Long-Range RFID With Feedback

Not long ago, we published an article about researchers adding sensor data to passive RFID tags, and a comment from a reader turned our heads to a consumer/maker version which anyone can start using right away (PDF). If you’re catching up, passive RFID technology is behind the key fobs and stickers which don’t need power, just proximity to the reader’s antenna. This is a much “hackier” version that works with discrete signals instead of analog ones. It will not however require writing a new library and programming new tags from the ground up just for the user to get started, so there is that trade-off. Sparkfun offers a UHF reader which can simultaneously monitor 25 of the UHF tags shown in this paper.

To construct one of these enhanced tags, the antenna trace is broken and then routed through a switching device such as a glass-break sensor, temperature limit switch, doorbell, or light sensor. Whenever continuity is restored the tag will happily send back its pre-programmed data, and the reader will acknowledge that somewhere one of the tags is seeing some activity. Nothing says this could not be applied to inexpensive RFID readers should you just want a temperature warning for your gecko terrarium or light sensor to your greenhouse‘s sealed controller.

Thank you, [Mike Massen], for your tip on RFID Doing More Than ID.

24 thoughts on “Long-Range RFID With Feedback

  1. The button solution is exactly what the RFID Buttons on the back of my phone are doing. I have been using them for 3 years now. They are called Dimple.io. RFID/NFC I don’t see the difference. Completely passive.

    1. Sjaak has it exactly right. One is basically radio, the other is basically a transformer. So it depends at what level you are working with them on.
      The two work on completely different principles even though at a high enough level they can have the same function.

      It’s like oLED and LCD, two very different technologies even if at a high enough level both can be used to display a picture of your cat.

  2. This design looks like it could be shrunk down further as dielectric resonator antenna. – Last time that I saw that someone presented RFID war-walking the naysayers in their infinite wisdom said that surely you would notice someone pointing a courier bag at you. Their memory of how mobile phones used to have visible antennas is short…

  3. In the early 1980s I experimented with 10 GHz Gunnplexers. Gunnplexers were basically police radar units with an extra tuning varactor stuffed in the resonant cavity. This enabled a ham radio enthusiast to tune across the 10 GHz band. This notion was an updated method used by many people used for microwave communications with klystrons and coffee cans in the late 1950s.

    One of the neat features was the notion of a retro-reflector with a diode on it. That diode could be powered on and off at fairly high frequency (the example from the Gunnplexer Cookbook was 30 MHz) and this could be received by the same or other Gunnplexer Transceivers. It was exactly the same concept as the long range RFID presented here.

    I had always realized that I could easily modulate that 30 MHz retro-reflector diode to include all sorts of telemetry. I was mainly interested in more precise distance ranging to the retro-reflector. I had thought of using spread spectrum sequencies to identify individual targets and to chirp the frequency of the 10 GHz transmitter to determine the range. There are lots of really interesting things one can do with this technology. But then life got in the way and the experiments went on the shelf.

    It seems that others have rediscovered this notion. Have fun with it. There is a lot more to it than you might first think.

  4. Kandi, honey, you just posted a reply while exploring the very realm of the beast you’re warning us about, at 3:16 AM, to an article about RFID/NFC technology – You really shouldn’t be skipping your meds like this.

    1. Not only would that make it more secure, but if you have two NFC cards in the same wallet, you could decide which one you wanted to use without interference from the other.
      I know the convenience is that you can just mash your whole wallet up against a store’s reader, but I think a lot of people who frequent this site would trade that convenience for security. I certainly would.

  5. I have seen a somewhat similar approach used in Class 3 Surge Protection Device cartridges. Instead of providing a switched contact for monitoring the health status of the SPD, one or more RFID coils are connected in series with a thermal fuse. In the event of a surge, the heat from the MOV cases the the thermal fuse to open and disable the RFID. The SPD I discovered this in had two RFID units with different tripping thresholds.

    1. The problem is that the SPD can not be monitored unless scanned with a handheld reader periodically unless a specialized SPD monitoring device is installed with a bank of SPD units.

  6. In the spirit of this community I feel I should point out that despite the economy of the tags and sensors the IMPINJ reader that is used here is ~$1,500 (without the long range antenna). A link to an alternative that is better suited to the collective of HACKADAY would paint a better picture for those that can’t readily see the viability of this in their hobby level projects.

    1. It’s ok, My hobby-level projects never live beyond the first manic prototyping session. At some point reality sets in (or comes home earlier than she said she would) and I have to re-assemble the vacuum cleaner.

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