Wheelchair proximity detection

[David Norwood]

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.

- 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.

David

[David]

Hello David,

On Tue, 1 Aug 2006 00:57:14 UTC, "David Norwood" <judapeno@gte.net> 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

[Dave Houston]

Did you specify "proximity" because you're unable to operate a switch?

If you can operate a switch, there are several RF kits (some with security
codes) that will operate a relay (or relays). They would seem to be ideal
for this. Here are a few (about half-way down the page)...

http://store.qkits.com/category.cfm/RF

"David Norwood" <judapeno@gte.net> 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.
>
>- 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.
>
>David
>

[Robert Green]

"David Norwood" <judapeno@gte.net> 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.

[David Norwood]

"Dave Houston" <nobody@whocares.com> wrote in message
news:44d03f73.1213516265@nntp.fuse.net...
> Did you specify "proximity" because you're unable to operate a switch?

Yes, I am paralyzed below the neck. I could operate a switch with great
difficulty. A proximity detection system would be much easier if it worked.

David

[AZ Woody]

Could something like an IR beam break be used? When the chair breaks the
beam, the door opens..

Or how about an ultrasonic type sensor. Something like the have on the
doors to some stores, that opens the door when someone approaches.

"David Norwood" <judapeno@gte.net> wrote in message
news:0TQzg.7223$jt.5810@trnddc04...
>
> "Dave Houston" <nobody@whocares.com> wrote in message
> news:44d03f73.1213516265@nntp.fuse.net...
> > Did you specify "proximity" because you're unable to operate a switch?
>
> Yes, I am paralyzed below the neck. I could operate a switch with great
> difficulty. A proximity detection system would be much easier if it
worked.
>
> David
>
>

[David Norwood]

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@United.Com> wrote in message
news:rOdGr40LMPU3-pn2-xzSK84lFZHv1@localhost...
> Hello David,
>
> On Tue, 1 Aug 2006 00:57:14 UTC, "David Norwood" <judapeno@gte.net> 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

[David Norwood]

"Robert Green" <ROBERT_GREEN1963@YAH00.COM> wrote in message
news:0Z6dnW1KlNhlxFLZnZ2dnUVZ_sydnZ2d@rcn.net...
> "David Norwood" <judapeno@gte.net> 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.
>

[E. Lee Dickinson]

"David Norwood" <judapeno@gte.net> wrote:

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

There are a number of component-level voltage regulators that would do the
trick nicely, if someone in your house is handy with a soldering iron.
Beyond that there plenty of pre-packaged DC/DC voltage converters. A wire to
each side of the battery, and the other side has regulated +5vdc. "dc
voltage converter" as a google phrase reveals plenty, a search of some
surplus sites (www.alltronics.com for example) would probably yeild more.

[David Norwood]

I want something that just triggers with my wheelchair.

David

"AZ Woody" <Reply@here.not.email> wrote in message
news:44cfdbdb$0$506$815e3792@news.qwest.net...
> Could something like an IR beam break be used? When the chair breaks the
> beam, the door opens..
>
> Or how about an ultrasonic type sensor. Something like the have on the
> doors to some stores, that opens the door when someone approaches.
>
> "David Norwood" <judapeno@gte.net> wrote in message
> news:0TQzg.7223$jt.5810@trnddc04...
>>
>> "Dave Houston" <nobody@whocares.com> wrote in message
>> news:44d03f73.1213516265@nntp.fuse.net...
>> > Did you specify "proximity" because you're unable to operate a switch?
>>
>> Yes, I am paralyzed below the neck. I could operate a switch with great
>> difficulty. A proximity detection system would be much easier if it
> worked.
>>
>> David
>>
>>
>
>

[Dave Houston]

"David Norwood" <judapeno@gte.net> wrote:

>
>"Dave Houston" <nobody@whocares.com> wrote in message
>news:44d03f73.1213516265@nntp.fuse.net...
>> Did you specify "proximity" because you're unable to operate a switch?
>
>Yes, I am paralyzed below the neck. I could operate a switch with great
>difficulty. A proximity detection system would be much easier if it worked.

How about a sip & puff switch? How do you control the chair?

I would not use a small battery powered device. You might find yourself
"locked out" by a dead battery. Ideally, you need something like a barcode
scanner powered by the household wiring with the barcode on the chair.

[Dave Houston]

"David Norwood" <judapeno@gte.net> wrote:

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

A linear regulator chip (e.g. LM317) can handle this for less than $1.

http://www.mouser.com/search/refine.aspx?Ntt=lm317
http://www.st.com/stonline/books/pdf/docs/2168.pdf

[AZ Woody]

"David Norwood" <judapeno@gte.net> wrote in message
news:tVRzg.7243$jt.69@trnddc04...
> Is there a < $50 module that converts 24 vdc to 5 vdc?

Not really a "module", but a lm7805 voltage regulator (three pin - Vin,
Vout, GND) will give you a steady 5v. Depending on current requirement,
they can be had for about $0.25, and at most are about $1.

[David Norwood]

Is it really as simple as connecting the input and output voltage wires to
this one chip, or do I have to design a circuit around it (which I don't
know how to do)?

David

"Dave Houston" <nobody@whocares.com> wrote in message
news:44cff736.1260558828@nntp.fuse.net...
> "David Norwood" <judapeno@gte.net> wrote:
>
>>Is there a < $50 module that converts 24 vdc to 5 vdc?
>
> A linear regulator chip (e.g. LM317) can handle this for less than $1.
>
> http://www.mouser.com/search/refine.aspx?Ntt=lm317
> http://www.st.com/stonline/books/pdf/docs/2168.pdf
>

[AZ Woody]

With a LM7805, it's one device (not always a chip), as the Lm7805 is
available in a to220 package. Two wires to one of the 12v bats, and two
wires at 5v. The Lm317 will require a few more parts.


"David Norwood" <judapeno@gte.net> wrote in message
news:EjTzg.7273$jt.6679@trnddc04...
> Is it really as simple as connecting the input and output voltage wires to
> this one chip, or do I have to design a circuit around it (which I don't
> know how to do)?
>
> David
>
> "Dave Houston" <nobody@whocares.com> wrote in message
> news:44cff736.1260558828@nntp.fuse.net...
> > "David Norwood" <judapeno@gte.net> wrote:
> >
> >>Is there a < $50 module that converts 24 vdc to 5 vdc?
> >
> > A linear regulator chip (e.g. LM317) can handle this for less than $1.
> >
> > http://www.mouser.com/search/refine.aspx?Ntt=lm317
> > http://www.st.com/stonline/books/pdf/docs/2168.pdf
> >
>
>

[Dave Houston]

The circuit is simple and you would know how to do it if you had read the
datasheet I referenced. ;) It's pretty simple stuff.

"David Norwood" <judapeno@gte.net> wrote:

>Is it really as simple as connecting the input and output voltage wires to
>this one chip, or do I have to design a circuit around it (which I don't
>know how to do)?
>
>David
>
>"Dave Houston" <nobody@whocares.com> wrote in message
>news:44cff736.1260558828@nntp.fuse.net...
>> "David Norwood" <judapeno@gte.net> wrote:
>>
>>>Is there a < $50 module that converts 24 vdc to 5 vdc?
>>
>> A linear regulator chip (e.g. LM317) can handle this for less than $1.
>>
>> http://www.mouser.com/search/refine.aspx?Ntt=lm317
>> http://www.st.com/stonline/books/pdf/docs/2168.pdf
>>
>

[Dave Houston]

If done properly the 7805 will also require a few extra parts.

"AZ Woody" <Reply@here.not.email> wrote:

>With a LM7805, it's one device (not always a chip), as the Lm7805 is
>available in a to220 package. Two wires to one of the 12v bats, and two
>wires at 5v. The Lm317 will require a few more parts.
>
>
>"David Norwood" <judapeno@gte.net> wrote in message
>news:EjTzg.7273$jt.6679@trnddc04...
>> Is it really as simple as connecting the input and output voltage wires to
>> this one chip, or do I have to design a circuit around it (which I don't
>> know how to do)?
>>
>> David
>>
>> "Dave Houston" <nobody@whocares.com> wrote in message
>> news:44cff736.1260558828@nntp.fuse.net...
>> > "David Norwood" <judapeno@gte.net> wrote:
>> >
>> >>Is there a < $50 module that converts 24 vdc to 5 vdc?
>> >
>> > A linear regulator chip (e.g. LM317) can handle this for less than $1.
>> >
>> > http://www.mouser.com/search/refine.aspx?Ntt=lm317
>> > http://www.st.com/stonline/books/pdf/docs/2168.pdf
>> >
>>
>>
>

[AZ Woody]

Not as simple as a lm7805, right?


"Dave Houston" <nobody@whocares.com> wrote in message
news:44d00cf7.1266127750@nntp.fuse.net...
> The circuit is simple and you would know how to do it if you had read the
> datasheet I referenced. ;) It's pretty simple stuff.
>
> "David Norwood" <judapeno@gte.net> wrote:
>
> >Is it really as simple as connecting the input and output voltage wires
to
> >this one chip, or do I have to design a circuit around it (which I don't
> >know how to do)?
> >
> >David
> >
> >"Dave Houston" <nobody@whocares.com> wrote in message
> >news:44cff736.1260558828@nntp.fuse.net...
> >> "David Norwood" <judapeno@gte.net> wrote:
> >>
> >>>Is there a < $50 module that converts 24 vdc to 5 vdc?
> >>
> >> A linear regulator chip (e.g. LM317) can handle this for less than $1.
> >>
> >> http://www.mouser.com/search/refine.aspx?Ntt=lm317
> >> http://www.st.com/stonline/books/pdf/docs/2168.pdf
> >>
> >
>

[Robert Green]

"David Norwood" <judapeno@gte.net> wrote in message

<stuff snipped>

> 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.

I'm not sure how well these things can be calibrated, give the amount of
trouble my local Target has with supposedly deactived tags going off at the
exit sensor.

I've been looking at some unit at Ebay, particularly this kit:

* 13.56MHz
* Dimensions: (58mm X 34.5mm or 2.3”x 1.4”)
* Embedded antenna
* Read Range up to 75mm (embedded antenna), or 250mm (external antenna)
* Build in Multi Interface with Processors
SPI (up to 1Mbps) for high-speed application
Or RS232 with 9600-57600bps for long distance application
* 5V DC or Battery power for mobile operations. Power consumption as low as
7mA.
* Multi-protocol firmware enables read and write of ISO standard and Philips
Mifare Tag/Card.
* LED and BUZZER output for industry application.

The kit is listed at a starting bid of $50. You'd have to add an external
antenna and even with it, the range is only a foot. However, it may be
possible to mount the antenna near the door and low to the ground on one
side. Two different tags, each mounted on opposite sides of the chair,
could be used to determine if you are leaving (right tag detected - close
the door behind you, left tag detected,
your are outside approaching the door).

I'd look at my entryway to see if I could figure out whether I could conceal
the antenna close enough to the passing wheelchair that it came within a
foot. At my house, there's no way to approach the door without going
through a narrow porch opening made of brick. If I mounted an RFID antenna
there, it would almost impossible for chair-mounted tag to NOT get within
range.

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

Where do you want to mount the reader or its antenna? I am assuming inside
the house, on the other side of the door and that's why you need a
three-foot range. If you can rethink that requirement and find some way to
mount the unit to be close to the tag, you could use the much cheaper
passive RFID tags and eliminate the siphoning circuit.

I'd probably design a sensor swing arm that would almost act as a inverse
"curb feeler" and would deflect when the wheelchair edge hit it. The swing
arm would then follow along the edge of the chair and would swing back like
a saloon door to its original position once the chair has passed by. Mount
the RFID tag at the height of the sensor arm and it should get close enough
to activate it.

> > 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.

If used commercial equipment is anything like the incredibly marked down
MUXes Marc found, they only appear every few months or so. It might take
some serious searching via their email notification service to find the
right device. Anyone looking for a 100 Wasp employee tags will find them on
Ebay at about 1/10 the cheapest price I have seen anywhere else. You're
right, though, the descriptions are deliberately brief. Most likely to
avoid any issues about the item not being as represented. You have to do
the research, model number by model number.

> >> - 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.

That's pretty low security! Perhaps lower than you want to go. Not just
any moving thing can get into your house, true. But anything moving thing
with a magnet could.

<stuff snipped>

> >> 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?

Yes. That's the easiest part of the project. And with the enormous
capacity of wheelchair batteries compared to, say a 9 volt transistor
battery, siphoning off power from the chair batteries would be the way I'd
go.

There's an outfit:

http://www.rfidexchange.com/purchasing.aspx

That has a lot of pricing info. As you already know, active RFID stuff
clocks in at the "thousands of dollars" price point although they have some
readers listed for under $500 that will do the range you want. But not much
under that and it's not clear what else you might need to make it work.

It's very possible that if you contacted the PR department of one of the big
active RFID players and explained what you are doing that they would
contribute to the cost of the project. They might be more than willing to
help if they could get it written up in the trades. They might also see it
as a potential new market for active RFID.

--
Bobby G.

[Dave Houston]

2 caps, 1 diode vs. 2 caps, 2 resistors. Not a significant difference. And
certainly not worth hijacking this thread.

"AZ Woody" <Reply@here.not.email> wrote:

>Not as simple as a lm7805, right?
>
>
>"Dave Houston" <nobody@whocares.com> wrote in message
>news:44d00cf7.1266127750@nntp.fuse.net...
>> The circuit is simple and you would know how to do it if you had read the
>> datasheet I referenced. ;) It's pretty simple stuff.
>>
>> "David Norwood" <judapeno@gte.net> wrote:
>>
>> >Is it really as simple as connecting the input and output voltage wires
>to
>> >this one chip, or do I have to design a circuit around it (which I don't
>> >know how to do)?
>> >
>> >David
>> >
>> >"Dave Houston" <nobody@whocares.com> wrote in message
>> >news:44cff736.1260558828@nntp.fuse.net...
>> >> "David Norwood" <judapeno@gte.net> wrote:
>> >>
>> >>>Is there a < $50 module that converts 24 vdc to 5 vdc?
>> >>
>> >> A linear regulator chip (e.g. LM317) can handle this for less than $1.
>> >>
>> >> http://www.mouser.com/search/refine.aspx?Ntt=lm317
>> >> http://www.st.com/stonline/books/pdf/docs/2168.pdf
>> >>
>> >
>>
>

[Internode]

Hi David,

What is you floor made of? Could you put a IR transmitter into the floor
shining upwards?

Do you have any X10 equipment with say a W800 connected?

Neil.



"David Norwood" <judapeno@gte.net> wrote in message
news:KFxzg.3781$zV6.2418@trnddc03...
>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.
>
> - 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.
>
> David
>

[Dave Houston]

If you investigate, you may find that this problem has already been solved.
Try support groups for quadriplegia and for ALS and search Google on
"wheelchair accessibility". The site below has a "Wheelchair Chat" forum
where you might get better input than you'll find here.


http://www.apparelyzed.com/phpodp/odp.php?browse=/Health/Support_Groups/


"David Norwood" <judapeno@gte.net> 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:

[Dave Houston]

Powering any device from the chair battery _may_ void the chair warranty.
People I've worked with in the past (ALS victims and quads) have indicated
this is probable. The manufacturers have to be concerned about product
liability claims.

Most power chairs have two high torgue DC motors that will be
starting/stopping while you are positioning the chair for ingress/egress.
This will create a noisy electrical bus which any attached electronic
devices will need to deal with.

You will probably not find an active RF device that can transmit
continuously on small batteries for more than a matter of hours. At ISM
frequencies, the FCC prohibits continuous transmissions. Look at the mA draw
of the transmitter (4-5mA typical) vs. the mAh battery capacity.

I think this leaves only a switch operated transmitter (where small
batteries can give long life) or a passive device on the chair that
interfaces with some type of reader that is powered from the household AC
circuits. Unless the switch operated device also can warn of weak batteries,
you have a potential failure point.

I still like the concept of a barcode reader (or readers, if you need it
both inside and outside) with the barcode on the chair. Barcode readers
don't require precise alignment. A pressure mat or IR beam can activate the
reader(s). It also is relatively secure if only the barcode on the chair
will automatically open the door.

More esoteric and creepy, there are implantable, passive devices (Digital
Angel) that some have used for automatically opening doors. I haven't looked
at this lately but, as I recall, the range was a foot or two - it depends on
the reader.

"David Norwood" <judapeno@gte.net> 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.
>
>- 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.
>
>David
>

[Bill Kearney]

> 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.

From an entirely different angle, conside the "Man overboard" systems they
use on boats. They're designed to trigger when the sensor gets out of
range. Good for around 200 hours of battery life on the remote, apparently.
Something like one of those might be an interesting place to start if you
want to hack something...

[Kyler Laird]

"Internode" <somewhere@nothere.com> writes:

>What is you floor made of? Could you put a IR transmitter into the floor
>shining upwards?

IR seems like the obvious answer to me too but wouldn't it be much
easier and more effective to put the transmitter on the chair? It's
low-power, only triggers with the chair, and it can be directional so
that it only triggers when the chair is aimed at the door.

IR is so cheap and easy to use that I would expect it to be used for
lots of other applications after the initial need is satisfied.

--kyler

[Dave Houston]

I did a bit of googling and, as I expected, quickly found several available
systems that address this need. Most require a switch on the chair but they
have things like chin operated switches. Since you didn't respond to my
ealier question about how you control the chair, I don't know whether a chin
switch is appropriate but I think you'll probably have better results by
communicating with companies who make automatic door openers for wheelchair
access than you'll get here. Here's one link.

http://www.opensesamedoor.com/

"David Norwood" <judapeno@gte.net> 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.
>
>- 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.
>
>David
>

[David Norwood]

Sorry, I did respond to your question but accidently sent it to your
non-existant e-mail address. I drive my chair with a sip-n-puff. I could
interface an ECU with some sort of remote control for the door, but it is
tiring and time consuming to access the ECU functionality. That is why I'm
asking about proximity detection.

I am going to try a bluetooth device powered off the chair batteries.
Thanks to everyone who contributed ideas.

David

"Dave Houston" <nobody@whocares.com> wrote in message
news:44d22ecc.1405861296@nntp.fuse.net...
>I did a bit of googling and, as I expected, quickly found several available
> systems that address this need. Most require a switch on the chair but
> they
> have things like chin operated switches. Since you didn't respond to my
> ealier question about how you control the chair, I don't know whether a
> chin
> switch is appropriate but I think you'll probably have better results by
> communicating with companies who make automatic door openers for
> wheelchair
> access than you'll get here. Here's one link.
>
> http://www.opensesamedoor.com/
>
> "David Norwood" <judapeno@gte.net> 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.
>>
>>- 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.
>>
>>David
>>
>

[Bob Vaughan]

All this discussion ofRFID and IR has me thinking about a hybrid system..

Use a IR/motion sensor to sense proximity to the door area triggering a RF
transmitter. On the chair, a RF receiver senses the signal, and triggers
a second transmitter, which is received by the automatic door.

The system is only active when activity is sensed in the door area, and the
door is only activated when the proper RF signal is received. As an option,
the door receiver can be active fulltime, or only when activity is sensed.

On the chair, only the receiver is normally active, the transmitter is only
active when a signal from the door is detected.

--
-- Welcome My Son, Welcome To The Machine --
Bob Vaughan | techie @ tantivy.net |
| P.O. Box 19792, Stanford, Ca 94309 |
-- I am Me, I am only Me, And no one else is Me, What could be simpler? --