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: >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 ----- >From: "alan smith" >To: "Microcontroller discussion list - Public." >Sent: Tuesday, October 25, 2005 3:30 PM >Subject: [OT] : back to page sensing again > > > > >>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 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. >> >> >> >> >>--------------------------------- >> Yahoo! FareChase - Search multiple travel sites in one click. >>-- >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist >> >> > > > -- Note: To protect our network, attachments must be sent to attach@engineer.cotse.net . 1-520-777-7606 USA/Canada http://beam.to/azengineer -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist