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Bluetooth Transponder Chip

A self powered radio transmitter.
  (+1, -2)
(+1, -2)
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Inspired by pottedstu's comment on 'Bluetooth Wristwatch': "The power consumption for bluetooth is not negligible. I don't think the battery life would be too great. But if you can live with that, fair enough." A fair point.

I'm a firm believer that technology has to be practical before it can be adopted and a watch that needs charging up overnight just so that can set its time when you walk past a clock is not going to catch on.

Enter the bluetooth transponder chip. This would be a very short range bluetooth device that would power itself from the radio signal received by the base station and would feebly transmit its terse reply. The base station would probably have to have to be engineered to support unpowered transponders with a very effective antenna and sensitive circuitry to detect and understand the neccessarily low powered responses.

The chips would be embedded in other devices: watches, thermometers, secutity passes which would gain on battery life by not having to power the bluetooth transmitter.

Further devices could be developed with low power needs where the bluetooth chip would soak power out of all bluetooth (and possibly other radio signals) powering the whole device. This could lead to a range of short range radio devices that would not need batteries: Bluetooth socks (not only capable of locating their other half but of telling you when they were last washed), Bluetooth solar radiation sensing necklace/sunglasses/beachtowel that tells you (via your organiser) not only when you've had too much sun but when the Germans are about to nab the sunbeds, etc etc etc, yada yada yada, bla bla bla.

st3f, Aug 09 2002

Bluetooth Wristwatch http://www.halfbake...etooth_20Wristwatch
The spark for this train of thought. [st3f, Aug 09 2002, last modified Oct 05 2004]

The New Generation of Payments http://www.wireless...tionofpayments.html
Discusses current transponder short range radio developments and applications. [Aristotle, Aug 09 2002, last modified Oct 05 2004]

Indala - Access Control Cards using the same principle http://www.indala.com
[BinaryCookies, Aug 09 2002]


       It may not be strictly BlueTooth but there are transponder short range radio developments in the pipeline [see link]. This is a whole field of research that I dipped my toes into recently.
Aristotle, Aug 09 2002

       Damn I need those socks...
yamahito, Aug 09 2002

       <Sigh> mumble mumble ..... radiated field strength ..... munble mumble ...... inverse square law ..... mumble mumble ..... forward gain ..... mumble mumlbe .... non-isotropic antenna pattern ..... mumble mumble .... near field, far field ..... mumble mumble.   

       This is Baked in the form of existing RFID passive (semi-active) tag technology, like the ID chips for pets. The base station needs to pump out a lot of power to make the tags operate, beyond that defined in the Bluetooth spec. Basically, this isn't a Bluetooth app within the meaning of the spec, but Aristotle is right that it's very much an active development.   

       Sadly, I don't think I can award a croissant because there's so much prior art.
8th of 7, Aug 09 2002

       //Bluetooth socks (not only capable of locating their other half but of telling you when they were last washed), //
Shouldn't that be Bluenostril?
thumbwax, Aug 09 2002

       <GROAN> "And with that, the case of the Crown vs. Thumbwax was proven, and he was hung by his Blueneck until he was dead." (And Blue in the face).
8th of 7, Aug 09 2002

       8th, Aristotle: it seems I'm in the presence of people who know *much* more about this than I do. I've looked up a little on RFID stuff and a few questions that none of the sites seem to answer. I hope that one of you can enlighten. If not, don't worry, I'll keep digging. Here goes:   

       Rule of thumb: what kind of signal strength drop-off would you expect on a reply from a passive RFID?   

       Has anyone ever used *passive* RFID to generate a dynamic response ie the radio signal powers some computation as well as the return signal?
st3f, Aug 09 2002

       Dammit! I was just going to post an idea almost identical to this, and here I find you beat me to it by over a year. Ah well, have a bun.
krelnik, Sep 24 2003


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