Re: Wheelchair proximity detection

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


.

Relevant Pages

  • Re: Wheelchair proximity detection
    ... I would like some sort of radio transmitter on the wheelchair ... and a receiver near the door. ... but can't find a low power transmitter. ...
    (comp.home.automation)
  • Re: Passive battery switch RFID
    ... Passive rfid transponders can be made with greater range than you have experienced. ... With IPASS you place the rfid in the center of your car/truck window and when you go through a toll plaza the reader induces an electrical current in the transponder. ... The power generated can be used to activate a transistor switch to provide power to the transmitter. ... You should be able to induce enough power in the unit to switch some kind of transistor switch connecting the battery to the second stage of the unit. ...
    (rec.radio.amateur.antenna)
  • Re: Keys for 2006 Sienna
    ... What about a spare transmitter? ... If you only need to open the door with the ... > Is there a separate key for the ignition and doors as in older cars or ... > to open the doors even if it won't start the car? ...
    (alt.autos.toyota)
  • Re: Need to build a remote controlled momentary switch
    ... Terry Pinnell wrote: ... >>I incorporated one, as a remote control, into a gag gift for the ... The controls on the transmitter, besides On-Off, are ... push the front door and back door buttons at the same time. ...
    (sci.electronics.design)
  • Re: Need to build a remote controlled momentary switch
    ... Terry Pinnell wrote: ... >>I incorporated one, as a remote control, into a gag gift for the ... The controls on the transmitter, besides On-Off, are ... push the front door and back door buttons at the same time. ...
    (sci.electronics.misc)