125 khz reader active component

Well, first check out this post: http://www.rfidtoys.net/forum/forum_posts.asp?TID=191&PN =1

On the USB based Phidgets reader, the chip that actually does the reading is an EM4097 which reads the EM41xx family of RFID tags. But, to get the range you're looking for, you'll have to build your own reader from scratch. Read range has a direct relationship to the combination of factors:

- output power the reader can push into the antenna, which in turn creates a large enough magnetic field to energize the tag at larger distances

- antenna shape and size (for the same reason above)

- reader components with enough sensitivity and signal pre-processing to be able to "hear" the tag's return signal without drowning it out by pushing too much power through the antenna

- finally, the tags themselves are an important component, particularly the tag antenna design. It takes two to tango, and it takes a coordination of both reader and tag to achieve very long ranges at 125KHz.

Buying a commercial long range reader will probably be easier and cheaper than trying to construct your own... but you can probably save money by building your own controlling circuitry and writing your own software for your RFID based project or solution.

MikelMD wrote: Then I will embark on the controller and software (path of least resistance). Any pointers on the controller creation?

I would probably look at buying one of the cheap parallel port or serial port controllers I referenced here: http://www.rfidtoys.net/forum/forum_posts.asp?TID=202&PN =1

If you want to build something that does not require a PC, then I would look at using microprocessor like a Parallax STAMP module. Those have several I/O pins you can use to read data in from various RFID reader modules. You can then connect a serial based controller board to the microprocessor through a single I/O pin in order to control up to 8 different relays. Of course, you can control relays directly with the STAMP microprocessor's I/O pins, but I assume most of those pins you'd want to use for data input from different readers.

If you are going the PC route, and you really don't want to spend money on a relay control board, you can build your own using the parallel port. There is a wealth of information out there regarding the wonders of the parallel port... a great place to check out is this amazing site called ePanorama, specifically this page about the parallel port (pdf).

Alternatively, you can check out this book called "Controlling The World With Your PC"... I read it a few years ago and it opened my eyes to the simplicity of using various ports on my computer to manipulate, and in some cases, sense the outside world. Even though most computers don't have joystick ports anymore, their ability to convert analog signals to digital values that were easily read in almost every programming language was simply amazing to me. It comes with some example source code and pre-compiled programs as well. Well worth the read.


Edited by amal - 20 February 2007 at 1:19pm

Brett wrote: Can a passive tag be modified to make it a semi-active tag to increase the range (or decrease tag antenna size)?

Hmm, well, I seriously doubt you'd want to modify a tag yourself... but if you have the gear and smarts, then anything is possible. A semi-active tag is basically a switched active tag where the passive "ping" from the reader results in an active "pong"... the only issue is going to be able to "ping" that tag using a passive reader. That means you'll basically be facing the same range issue you'd be facing using all passive tags.

One thing you can't do is decrease the size of a passive tag by making it semi-active... the antenna size might be smaller, but you'll add a lot of bulk by needing to add a battery or some other power source to power the active portion of the tag. Also, you'll still need a large passive antenna to receive the "ping" from the passive reader.

You'd probably be better off just creating an active tag. Depending on your application, you might not even need an "RFID" style tag and reader pair... you might just be able to get by creating a typical RF telemetry style device and simple receiver.