2009-09-19 @ 22:52
Ruby and RFID tags
It’s been forever since I’ve written a blog entry, so LETS DO THIS. I want to talk about reading RFID tags with Ruby. I am a nerd, so even though I can’t think of a good application, I am compelled to be able to read RFID tags. I love programming Ruby, so of course, I have to do this with Ruby.
Getting an RFID Reader
First thing to do, is buy an RFID reader. After searching around, I found the touchatag reader. I bought the touchatag starter pack. It’s only $40, USB, and comes with 10 RFID tags. Most importantly, it works well with libnfc (more about that later).
The tags that come with the reader have an adhesive back, so you can stick them to stuff. They also have the unique identifier printed on them so that you can make sure your program output is correct.
Interfacing with the reader
Now that we’ve got the reader, let’s do something with it! I mentioned earlier that the touchatag reader works with libnfc. Libnfc is a C library that knows how to work with NFC devices (nerd talk for “RFID readers”). I’ve written a gem called nfc that wraps up the C library in to something we can use in Ruby.
First thing we need to do is install libnfc. I use macports with OS X. With macports, installing libnfc is quite easy:
$ sudo port install libnfc
Installing on linux should be just as easy, but you’ll need to consult your package manager. Make sure to install the devel packages too!
After that, simply install the nfc Ruby gem:
$ sudo gem install nfc
Now that that is out of the way, we can actually read an RFID tag. Here is our code:
require 'rubygems' require 'nfc' # Find a tag NFC.instance.find do |tag| # Print out the tag we find p tag end
That’s it! Run the code, then touch a tag to the reader, and boom! We have output. With the tag I’m using, the output looks like this:
$ ruby -I lib test.rb (NFC) ISO14443A Tag ATQA (SENS_RES): 00 44 UID (NFCID1): 04 D7 62 91 21 25 80 SAK (SEL_RES): 00
The important part of this output is the UID field. That field is the unique identifier for this tag. The identifier comes back as a list of integers, but they are printed on the tag as hex. We can adjust the program just a little bit to see that list, or to get the same string that’s printed on the tag:
# Find a tag NFC.instance.find do |tag| # Examine the raw numbers p tag.uid # Get just the UID as a string puts tag.to_s end
The output looks like this:
$ ruby -I lib test.rb [4, 215, 98, 145, 33, 37, 128] 04D76291212580
That’s pretty much it. Unfortunately, I can’t think of anything fun to do with my tags, but maybe you can! I hooked my tags up to the “say” command that comes with OS X and made each tag say something different.
Non-Blocking NFC interaction
Our previous example blocked until an RFID tag was read. If you run the program without having an RFID tag on the reader, it will just sit there until it can read a tag. Sometimes we might want to tell whether or not there is a tag on the reader right now. In other words, we don’t want our program to block.
Calling find without providing a block will return immediately:
You’ll get a return value immediately. The tag returned will either contain a blank uid, or an actual UID. Here is the output run once with a tag sitting on the reader, and once without a tag:
$ ruby -I lib test.rb "04D76291212580" $ ruby -I lib test.rb ""
That’s pretty much it. Interacting with the touchatag reader is quite simple and straight forward. Currently the nfc gem supports reading ISO1443A tags (the tags that come with the reader). The reader should be able to read other tag types, but I haven’t had a chance to get other tags to test.
Touchatag provides an official API for their readers. But the API seems difficult and is dependent on a network connection.
Have fun reading some RFID tags!