Re: RFID for HA

[ddl@danlan.*com (Dan Lanciani)]

In article <e0ves8$53g$1@xxxxxxxxxxxxxxxxx>, lee@xxxxxxxxxxxxxxxxxxxxx (E. Lee Dickinson) writes:

| This strikes me as a terrific idea. The whole reason I'm interested in RFID
| is to know if my cars are in the driveway. If both are gone, temperature
| adjusts, doors lock, roomba vacuums... etc.
|
| So I don't even need a small battery powered chip. It could be bigger. A MCU
| with an off-the-shelf USB access point. Or one of the smaller chip
| solutions, but not wallet-sized.
|
| Anyone have any ideas?

I've gone through several generations of this.  The first uses a moderate
sized old laptop (Toshiba T1910) with a PCMCIA 802.11b card in each car.
The second used a smaller computer.  The third uses a modified Aironet
BSE in a WGB-like mode.  For the first two generations I run my own tcp/ip
stack tweaked to reset the ICMP timestamp response value to 0 on startup.
The third generation provides an uptime value via SNMP.  First and third
generation are currently in use.

I power the 802.11 device (computer or BSE) only when the engine is running.
A daemon running on my automation computer periodically queries each car for
its uptime and generates events when a car appears or disappears.  It infers
from the uptime whether the car is starting up or coming into range (for
appearances) or shutting down or going out of range (for disappearances).
The inference based on uptime was intended to be a temporary hack (to be
replaced with either explicit status messages or signal strength tracking)
but it has worked so well that I've been reluctant to introduce more
complexity.

It is critical for the car-based device to boot up and start responding
to queries before the car gets out of range when starting/leaving.  Even
many DOS-based laptops waste a lot of time in the POST, making them useless.
The Aironet BSE platform (same hardware as WGB) runs the code from flash so
it doesn't waste any time decompressing code and such.  None of the other
Aironet platforms are suitable.  I haven't investigated other brands, mainly
because the Aironet platforms use the Aironet PCMCIA cards and they have
great range...

				Dan Lanciani
				ddl@danlan.*com