltage. 7555, PIC, RF oscillator, charge balancing, etc.

[soulsonic]

RG,
I disassembled an old organ recently and I was surprised to find that the volume pedal was controlling a large variable capacitor - one of those big open air ones like you see in a HAM radio. Is this a similar concept to what you described?

[brett]

Of course, you're right RG.
Note to self: be more practical ya mad scientist. 

Someone was asking about those radio-style gang caps here a while back, and the price was fairly good for quality, high-value gangs (about $5 for a quality 500pF job, if IRC).
cheers

[R.G.]

I disassembled an old organ recently and I was surprised to find that the volume pedal was controlling a large variable capacitor - one of those big open air ones like you see in a HAM radio. Is this a similar concept to what you described?

Yep, same idea.

But that's still a rotary shaft you have to couple to. What is really neat is if  you can cobble up a variable capacitor that doesn't need rotary conversion with a rack and pinion.

[GFR]

There's a dod wha pedal like that:

http://www.diyguitarist.com/DIYStompboxes/FX-17.htm

[David]

Let's not let this idea die an ignominious, anonymous death...
Especially since I've spent a lot of time thinking about it, and never coming up with an answer I liked.

Ladies and gentlemen, think about it in this context:  If you buy a Cry Baby-type wah pot, it could easily cost you at least $25 USD.  With shipping, you could be at more than the cost of the part Brett has identified.  Ah, but when you consider that our much-loved pot has a limited lifespan and you look at the number of operations this thing is rated at, somehow the cost difference doesn't seem to be quite the showstopper it started out as.  Comments, anyone?

Here's something else:  Note where R.G. indicated how to do capacitive sensing.  Consider this:  there is a build article out on the Web for the PAIA Oz.  These days, the thing is more or less made from unobtanium since the top-octave generator chip has gotten so scarce and so pricey.  However, one gem that article DOES contain is a PCB diagram for a...  capacitive touch controller.  Now, I grant you that it probably is based on skin resistance or capacitance or something along those lines, but perhaps some creative adaptation will result in something that puts this into our ballpark.

Oh, and along the lines of non-pot, one should also consider flex sensors...     I know I have been...

[earthtonesaudio]

If you have a wah shell, there's always the Morley approach with the LED/LDR and the variable aperture to control light reaching the LDR.
It's nice because you have a fixed light output and you can make the aperture have any taper you want, but it would be a chore to have to re-shape the aperture every time you wanted to change the taper.

But if you were really meticulous, imagine the possibility of having different taper presets... Just select a different shaped aperture, and you go from "wah" to "haw" to "wahawahaw." etc.

But the fun might wear off pretty quick having to open it up and change out a physical part.  So how about this (for the true mad scientists):
The movable part that blocks the light is a high resolution transparent LCD, and you can set the taper electronically.  Have tons of presets, even tapers that change while you play, according to dynamics or how fast you move the pedal...

[David]

If you have a wah shell, there's always the Morley approach with the LED/LDR and the variable aperture to control light reaching the LDR.
It's nice because you have a fixed light output and you can make the aperture have any taper you want, but it would be a chore to have to re-shape the aperture every time you wanted to change the taper.

Have you actually attempted this?  I have.  It is not trivial.

[earthtonesaudio]

Nope, moving parts scare me.

I can imagine the level of difficulty though.


How about this: the pedal actuates a bellows which forces ferrofluid into a balloon inside the pedal, and the balloon is constrained by a small tube with a bunch of turns of wire wrapped around it, making a variable inductor...

[Sir H C]

I thought that a company Melexis has a hall effect device that is multi-axis, for joy sticks, so it should be pretty cheap. Seems they have the module for $5 at mouser.

[Nasse]

I think there is lots of info whats available today, in this month Elektor Electronics. I have not looked it but believe so