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RF TAG with LED ?

Hi,

I am trying to find a way to power multiple bi-color LEDs (lets call them 'led discs') from an RF field (no batteries in 'led disc') at close proximity to the receivers field antenna but at the same time have these 'led discs' uniquely identifiable for the purpose of independent control from a host system.

Control desired : led(s) on/off/flash for both anodes of the led.

So what i first thought was;

-RFID Tag CHIP (passive) 'led disc' uses a programmable RFID tag chip, which when receiving a specific command from an RFID host receiver/controller : lights/flashes the desired LED. Of course, the field would have to be quite powerful and also close proximity but that is not a problem. ( i have seen many examples flashing led's within RFID fields so i know the power at the proximity i want is available (in bursts perhaps), but none that i can find are independently controllable from the host system).

The problem with the above is as far as i can find, no RFID Tag chips have any programmable functions or IO (i suppose their isnt much need? But i have seen a few notes on people trying to do the reverse, and make passive rfid tags which collect and send their 'sensor data', be it a button or otherwise).

Now im looking at;

-Microchip RF series Looking at the Microchip 'rfPIC12F675K/675F/675H' series, it appears that these could be powered from a close proximity RF Field (operation

2 - 5 volts, very low current draw) as the controller in the 'led disc's, plenty of program space to play with for different 'flashes' etc, but they dont appear to both receive and transmit. But perhaps the RF Field which is powering the device could also be serving the signals. This is above my head here, and before i dive in, get samples and start playing - am i even heading in the right direction here ?

Then i have started to think about other more custom solutions. Moving away from RFID and i would love any suggestions for further research to keep me in the right direction.

Some background info here : the led discs dont need to be bright, only visible in ambient lighting. No batteries. Will initially be made in low quantities. Eventually individual costs should be somewhere under

20$ in parts which i imagine is more than enough room for the parts, and of course as small as possible :), i realise the antenna may be the limiting factor on size.

I have been pouring over a heap of RFID chip pdf's, both for the receivers and the tags, looking to see if there might be a way to accomplish the above but so far have not come up with anything solid.

So any ideas ? comments, suggestions ? :)

Cheers, Alex.

Reply to
Quack
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First pull up the legal limits of the field strength. Throw in the Q of the resonating circuit, and the amount of current required for LED to be seen and you'll recognize that it doesn't match.

The LED requires some 100uA but you only have uA.

Rene

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Reply to
Rene Tschaggelar

Surely there is enough power at legal levels and its only a matter of proximity ? what about;

- those sticky flashy led things you stick on a phone that lightup during a call

- i have seen casino chips which flash when within an RF field (at very close range of course!)

Alex.

Reply to
Quack

Have you tried to measure the amount of current available ??

Guessing is not good engineering.

donald

Reply to
Donald

Use a battery-powered tag.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

How can i measure it, i havent even decided how im going to do it. So, one of the requirements would be to make the necesary current available ... If its measured and not enough, something needs to change until it is: proximity, field strength, freq/atenna coil arrangements/tuning ...

Again, we have all seen led's light up and flash when close to a transmitter/rf field (mobile phone flashy badges etc), so there surely is enough current there in that scenario so its not impossible and this scenario is not so wildly different to what i have seen.

It depends how you would define 'guessing'. If i guessed that i could walk 10 metres away from the transmitter and still get the same effect, sure - fair comment. But im only wanting to replicate what i have seen with an added level of control, thats not a guess its a target.

I only want 20ma within a few centimetres of the transmitters coil atenna - i know that can be done, there are just plenty of variables to play with, especially that i am in control of both sides, being that the transmitter can also be as custom as required.

Saying all that, i know this is above my level here on the RF data side, but im sure i can get a good coupling between the RF coil antennas to get the power i need - and me being typically stubborn im still going to blindly stumble on and see how far i get :). Any help would be appreciated :)

Alex.

Reply to
Quack

I cant in this instance : and the battery would still need to be charged or replaced etc.

I have read some notes on a battery powered tag lasting 50 years, which occasionally flashes an LED during 'identification' comms : but this is not what i need. The LED must be able to be constantly on, OR flashing, OR off at the whim of the host controller.

Anyway, thought maybe that there was something out there already done (like an RF Tag IC with some io). Since noone mentioned it and i cant find it, i will have to play around with something more custom.

I will get some of the microchip RF ic's and see how i go with that, the problem i see with them is;

-receiving commands into the IC, how? If they are powered by the transmitters field, how can i also pull of some command requests coming frmo the transmitter? i bet it will get complex there :(.

-receiving commands back on the transmitter circuit to identify available discs within the field. I realize there will be a lot of collision problems :(.

So, assuming i will be pig headed and push down this road anyway - are these microchip RF chips a feasable option for this or is there something better suited ?

Alex.

Reply to
Quack

I don't off-hand see how you are going to couple enough power... UNLESS you have a HUGE antenna, and a BIG-ASS transmitter ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

I have seen it done in casino chips as well, passive tags. They use a pretty high frequency IIRC.

Reply to
The Real Andy

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