Communications

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So far, we've converged on the use of Zigbee (pro, probably) modules. These operate at 2.4 GHz and provide a serial link among participants in a Personal Area Network.

They're described here:


Since the playa, we are transmitting on Zigbee Channel 0xF with a PAN ID of 0xFADE Jtfoote 15:37, 23 October 2007 (MST)

To Program XBee module, look at p. 26 of Zigbee manual.

Out of the box it is set up at 9600 baud, so set your terminal program to that.

First thing you want to do is to change the baud rate:

To set baud rate to 38.4 kB:

 +++
 ATBD5
 ATWR
 

AT commands: on bootup, send this over serial at the right baud rate (38.4 kB) to set channel and pan ID:

 +++
 ATCH 0x0F
 ATID 0xFADE
 ATWR
 ATCN

Don't forget to WRite it to flash!

As a sanity check, you can read back parameters (baud rate, channel, etc.) by issuing a parameter-less command.

eg. to check that it got the ID ok,

type

ATID

to which it will respond

FADE

It takes it a little while to boot (I think) so be patient with the "+++"s. Give it a few seconds to come back with "OK." Also I think it times out of command mode if you don't give it a commands fairly quickly.

Minutes from BMORG playatech meeting

On Thursday, April 12, 2007 there was a meeting to coordinate use of the RF spectrum at Burning Man 2007. The primary focus of this meeting was 802.11 and other network infrastructure, but input from artists using the RF spectrum was solicited so that coordination is possible.

Attending from Swarm were Jonathan Foote and Tad Rollow. We informed the group of our interest in using Zigbee, a FHSS system at 2.4 GHz, with mothership antenna height at approximately 10 feet and node antenna height at approximately 3 feet. The consensus was that Zigbee co-operates with 802.11 just fine, and that we are at relatively low risk of interfering with playanet and other 802.11 users.

We will want to coordinate with other Zigbee users (L3K, for instance) so that we aren't using the same PAN ID, and we've already discussed at our meetings (Pete and Jon, for instance) that we can lock our network to the specific 64 bit IDs for the nodes we know we own.

Generally, the BM frequency coordinators use appropriate calculations based on output power and antenna height to determine coordination. We've informed them that the Zigbee Pro modules operate at 60 mW power into 1/4 wave or better antennas.

It will be informative to test this stuff, mostly with nearby 802.11 equipment, so we can determine the susceptibility of each system to the other. Current plans are to test this locally ourselves, and to test on the playa during Geek Week, when they'll have a full infrastructure in palce to do load testing of their networks, and we should bring a full complement of nodes under high traffic load to participate in this test.

The remainder of the meeting was focused on IP address and routing allocations for network users. We have not requested any Intertube access for our project.