I am trying to implement a concept for somebody else.

Basically, I want to create a smart surface. I want to create a surface I can throw one or more tagged objects on that should all be recognized.

I am unsure how to this and what sensors I should use. I have been thinking about using one of the NFC ICs from NXP. However, designing a circuit board and buying this IC is too expensive for our idea. I'm also unsure of whether the surface area will cause problems, because it'll be quite large (think of a small coffee table).

I've also been thinking about other ways to recognize objects, but I have not come up with anything yet. I am probably not using the correct term.

Does anyone know of a type or sensor or technique to implement this?

Note: I am a computer engineer, not an electrical engineer. I know the basics, but really not much more than that, so I prefer a solution that is available as a simple IC or a complete circuit board with the really complicated things done for me by the experts :)

  • \$\begingroup\$ What about using a camera and image recognition? Similar to Microsfot surface table (not the tablet) \$\endgroup\$ – geometrikal Nov 15 '12 at 12:31

Look for RFID tags, and RFID sensors.

This RFID reader from SparkFun has a built-in antenna and a range of 200 mm and works with inexpensive 125 KHz RFID tags. Also, SparkFun has this USB RFID adapter to connect to a reader such as above, and provide USB data read off the tags directly to your computer or other device.

If you need to span a large area such as a coffee table, your options are: RFID reader with external antenna port, or a number of integrated antenna RFID readers arranged around the periphery of the surface

The mechanism used in some department stores, for instance, has their items tagged with RFID tags, and RFID antenna loops 3-5 feet tall and about a foot wide, on either side of the exit doors. The range is a few feet, which should serve the purpose. In your case, such an antenna would be a suitable loop of wire around the periphery of the surface.

Note that this mechanism will not allow your system to distinguish between tagged objects actually dropped on the surface as opposed to held above it. If the "dropped on" parameter is crucial, then multiple smaller-range RFID readers would serve you better - or a metal contact surface that works as your antenna, designed for a very small read range.

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    \$\begingroup\$ The ID-20 linked here is a very simple solution. I've used them in various prototypes for a few years now. It's really the best bet to getting a complete solution, especially in combination with the FTDI. A simple Python script can easily read the serial input and parse a library of tagged items. The only problem you might have is the size of the tags, if you want smaller tags you'll have to go to a higher frequency and make your own antenna. \$\endgroup\$ – Samuel Nov 15 '12 at 18:20
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    \$\begingroup\$ The ID-20 seems like a really nice solution, I don't need a lot of additional circuitry and the protocol seems simple enough to parse with a PIC. Thanks for the suggestion! \$\endgroup\$ – Pascal Muller Nov 15 '12 at 19:21

A better solution might be to use printed tags and image recognition. There are open source solutions for this - for instance, trackmate. All you will need is a printer, a camera, and a transparent (or possibly frosted) surface.

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  • \$\begingroup\$ I have been thinking about this, but the user then has to position the right side of the object to the camera. \$\endgroup\$ – Pascal Muller Nov 15 '12 at 19:18
  • \$\begingroup\$ @PascalMuller Well, yes. But that will be true for RFID, too - most RFID protocols have very limited range, especially through objects - and RFID doesn't provide you with any position information either. \$\endgroup\$ – Nick Johnson Nov 15 '12 at 19:28
  • \$\begingroup\$ I only need to track which objects are on the surface, I do not need to know their position on it. \$\endgroup\$ – Pascal Muller Nov 15 '12 at 19:33
  • \$\begingroup\$ @PascalMuller Fair enough. You'll still have range issues, though. Also in my own experience, although NFC supports scanning multiple tags at a protocol level, none of the readers I've tried actually support this - so you will have trouble if more than one tag is on the sensor. \$\endgroup\$ – Nick Johnson Nov 15 '12 at 20:55
  • \$\begingroup\$ If the scanner has trouble detecting multiple tags at one time, this would be problematic for me. The ID-20 seems to be able to do this from information I googled. \$\endgroup\$ – Pascal Muller Nov 15 '12 at 21:51

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