Using the Hall Effect in a Boss Rocker Wah.

[Frankgb]

Compadre's

A friend gave me a BOSS Rocker-Wah which I eagerly accepted, thinking I could build a decent Wah around it.

Unfortunately, it has a (I think), Hall Effect sensor as the pot mechanism.

Would anyone have a schematic for it or know how to use the Hall Effect?

cheers

Frank

[gez]

I don't know anything about the Boss but if it does have a Hall sensor then there'll be a magnet attached to the rocker (easy enough to test for).

If you're thinking of using the shell + the sensor and want to get some ideas, then there are a couple of projects which use a Hall Effect sensor in one of J Chatwin's books (Practical Electronic Musical Effects Units?).  There's also something over at Brett's site (click on his profile in the Members list and there should be a link).

gez

[Frankgb]

Thanks for that info!

[col]

Chatwin also uses them in the book "Advanced projects for the electric guitar"

[Paul Perry (Frostwave)]

Nearly all the "hall effect" devices one finds are magnetically operated switches. There aren't many linear analog devices like we want for this application. (I'm just saying that so experimenters don't waste too much time with stuff out of old keyboards or whatever).
The other thing is, the hall effect devices just generate a DC voltage depending on the magnetic field. So anything that you make from one, is going to have to be able to be operated by a control voltage.
The great advantage of the hall effect pedal: whereas an optical pedal gets around the problem of pots wearing out, the hall effect allows you to operate the unit completely submerged in a vat of sump oil. Forever.
Edited to say, put the magnet in the toe of your shoe. Then you don't need a pedal mechanism at all..... call it the Footloose if you want.

[brett]

Hi

There aren't many linear analog devices like we want for this application.

This is true for some applications where strong magnets are moved in close proximity to the sensor, but many of them have nice, linear responses to distance for average magnets and disctances of centimetres rather than mm.

Typically, these are "3 legged" devices.  One is fed the input voltage (usually 5V), one is grounded, and the other is the output.  Output is half the supply until a magnet comes near.  One pole of a magnet raises the output voltage and the other decreases it.

In my pot-less wah, I simply took the output of the hall effect device and ran it through a resistor and an LED.  The LED was next to a light-dependent resistor.  So when the magnet approaches the Hall effect device the voltage changes, the LED brightens (or dims, I can't remember), and the LDR resistance changes, just like cranking a pot.

Good luck with it.

[David]

Hi

There aren't many linear analog devices like we want for this application.

This is true for some applications where strong magnets are moved in close proximity to the sensor, but many of them have nice, linear responses to distance for average magnets and disctances of centimetres rather than mm.

Typically, these are "3 legged" devices.  One is fed the input voltage (usually 5V), one is grounded, and the other is the output.  Output is half the supply until a magnet comes near.  One pole of a magnet raises the output voltage and the other decreases it.

In my pot-less wah, I simply took the output of the hall effect device and ran it through a resistor and an LED.  The LED was next to a light-dependent resistor.  So when the magnet approaches the Hall effect device the voltage changes, the LED brightens (or dims, I can't remember), and the LDR resistance changes, just like cranking a pot.

Good luck with it.

Brett:

What was the "pedal travel" distance on your wah?

[brett]

Hi
the pedal angle was a bit more than a standard wah.  The magnet-to-HED distance was 2 to 3 centimetres (1") at the "top" and about one quarter of that at the "bottom".

[David]

Hi
the pedal angle was a bit more than a standard wah.  The magnet-to-HED distance was 2 to 3 centimetres (1") at the "top" and about one quarter of that at the "bottom".

So the total travel was .75 inch?  Did you use a real strong magnet?  Did you ever try anything to boost the total travel into the 1.5 - 2 inch range?

[Paul Perry (Frostwave)]

The field from a magnet decreases pretty rapidly as you move away, it's very difficult to make the field linear over any appreciable distance.
This isn't necessarily a bad thing though.
And any DC control voltage graph can be changed to another by diode function generators etc.

[David]

The field from a magnet decreases pretty rapidly as you move away, it's very difficult to make the field linear over any appreciable distance.
This isn't necessarily a bad thing though.
And any DC control voltage graph can be changed to another by diode function generators etc.

Yeah, isn't that the "inverse square" law, or something like that?  This is what I'm looking to do:  I want to feed the ADC input of a PIC16F88 with a variable voltage from +5V to as low as I can get.  I was going to use a slide pot to do this, but...  oh-oh...  mechanical part...  wears out.  I thought if I could feed the ADC with varying voltage from the Hall-effect sensor, there wouldn't be any "consumable" components.  What I need is to have total pedal travel of about 2 inches.

[Paul Perry (Frostwave)]

Well, the pedal travel - if you mean how far the tip of your foot moves - needn't have any relation to how far the magnet moves, because the magnet/hall unit can be closer to the axis.
By the way, the analog input to the PIC doesn't want to be higher than the supply to the PIC itself.

[David]

Well, the pedal travel - if you mean how far the tip of your foot moves - needn't have any relation to how far the magnet moves, because the magnet/hall unit can be closer to the axis.
By the way, the analog input to the PIC doesn't want to be higher than the supply to the PIC itself.

By Jove, Paul!  You're right!  I could put the stupid magnet anywhere on the pedal I want to.

EXCELLENT!     Got to get me a few of those Hall babies!   

Oh, yeah!  Regarding the power:  thanks for the reminder.  This toy, if I ever get it going, is going to run on 5V.