Re: Wheelchair proximity detection

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"David Norwood" <judapeno@xxxxxxx> wrote in message

> 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.

A system like this would have to have some serious interlocking, I would
think, to prevent the door from closing inadvertently as well as keep it
from "fluttering" -opening and closing repeatedly - if you happen to be
sitting at the edge of the receiver range. It may mean you can't sit out on
the porch without the door going crazy. That's assuming a mode of operation
that's typical of some doors, but may notbe true of yours.

As mentioned, Velcro and a garage door opener eliminate those issues
although they do require enough mobiity to operate.  Someone could modify
one for you if that's a problem, so that the opener could be triggered with
a non-traditional activation methods.


> - it must work at about 3 feet.  I can't find an affordable RFID reader
that
> works at this range.

Have you checked Ebay for used commercial equipment?  Marc H. found a place
on the web that was selling video MUX's for about 1/10 the cost of a new
one.  (Thanks, Marc!)  Good deals abound if you know where to look and how
to get support from other than the vendor, who's probably just a liquidator.

> - 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?

Some that I have seen use a magnet inbedded in the pet collar.  A small
neodymium magnet can put out a field detectable from several feet away.
Hall-effect sensors allows contactless sensing of an external magnet or a
ferrous object.

http://www.allegromicro.com/hall/

Whether you could or would even want to use that for *your* door is another
question.  It is, however, how many pet doors work since they want the
"transmitter" part to be as cheap and passive as it can be.

Other forms of pet doors use IR in addition to magnets:

http://www.petdoors.com/cat_mate_electronics.htm,

> - 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.

Is this a power chair or a manual wheel chair?

--
Bobby G.