Wheelchair proximity detection

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.

"David Norwood" wrote:

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 >I need to trigger an automatic door opener when my wheelchair is within

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...

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

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

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.