RFID Reader Range

Posted by: @inq

I'm on my local public library board so nothing nefarious is going on.  Our library uses RFID tags in the books for checking out books and seeing if they walk out of the library un-checked-out.  In the last year or two, we've also done inventory using an expensive "system" that helps, but still has many flaws.  

I also head a Maker's Group at the same library and I thought this might be a cool project the group can tackle.

I'm wanting to learn more about RFID and have purchased the reader below.  It supposedly has a range of about 2 inches.  I want to be able to place it on the spine (while the book is on the shelf) and read the RFID tag in the book.  Unfortunately, people have placed them all over the pages and they may be at the furthest point from the spine... thus, they may be 8 inches or more away from the reader antenna. 

There are readers that have further range, but seem to jump up in price to several hundred dollars.  So a couple of questions come to mind:

1. Does anyone here have any experience using these?
2. Are there any hobbyist versions (about $20 or less) with a longer range?
3. Is it possible to increase the range of these hobbyist models?  Maybe using some hardware techniques to amplify things?  

 

"https://www.amazon.com/gp/product/B07SCY2LXB/"

https://www.amazon.com/gp/product/B07SCY2LXB/

@inq; all depends on what type of RFID tags and reader you have..most hobby RFID tags will be the passive type, mainly because their cheap, and the requirements of the amount tags being read, distance, and reader power that is required to enable the tags is low. Different Frequencies and reader output power(RF) is what will change the distance you can read that tags..With the Active types, since they are battery powered tags, they are much more expensive, but do offer longer ranges. I'm not an expert on RFIDs, nor have I had direct experience working with them outside of using them for inventory control of our equipment base at the plant. I used them to track my 4700 control valves, so we knew what particular valve was in service, where it was precisely, and other serial data. I had a very extensive Asset Management system of tracking them, specs, product info, repair data, even photos of the valves in the data base what showed whee they where located..ie, in the field, in the store room, or on a pallet ready to be shipped to a vendor for repair.

Sorry I couldn't help you with specifies of other hardware solutions to increasing your range to read the RFID's..  Maybe some other member has more experience with them can help...

regards,

LouisR

I'm sure the ones in the books are passive... fit inside a book - thin, and cheap.  I had the IT person that uses the reader go over it with me.  The antenna is a thin, rectangular, aluminum thing about 6"x8" that he slides in-between books.  It'll read about a dozen books total in both directions.  It will also read a couple of them if placed perpendicular to the books at the spines.  Obviously, the walk-through antennas at the exits don't care if they are even several feet away inside packs.

The reader above I have coming to play with probably won't cut it... why I'm posing the question.  I'll have to do more research on the frequency aspect.  I hadn't recognized that their were different frequencies involved.

I "think" I know that lower frequencies travel further, but higher frequencies provide more power to a passive device.  Seems conflicting benefits for distance requirements.  

VBR,

Inq

@inq AFAIK your 'think' is correct, like 2.4 and 5 WiFi.

@inq Indeed, all things are relative as you know by now..Yes the frequency thing is a bit confusing, but it has to do more with the combined impedance of both the capacitive and inductive elements of the circuits.

Remember, as frequency goes up in a capacitive circuit, the impedance goes down, (

XC=1/2πfC) and in an inductive circuit, as frequency goes up, reactance ( impedance) goes down Xl = 2πfL). the combination of the two reactance's equal total impedance, and this will affect the power output.

hope this helps explain the implied contradiction...Of course , nothing is as easy as it appears...because if that was so, everyone would be doing it!...lol

Regards,

LouisR

Posted by: @inst-tech

XC=1/2πfC) and in an inductive circuit, as frequency goes up, reactance ( impedance) goes down Xl = 2πfL). the combination of the two reactance's equal total impedance, and this will affect the power output.

Oh no... going to have to break out some books.  

@inq I cheated, I knew 5GHz carried more data but didn't travel as far as 2.4GHz.

Hi @inq,

  Sorry, I haven't played with RFID tech, but offer a few words for you to contemplate. No guarantees about the quality of the words, so treat as hints to research further, not 'facts'. And sorry, I only offering a few thoughts .. not a solution.

So here is my 'sermon' on the topic ... hopefully there wil be something of interest .. and maybe others with more radio experience can add a little more light.

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As noted in above replies, there are several frequencies used for RFID tags, and obviously any reader must match the tags it is looking for in that respect. The Amazon example you showed was for 125kHz .. I am not clear if you showed that because you knew it matched the tags you are looking to find, or just as an example of an RFID reader in the 'hobbyist' world .. perhaps you would like to clarify? (I am assuming you are not planning to replace all the tags!)

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The frequencies are 'dictated' on a semi-international agreement basis, as interrogating an RFID tag involves  transmitting a radio signal, so obviously they must be chosen to not interfere with the many other radio transmissions. Also, the power is transmission power is limited. For the small transmission powers involved with the products like the one you showed, the risk of the reader interferring with anything else is probably small and 'well understood' in the context of things like card readers, where the rfid tag must be brought very close to the reader, so the chance of anyone else being affected, is small.

Increasing the range of RFID detection, also increases the risk of causing interference. Whilst I would hope 'sensitive & delicate' stuff like heart pacemakers would be well protected, I have no experience or knowledge to determine when it might become hazardous. As I said above, these are only hints to research .. I am not making any claims or offering any 'advice'.

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Different frequencies are chosen to match different situations. Generally, the lower the frequency, the less it is affected by surrounding materials, but the larger the antennas need to be .. and the RFID tag itself must have its own antenna, which generally needs to be small enough to be 'inconspicuous' compared with the object is attached .. so for low frequency (125kHz especially), the practical RFID tag antenna is often small (compared to the size that would give good sensitivity), and hence the range is very short.

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The reader you showed from Amazon has little technical specification, and some very concerning reviews, so there is little to work with directly.

I suggest you try looking to the chip manufacturers for devices that could be used to build a new reader, if only for clues and background information. A very quick Google suggested Melexis and Microchip have some interests in RFID .. I am sure there are others.

Melexis offers a 'one 8-pin chip' solution for 125kHz (and also a very different chip for 13.56MHz).

Data sheet link at: https://www.melexis.com/en/documents/documentation/datasheets/datasheet-mlx90109

This includes a few comments:

This current resonance of the parallel antenna allows to build very low power reader base stations, contrary to serial antenna based versions. Readers using a serial antenna can leverage their voltage resonance to drive bigger antenna’s for long distance reading up to 1m, whereas the MLX90109 is designed to drive antennas to obtain a reading distance of 1cm up to 15cm (6”) (depending on efficiency and dimensions).

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13.2. How should I read data information from a transponder up to 15cm?
The reading distance depends on the complete system composed by the reader and the transponder. A reading distance with the MLX90109 transceiver up to 15cm has been demonstrated with a specific reader’s antenna (diameter = 130mm, Inductance = 44μH, Quality factor Qant = 87.2@125kHz) and a transponder with a credit card size antenna (80 x 50mm).

13.3. Is it possible to increase the output power of the MLX90109 transceiver?

<details>..The voltage on the antenna cannot be increased as it is limited by the power supply VDD...

<more details> ..

the MLX90109 uses the same connection (COIL ) for the transmission and the reception, it is not possible to use an external power transistor supplied with a higher voltage than VDD.

I wondered if the reader you found on Amazon was based on this device .. or a clone of it ... but this is pure speculation on my part.

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As the Melexis data sheet notes, a range of up to 1m is plausible, but expect to be building (or maybe buying) a 'more powerful' rig, possibly out of many discrete parts.

As a clue I spotted a coil antenna on RS website .. https://uk.rs-online.com/web/p/rfid-antennas/1262188

with a datasheet link that mentions..

The Micro RWD is designed to give up to 400ma pulse current with a peak voltageof up to 200v. This can give a 20cm read/write range with HT2 ISO cardtransponders.

I haven't taken the time to understand this, but it left me with the impression this is no longer a 'trivial' piece of equipment. Please read the original and draw your own conclusions.

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I have the impression your first target is to be able to detect the book on the shelf, in spite of some/many tags being placed far away from the spine. One consideration might be 'compromising' on the range ... if the number of books that have tags more than, say, 10cm (4") is modest, and it was possible to 'obtain/build' a reader that could cope with up to 10cm, then it might be more economic to retag the books with badly placed tags.

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You mention that some of the books are walking out of the library without being checked out .. clearly to detect these events, you would need to extend the detection distance to more like 1 metre ... or have you discounted that idea?

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Hope there is something helpful in all this verbage .. best wishes and good luck. Dave

@davee @Inq FYI, some alternatives are NFC, Bluetooth, and UWB. Have a look at Apple AirTags. 

Hi Ron @zander,

  Sorry, maybe I am missing something, but I don't understand how any of your suggestions would be used for detecting/auditing the presence of public library books.

I am presuming these library books are not 'high value, precious manuscripts', nor do they have a power source ... Which of your suggestions would enable tagging each book for a few cents?

Best wishes, Dave

@davee I have to admit I just assumed that buying from China in bulk would make the cost of NFC or BT chips inexpensive. AFAIK NFC is unpowered and I thought BT tags were passive as well. Not sure about UWB, that's a new one but I read that Apple is making use of it as part of the crazy expensive AirTags. I bought the equivalent tech several years ago to play with so I know the cost can be lower. One I didn't mention is QR but I discounted that since not all spines are big enough. Anyway, just tossing some ideas out there since there are issues with RFID.

@inq There is a typo error in my last post..XC=1/2πfC) and in an inductive circuit, as frequency goes up, reactance ( impedance) goes down Xl = 2πfL). the combination of the two reactance's equal total impedance, and this will affect the power output.

Xl = 2πfL, as frequency goes up , impedance goes up, as you can see by the formula. Sorry about that, I'll have to preview my post better before I post them..fat fingers gets me every time..lol

Regards,

LouisR

@davee - As usual, you give a very thorough treatise.  Considering your disclaimers, you've brought up more than one problem I had not considered and/or not yet researched.  

Aside - In my defense, I would have researched more diligently.  My current Internet capability has turned even more dire.  I am in an in-formal FCC complaint process and have started tracking my Internet capability.  Over the past 24 hours, I've averaged 12.7 kb/sec!  Remember the phone modem days when 57 kb/sec was King?!  A 5MB download took almost 2 hours.  A web page with pictures is a painful experience.  It works better in the A.M. as evident of my posts.

Back to our regularly scheduled discussion - In my very limited perusal of my Amazon options, it seemed there were three ranges... (1) NFC and having to touch or near touch (2) those in the several inch range (3) those in the several meter range.  Those in the last group jumped up to several hundred dollars.  Picking the one I did was solely in the price range and I assumed that having a separate antenna, might lead increasing the range... like adding an external antenna to an ESP8266.  That's the sum-total of my thoughts before pulling the Amazon trigger.

Another data point - The library has the portals for detecting books entering/leaving, so the book tags support long range detection, but we only need in the ~8 to 12 inch range.

Project Ambitions

As mentioned in the OP, my library Makers Group has just finished a project and are ready to sink their teeth into something more ambitious.  We also have varied interests.  Kids rabid to do robotics, others with 3D printing ambitions.  One group member brought in a few NFC tags and programmed them for the group with his phone. -- Thus, my solution to do a robot that can scan the books in the library, unattended.  (1) We'll study 3D CAD and design our own robot parts.  (2) Navigation in the very structured environment of a library is simplified (3) Scanning of the books, I assumed, would be the least of our troubles.

It won't be the first time my assumption will make an ass out of me. 🙄 😜 This might be too grandiose of a project.  

VBR,

Inq

Posted by: @davee

Hi Ron @zander,

  Sorry, maybe I am missing something, but I don't understand how any of your suggestions would be used for detecting/auditing the presence of public library books.

I am presuming these library books are not 'high value, precious manuscripts', nor do they have a power source ... Which of your suggestions would enable tagging each book for a few cents?

Best wishes, Dave

Exactly... the tags are already in the books.  They will not be replaced!  Now, I just need to find a cheap reader that can read the current tags.

Posted by: @zander

One I didn't mention is QR but I discounted that since not all spines are big enough. Anyway, just tossing some ideas out there since there are issues with RFID.

Actually, that is an option.  The books have a bar-code on the back of the book that has the exact same data as the RFID tag.  However, making a robot that can pull out each and every book to scan the tag on the back... is a FAR bigger problem. 😆