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'[OT] : back to page sensing again'
2005\10\25@183045 by alan smith

picon face
Well....the client was really hooked on hall effect sensing.  So I hooked up a demo circuit, and got some thin strip magnets (have to be thin) and found that based on where the circuit board is mounted, the magnets were too far away and didnt have enough flux density to them, unless I used a thicker magnet.  That of course, didn't play into the overall design, as the magnet would end up being too large

so....

As Mr Rolf pointed out...there are other choices....

The biggest issue with using ambient light to a PV type sensor is that it would be easy to be covered or not have enough light and give a false reading.

But, what about doing something with reflective IR?  in that....if there is a hole above an IR LED, nothing would reflect.  But I would need something that would emit and detect...are there such devices that are also inexpensive?

I like the idea of the coils, did a search for chess board piece sensing, came up empty as far as circuits.  

I'd like to look into this....any pointers to where some information and design data might be?

Robert Rolf <spam_OUTRobert.RolfTakeThisOuTspamualberta.ca> wrote:

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.



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.



               
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2005\10\26@052336 by Jake Anderson

flavicon
face
have you looked at rare earth magnets and creating a "magnetic circuit" to
boost field strength?

> {Original Message removed}

2005\10\26@080909 by Bill & Pookie

picon face
If a page was drawn across a circuit board containing photo sensors, could
they be used to determine page turning and direction?

If the sensors were aimed at some place on the book, would changing a page
be detected by them with one detecting something first so you could
determine which way page was turning?

And when thing about magnets, don't forget the magnetic ink used on checks.
The ink should be magnetized each time by dragging past a magnet.  To since
magnets there are also tape recorder heads and pickup heads from electric
guitars, but these may need the magnet to be moving fast past them.

Bill

{Original Message removed}

2005\10\26@134114 by Bob Axtell

face picon face
I had the task of picking a paper sensor a few years ago.

At first glance, it appeared that simply placing the paper in front of
an IR sensor
with the IR emitter behind it would work. But it did not because the
paper would
pass the IR. Worked sometimes, not ready for primetime.

The solution that DID work perfectly was a self-contained IR
emitter/receiver pair
in which the IR emitter sent the beam at a small angle, and the IR
receiver picked
up at a small angle. This set the "focal point" at about 2mm.

If the paper was NOT present, the beam was never reflected back. If the
paper was
present, the beam  reflected to the receiver. It worked very well.

The way we used it, there was a lot of tolerance needed, so I drove the
IR emitter
hard (50mA) but pulsed it very short and just once in 500mS.

Look up Fairchild QRD1114.

--Bob




Bill & Pookie wrote:

{Quote hidden}

>{Original Message removed}

2005\10\27@145728 by alan smith

picon face
THAT...is what I was looking for...the IR emmiter/detector pair.  I also ordered in some magnetic reed switches, not sure if they will work but worth a shot.

Can't do it with photodiodes as its to easy to defeat and needs some light source

Magnetics.....still looking into that, using a sense coil such as the reference to the chess game.

Thanks all....appreciate the suggestions.

Bob Axtell <.....engineerKILLspamspam@spam@cotse.net> wrote:
I had the task of picking a paper sensor a few years ago.

At first glance, it appeared that simply placing the paper in front of
an IR sensor
with the IR emitter behind it would work. But it did not because the
paper would
pass the IR. Worked sometimes, not ready for primetime.

The solution that DID work perfectly was a self-contained IR
emitter/receiver pair
in which the IR emitter sent the beam at a small angle, and the IR
receiver picked
up at a small angle. This set the "focal point" at about 2mm.

If the paper was NOT present, the beam was never reflected back. If the
paper was
present, the beam reflected to the receiver. It worked very well.

The way we used it, there was a lot of tolerance needed, so I drove the
IR emitter
hard (50mA) but pulsed it very short and just once in 500mS.

Look up Fairchild QRD1114.

--Bob




Bill & Pookie wrote:

{Quote hidden}

>{Original Message removed}

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