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rfid wildlife monitoring project

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juannim View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote juannim Quote  Post ReplyReply Direct Link To This Post Topic: rfid wildlife monitoring project
    Posted: 07 February 2012 at 1:08pm
Long post.  I apologize.  Looking for help/input/info/suggestions.  I am trying to help my wife (we are both researchers at a small university) develop a RFID method for collecting data on bird roosting.  I have some very basic EE knowledge, but am having to learn this stuff mostly from the ground up, and am fairly bewildered by all the info out there.

Our birds sleep in groups of up to 10 in small bird "houses" during certain times of the year.  Other groups have posted wonderful directions for constructing extremely cheap homemade datalogging systems for RFID proximity readers based on lightweight (less than 0.15 g) implantable LF tags, a cheap atmel RFID reader IC and a cheap microcontroller IC: (http://www.animalmigration.org/RFID/cheapRFID.htm)

Their whole design is ~$25 (plus graduate student labor) and would allow us to deploy over our entire (100+ location) data collection area were it not for two problems:
1) We need to be able to detect more than 1 tag in range at a time (or detect them all sequentially within a few seconds, with measurements taken every 2 minutes or so, perhaps much less frequently)
2) We need to have ~10 cm of reading range, not the ~1 cm that is probably possible with their setup

To address problem 1, it seems that we need to use anticollision tags, then design the reader to detect collisions and then execute a tree-walking algorithm.  I realize that there are commercial setups out there that do this, but they are prohibitively expensive and don't allow for remote (battery-powered) datalogging deployment.  So far, the only LF, anti-collision, implantable transponders that meet our weight limits seem to be Hitag S tags.  I was hoping that there might be a low-level IC set that would do the collision detection automatically, then signal the microcontroller, which would then implement the tree-walk, but I can't find anything.  I am looking at the Hitag HTRC110 reader chip, since I don't even know if any other reader IC's would be compatible with their transponders.  I understand how the tree-walking algorithm works, but don't know how to physically know (from the modulator output) when there has been a collision?  With my limited understanding, I don't see how to detect the collision with their reader IC.  Is the collision detection stuff pseudo-proprietary, and thus not available to the uninitiated like me via internet?   

Problem 2 seems more soluble, perhaps some properly tuned amplifiers driving the antenna and ferrite placement to extend the range in one direction.  

So, I am looking for suggestions for how to attack this problem.  Any enlightenment is appreciated. Thanks.  Jonathan
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amal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2012 at 3:25pm
I would avoid HITAG and go with an EM family tag and reader IC that both support anti-collision. The microproc would not likely need to do anything but listen for tag IDs to stream in, and possibly do some duplication elimination in RAM before logging into NVRAM or whatever storage you'd be implementing.

Check here for more info on EM products; http://www.emmicroelectronic.com/Line.asp?IdLine=3

If you want to go with LF, the EM4095 IC is your ticket. Otherwise, for HF there is the EM4094. I'm pretty sure both support anti-collision, but you might want to ask their pre-sales or tech support for more info... and you'll need to ensure the tag types you want to use also support it of course.

Have you considered leg tags? They are little leg "anklets" that snap on instead of getting implanted. They come in LF and HF versions, and you'll likely have an easier time reading those tags than dipping into the LF range to read an implant that is embedded in interference inducing flesh.
Amal ;)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote juannim Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2012 at 3:55pm
Thanks for the info.  I will read some more about the em family.  The big deal for us is the weight.  I actually looked into those leg tags initially, but they are too heavy for our tiny little songbirds.  I need to find an EM transponder that is ~0.1 g, which is about what a 2 mm x 12 mm glass-encased implantable tag weighs in at.  So, the em family will only work for me if I can find supplier for the glass-encased form factor.  We won't actually implant the tags, but will work out some kluge to clip the encased ones to their legs.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2012 at 9:43pm
Ahh, makes sense. I saw some other small bird tracking systems setup using small glass tags that were banded to the leg using a light-weight paper tube and a dab of superglue. Not sure how long those were designed to stay affixed, but I'm sure they were light.
Amal ;)

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