On 21 Oct 00, at 18:50, Dr. Chris Kirtley wrote:

> I suppose by "a few feet" I mean at least one and preferably 5-10.

If you have 3 to 6 volts available at the device check out Microchip's
HCS412 secure transponder. When used as a powered tag, it can
be made to wake up at about 1m range. Normally, it would then
send it's serial number or do an IFF check via RF (see the data
sheet 41099a.pdf at
http://www.microchip.com/10/lit/pline/security/encoders/index.htm)
 but you could use this wake up to turn on your pic and initiate
sending your data over your link. I have played with the device
using the Keeloq evaluation kit and it works well. With a larger
antenna (on the fixed station end particularly) you may get even
more range. The 412 can even tell you when the battery is getting
low by setting one bit in the data it outputs so you may be able to
forget about re-charging on the fly. You will be able to fit the few
components into the space you have available.
>
> The problem with ultrasound is that the transducers are quite thick -
> I have to keep the thickness down to about 3-4 mm.
>
> I have a telemetry transmitter on there already, which is working
> fine, but I need to tell it when to transmit. If it is out of range
> the data will be lost (not to mention wasting power). So it needs to
> know that it is within range. At the moment I simply press a switch,
> but it would be nice to automate this. I don't want to incorporate an
> RF receiver because that would require be a big increase in size and
> power - basically it's not an option. I was wondering about an RFID
> tag, and I still think that's probably the best option. Do you know
> what sort of range you can get with them?
>
> Chris
> --
> Dr. Chris Kirtley MD PhD
> Associate Professor
> HomeCare Technologies for the 21st Century (Whitaker Foundation)
> NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
> Dept. of Biomedical Engineering, Pangborn 105B Catholic University of
> America 620 Michigan Ave NE Washington, DC 20064 Tel. 202-319-6247,
> fax 202-319-4287 Email: kirtley@cua.edu
> http://engineering.cua.edu/biomedical
>
> Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
> Send subscribe/unsubscribe to listproc@info.curtin.edu.au
>



Phil

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