Archive for March, 2009

Rfish Reader Prototype

March 30, 2009

Motivated by the success of linking a BlueSmirf Bluetooth module directly to the Parallax RFID reader I began to think about how to package the reader in a way that allows you to use it close to or even in the water. A visit to the local DIY store brought up a cable junction box by Ensto, a Finnish company. Intended to shield high voltage electric installations from dust and humidity, the practically water-tight box comes in clean Scandinavian design. It includes an ergonomic front shield with rounded edges and rubber “buttons” on the side and costs no more than $3.

Ensto Box

Unfortunately, the Parallax reader does not fit into this little box. Convinced that it is pretty ideal to embody the first Rfish reader, I thought about cutting the Parallax shield between the antenna and the reader logic to squeeze it in. Meanwhile the ID-12, a small RFID reader module with built in antenna for only $29.95, arrived from SparkFun. With the previously gained knowledge, the hint from a squid and a soldering iron (d0 to rx-i, /rst to 5v to vcc and fs to gnd to gnd) it was possible to coax the ID-12 into sending the first ID to my laptop via Bluetooth in half a day. And even better: It’s a perfect fit.

Rfish Reader v0

A first test in the kitchen sink seems to prove that both RFID and Bluetooth perfectly work when the box is floating in the water and even when it is submerged a few centimeters. What’s still missing is a sort of feedback in the form of a buzzer or a vibrator, a power switch and maybe a stronger battery (though it has been on for hours now and keeps working flawlessly). Still, I guess we can call this a major milestone without exaggeration.


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Jumping In At The Deep End

March 4, 2009

To gather some hands-on experience with RFID technology, and to eventually build a first prototype of an Rfish reader, I did order Grand Idea Studio’s Serial RFID Module which is available as item #28140 from the Parallax web store for $39.99 (discounts apply for orders of five or more). From an earlier project I have a BlueSmirf Gold Bluetooth Module, sold by SparkFun for $64.95 and an USB to Serial Adapter similar to the FT232RL for $14.95, SparkFun as well.

After reading the Data Sheet of the the Parallax module it seemed that some additional circuitry is necessary to connect the 5V RFID reader to the 3.3V BlueSmirf module. Lacking even the most basic hardware skills I thought that this could already be the end. Google brought up several projects connecting an RFID module to a Laptop or a controller like the Arduino, but only after a while I found Knut’s Bluetooth RFID reader, the project by HC Gilje and some comments hinting at a similar effort by David from Blendid. Thanks to their encouragement I had another look at SparkFun’s product page and finally realized that the BlueSmirf module can be powered from 3.3V up to 6V for easy battery attachment. So all there was left to do was setting the BlueSmirf to 2400 baud and throwing together a test program that reads from the COM port. Half an hour later the console on my laptop displayed the first few RFIDs – received over Bluetooth, straight from the Rfish reader.


The Parallax Serial RFID module and the BlueSmirf Bluetooth module where connected through direct wires (sout to rx-i, /enable to rts-o, vcc to vcc and gnd to gnd) and powered by the same battery pack (three AA LR6 1.5V cells). While this might not be the ideal setup it is at least a proof of concept. Once again it paid out to eliminate the biggest risk first – today was a good day.


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Your Daily Serving

March 3, 2009

The remaining part of the reference model we haven not looked at yet is the Rfish server. You might ask yourself why a simple lap counter should be connected to the internet at all. But if you swim more often than once a month you might well be interested in the history of your lap counts visualized as a fancy trend chart right in your web browser. Also, sending the link to your current high score to a friend might be a fun way to compete, even if you swim in different towns. Or maybe you would want to automatically publish your lap count on Twitter after every session?

Whatever your needs, once the lap count data is available on the web in a standard format like RSS, there is almost no limit to what can be done with it. This statement will of course alarm advocates of privacy. But even if the exact mechanism of how to store data on the Rfish server is not clear yet we can limit possible damage by simply not storing any personal data such as the name or email address of anybody. The only link between you and your data will be the number stored in your RFID tag. The lap counts per tag are public but you decide if you want to publish which tag is yours.

Image by Pixelsior

The mother of all Rfish servers is online at already (albeit with rather limited functionality) but the system does not require a central server. Once the development phase is over, it should be possible to clone the server and run a separate instance. As long as the links to the Rfish community sites remain in place on the start page of every instance, users will be able to lobby for new features and to share tutorials for setting up everything and building additional Rfish reader hardware. In the case of a design decision affecting more than a single Rfish component, this blog shall retain the authority to guarantee the conceptual integrity of the overall system architecture.


Creative Commons License This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Switzerland License.