Re: Wheelchair proximity detection

["David Norwood" <judapeno@xxxxxxx>]

Thanks for your thoughts, David.  I have looked on ebay for commercial RFID
readers that work with active tags, but the listings have very little
information and google searches don't help much.  There isn't strong hacker
interest in active RFID tags yet.  I saw a recent post about the $12 G2
active tags that work with wifi.  It would be great if I could hack some
Linksys WRT54G routers to work with these, but I doubt G2 will release much
information about them since they want to sell systems.

David


"David" <FlyLikeAnEagle@xxxxxxxxxx> wrote in message
news:rOdGr40LMPU3-pn2-xzSK84lFZHv1@xxxxxxxxxxxx
> Hello David,
>
> On Tue, 1 Aug 2006 00:57:14 UTC, "David Norwood" <judapeno@xxxxxxx> wrote:
>
>> I need to trigger an automatic door opener when my wheelchair is within
>> about 3 feet.  I would like some sort of radio transmitter on the
>> wheelchair
>> and a receiver near the door.  Here are my requirements:
>>
>> - it must work at about 3 feet.  I can't find an affordable RFID reader
>> that
>> works at this range.
>
> Would you be able to operate a separate switch control?  I'm thinking
> of the transmitter-receiver units used for garage doors and car alarms.
> They are about $50 for both units.  The transmitter would need a 9VDC
> battery or perhaps a watch battery and last years.  You can also get
> multiple button versions.  Most are very easy to interface with by
> opening up the unit and soldering on your preferred switch.
>
> Another option is to reverse the transmitter-receiver location.  The
> transmitter would be at the door and trigger the low power receiver
> on your chair to respond with a signal.
>
> I've not read any of your other posts, if you've had any.  What do
> you consider to be cost effective?  Are the doors that you are
> triggering to open non-secure (inside) doors or entry ways to your
> home?  I'm thinking perhaps to have the sensor on the floor near
> the door on both sides.  It could sense your chair near the door.
> This could be anything from a magnetic sensor (very poor security)
> to RFID, optical scanner, or whatever might work for you.
>
>> - the transmitter must operate on a battery for at least two months
>> continuously.  I like Bluetooth, but can't find a low power transmitter.
>> What do they use on those automatic pet doors?
>>
>> - it must provide a simple contact closure, or have a serial or usb
>> interface and Linux drivers.  Zigbee?
>>
>> - I'm not too concerned about security.  There are easier ways to get
>> into
>> my house than spoofing a radio signal.
>>
>> - it must not require too much soldering.  I have friends that can help
>> with
>> this, but within reason.
>>
>> I've seen various radio transmitter modules on the web, but don't know
>> how
>> much power they require, and how to interface a receiver to my computer.
>> I've figured out how to do this with Bluetooth, but I have the power
>> issue.
>
> The automotive and garage door units are cheap and very low power.
> Most have security features to prevent spoofing.  Another idea that
> just occured to me is having the transmitter on your chair trigger
> with perhaps a 1/2 turn of one of the wheels.  Then all you need is
> to be approaching the door and retriggering it probably isn't a
> problem.  That also prevents keeping the transmitter on all the
> time.  Many of these transmitter-receiver pairs exchange codes
> when they recognize each other.  That way anyone that did record
> a signal while you were away from the house probably couldn't
> use it to get in later.
>
>> David
>
> A local accessibility group (perhaps if you have a customized
> chair or vehicle from them) could help with a cost effective
> solution.
>
> There is also the possibility of using a bar code scanner
> to read a code off the chair.  Scanners are perhaps $20-30
> and easily interfaced to a computer.
>
> I'll check out my reference books at work for ideas.
> You might also ask this question in comp.arch.embedded.
> They can at least address what Zigbee is good for and
> give you a few more ideas.  They might even be able to
> locate a used RFID device for you.
>
> Good luck,
>
> David