From what I've been able to gather of the requirements so far,
you have 10 or so plasticized pages, in a binder, that flip
down/up much like a clip board would. You also need very low cost,
($3 in quantity) and presumably have a PIC/LCD so you have some
sort of power for the sensors.

Your sensor choices seem to be magnetic, optical, mechanical.

If the number of pages is small, then 11 optical sensors
along one of edges to detect page tabs seems to be a clean
solution. Use LED carrier modulation and the 11th sensor
to remove ambient light concerns. I don't think you can do this for $3
but I'm not into mass manufacturing so it may be doable.

Or as one poster suggested, use the shadow effect
since you need light to read the document, so you don't need
to emit anything. Downside is dirt on the sensors and
a page half in light, half not.

For dirt resistant detection, hall effect with thin magnets
(like fridge magnets used for sales promotions) can be sensed
out to 1/4". You would need top/bottom magnetization rather than
the more common alternating stripes. You can get high density this way.

You could also look at coils that are HF excited, and have metallic
disks on the pages that would change the coil Q or L. This would
make the lumps in the pages much less noticeable. You could binary
code the sensors because the more iron you throw above a coil,
the more the L/Q shifts. And using different metals would give
you different detuning as well. An analog mux and oscillator are
all you'd need to read your coil array. Look for 'chess board'
'piece' 'sensing' for existing ccts to do this.


Do let us know what you find out works.

Robert


Sean A. Walberg wrote:

> On Tue, 2005-10-11 at 12:16, Spehro Pefhany wrote:
> 
> 
>>Have a look at the Leappad product in your nearest high-end toy store. ;-)
> 
> 
> Alas, the last one I looked at required you to touch the wand to the dot
> at the top of the page before starting, each page's dot was offset a
> little so the sensors at the top could figure it out.
> 
> A former coworker had a digital pen that worked well, it came with a
> special book that had a fine pattern encoded on it.  The pen would write
> on the page in ink but also sense where it was and what page it was on
> based on the pattern.  Later, you'd upload what you wrote to the
> computer.  Unfortunately it doesn't meet the OP's requirements, I think
> the pen was a couple of hundred dollars and each notebook was $10-$15.
> 
> Sean
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