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I am prototyping an RFID system that can detect a specific object about 50cm away. I've tinkered with the idea of proximity sensors but the issue there is the inability to strictly trigger when a specific object is detected. I started reading about RFID tags and figured that could be my solution. I've seen DIYs of tags in animal collars so that pet doors are opened when the collar is detected, and my system is something similar. The main difference would be the range. The object would essentially have the tag. I need my reader to be about 50cm away, and technically the signal can't be linear since the object can be in different locations within that 50cm radius. Also, the tag should be thin, not bulky so I would prefer avoiding an active tag unless I don't have a choice.

As much as possible, I'm trying to keep the reader compact, preferably can fit in a 2x4 inch enclosure that is also only about an inch thick.

Any suggestions?

Thank you.

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  • \$\begingroup\$ What about the tag - what do you have in mind? What operating frequency have you looked at? 2x4 for the reader is tiny - does this include the antenna? BTW suggestions aren't really answers so you may wish to try and focus the question a bit more and also provide some backbone to the application. \$\endgroup\$ – Andy aka Apr 11 '14 at 20:35
  • \$\begingroup\$ Thanks Andy. I am hoping for the tag to be as thin as possible, something like alibaba.com/product-detail/…. Operating at 125khz is the most common (and cheaper) but again the challenge is getting the range. The dimensions for the reader would be to try and get it as portable as possible, connecting to a mobile phone via the ear plugs so that a mobile app can then run additional functionality when the tag is detected. Yes the antenna is included. I am fairly new to RFID so I am hoping for some guidance. \$\endgroup\$ – pb32 Apr 12 '14 at 14:56
  • \$\begingroup\$ I only care about being able to detect the tag once the reader is within that 50cm range. Essentially it's like your typical EAS system. Put a tag on something and once that tag passes the reader, it triggers a function. In this case, it's the tag that's stationary, not the reader, and the reader can't be as big as the common EAS readers. Thank you! \$\endgroup\$ – pb32 Apr 12 '14 at 14:59
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50cm is more than doable with UHF EPCglobal Class 1 Gen 2 (ISO 18000-6C) RFID Tag. These operate in the 870-930 MHz ranges, depending on area of operation. These are actually made to be read at a distance.

A folded dipole tag with decent read range (assuming it is not next to metal) would be about 1.5-2" long and 0.5-0.75" wide. We are using an RFID chipwith an PCB antenna that is around this length and getting +1m read lengths.

Read range is over a 1m with a fairly low powered reader. You have to get polarization of the antennas aligned, or use a circularly polarized reader antenna. We have seen some pre-made serial reader modules that are 1"x1" or close to that. A reader antenna inside 2"x4" is tight, but for only 50cm most likely doable.

There are also some EPC Gen2 readers available now that function like the Square credit card reader, using the mic input as the data line. Here is one of these guys: http://thinkify.highwire.com/product/arete-pop-rfid-dongle-reader

For an embedded micro type application, I would go with the easy to interface with serial controlled modules.

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