How does IPOD's Touchwheel work ???

[iso9001]

I wanted to integrate a similar style of touch pad in my project. Already using a microcontroller with some free pins, not round rather I'de prefer vertical like the Creative Zen Touch.

I found the company that makes them but I think it should be rather easy to reproduce, just not sure whats going on behind the tocuhpad.

Look here,
**broken link removed**

I'm not sure what kind of circuit they have connecting each lighining bolt pad. They're site says its capacitive, but does it NEED to be ?? Or how much work would really be put into a capactive cirucit anyway ?

I only have say 8 or 9 buttons layed out vertically, that should only be a single adc read then a data lookup no ?

 

[DirtyLude]

I've never actually touched an iPod, but I assume it's a capacitive touch switch. I use the q-prox chips for that. They are pretty cheap from digikey for individual touch buttons. I know they have a slider chip as well, and it looks like they just added a scroll wheel application, the same as the iPod.

https://www.qprox.com/products/touch.php

 

[iso9001]

Thats perfect!

I'm already using SPI to thats really a no brainer!

I really like the slider w/ timeout thing. Pretty cheap too. But how well do they work ??

Any comments on use with a light glove, debouncing control, etc. Looks like PCB layout is a pretty big factor, also are they showing some surface mount peices on each pad, are those leds, resistors or caps, I wonder ?

How about extra components to make it work? Anything I need to consider?

 

[DirtyLude]

I've only used the single pad chips. You can see from their reference designs not much else is needed. You will need some odd capacitors that I had to order special, 1nf, 22nf, and such; check the datasheets. I haven't used the slider, but the things between the pads on the reference design are just simple resistors. Resistance should increase at a specific rate along the slider.

I would like to use the slider thing, but I just don't have a project where it would be useful. I have too many 'oh wow' things I've played with that I can't find any real use for.

The documentation for these chips is complete and very well done. You should be able to get everything you need from there.

 

[iso9001]

Just reading over the docs,

Looks like it'll report absolute position over SPI, thats fine, I can determine a slide off of a few reads.

I need to read over the datasheet still. I can't tell if those resistors are touch side or on the back of the panel. I would have figured that you'd want the acrylic or glass to be as close to the pcb as possible, putting the resitors right there doesn't make a ton of sense, unless for their examples they just don't care if they get 100% maximum possible distance.

Now that I think about it resting the glass on the restistors is a pretty good way of making sure its where its the designed distance from the board.