Re: Wheelchair proximity detection

["David" <FlyLikeAnEagle@xxxxxxxxxx>]

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