Re: Wheelchair proximity detection

["David Norwood" <judapeno@xxxxxxx>]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
news:0Z6dnW1KlNhlxFLZnZ2dnUVZ_sydnZ2d@xxxxxxxxxx
> "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.

As long as I can calibrate the sensitivity relatively accurately, I don't
think accidental door openings will be a problem.  I can stay away from the
door.

>> - 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.

See my other post about commercial RFID readers.

>> - 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,

Thanks for the information about the pet doors.  I didn't know they were
passive.  Maybe I can hack one.

>> - 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?

It's a power wheelchair, so I do have access to 24 volt power (two 12 volt
gel batteries in series).  It sounds like there are no radio transmitters
that can operate continuously off a small battery, so my Plan B is to attach
a Bluetooth device to my chair power.

Is there a < $50 module that converts 24 vdc to 5 vdc?


> --
> Bobby G.
>