Henry Sazon

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10 years ago.

RFID system to detect a specific object 50 cm away

Hello,

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. 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.

The reader should be compact, preferably can fit in a 2x4 inch enclosure that is also only about an inch thick.

Is there such a solution I can work with?

Thank you.

yes,you can. you can buy rfid on this site: http://www.asiarfid.com

posted by nicholas kait 09 Sep 2016

3 Answers

David Lam
9 years, 4 months ago.

i think your RFID System need to calculate the (RF) communication link budget first(Transmission power and sensitive...etc.) , and limited on physical size~ if your design include antenna or particles be prototype(broad), i feel used software tools - ADS for circuit simulation, CST for the environment analysis. And i favorite SEMTECH chip to design, murata provide information to choice which suitable/acceptable surface mount components, others is your routing (matching Z...etc.)

Ref: http://ww1.microchip.com/downloads/en/DeviceDoc/51115F.pdf ....too many on Search google "RFID System Microchip"

(Are you having idea design on WiFi, blueTooth, NFC(maybe need correct to 50cm) ?) and i search in mBed have Silicon Lab, i also love it device in ISM band, but not wide...><

posted by David Lam 10 Dec 2014
Greg Steiert
9 years, 4 months ago.

I think you will have better luck reaching that distance with uhf rfid, especially if you want a passive tag solution: http://www.impinj.com/resources/about-rfid/the-different-types-of-rfid-systems/

Andy A
9 years, 4 months ago.

I'll second Greg's comment. Most of the RFID systems sold into the hobby market are short range systems in the kHz to low MHz region.

The UHF systems at 915MHz cost a little more but give far greater range and read rate. Basic tags are dirt cheap, a stickers with a tag in will cost a few pence or less depending on how many you get. Waterproof ones designed to attach to clothing and go in the wash are in the 50p range. Ones that work attached to metal objects may be in the £1 region.

The only problem you may hit is that you get too much range and detect things too far away ;-)

At max power (1W) ranges of 10m are easy, with a good tag and reader you can get about 50% reliability at 25m. If you only need 50cm then you can drop the transmit power right down which should also cut the cost of the reader, you can get lower power ones cheaper. However range can be very dependent on the environment, the relative angles of the tag and the reader etc... Generally I found that the range to get a reliable detection was about 1/4 of maximum range I saw. Using that as a rough rule of thumb a setup which always gets a tag at 50cm you may get the odd hit at 2m. Unfortunately due to the nature of RF signals there isn't a lot you can do about this.

You can make a guess at range based on signal strength but it'll be horribly inaccurate.

I'm not sure what you mean by "the signal can't be linear". Do you mean the RF polarization should be circular rather than linear? Or do you mean that the reader needs to be directional rather than omni-directional? The normal trick is to use a circular polarization antenna on the reader and the tags are linear polarization, it gives a slight range hit but minimizes orientation related problems. Directional antennas are easy as long as you don't need it too directional. A +/-60 degree patch antenna is fairly standard for this sort of thing.