27 Oct
2013
27 Oct
'13
12:53 a.m.
On Sat, 26 Oct 2013 13:53:51 +0100, Bill Hill <rtufty(a)gmail.com>
wrote:
Hi, the Xbees are XB24-BCIT-004, which are Series 2,
chip antenna, radio data rate 250Kbps.
The path length is about 2'6"
I'd suspected that it was something with packet collision/overlap - I'll have a
poke and see
if there's anything to change with RTT. It's not critical, I got the Xbees for a
greenhouse
temperature sensor and just "repurposed" them to remind myself how to do serial
comms.
I haven't used the XBIB; just cheapie USB boards.
The platform is interesting and the development environment is a bit
of a challenge and messes me up a bit since I am used to Visual Studio
and CodeWarrior's IDE is close enough to it to make you comfortable
but far enough from it to make it difficult. Needs more coffee. :)
I'm still learning my way around and it took me a while to learn to
use X-CTU to configure the modems. I'm playing around with their AT
command set too.
Something to be aware of: they don't set any flow control by default
and I've been experimenting with them with a terminal application and
Digi's X-CTU app. The buffering seems to be unreliable and just
streaming chars to the modem, they will fail to transmit a char or
two, just from the keyboard at high repetition rates.
Copy-paste loses hundreds of chars. The XBP9B's I am using have 256
byte frame sizes and you can reliably send up to about 1024 bytes in a
single frame... once. After that it only forwards 256 bytes per
transmission and the only way they will recover is if you send a
smaller frame of less than 256 bytes. I can get them to send 260 byte
frames at just about any repetition rate at 115200kbps and they don't
fail to transport them but there seems to be something near 512 to
1000 bytes where they start to lose it. Make sure your SLIP driver
can't blow past the modem's buffers on a single frame and has
initialized proper flow control.
I've got both the RasPi and a BeagleBone Black,
though I've used the Pi more. (I've got 2 of model a
sitting waiting for me to solder up the TNCpi kits, which is what prompted me to join this
group.)
The RasPi is (slightly) cheaper and a lot better at multimedia - XBMC and the like. The
BBblack seems
to have more resilient, and just more, GPIO. The BBblack has a much nicer hard real time
system, the
Programmable Reatime Units (PRU). The LinuxCNC guys love it. The RasPi seems to have a
much larger
user base, and lots more accessories. For example, the Cooking Hacks "Raspberry Pi to
Arduino shields
connection bridge" which has Xbee socket connecting straight to the RasPi; or the
TNCpi. (I'd love a
TNCbeagle!)
The BBblack has support for "USB gadget" api, so you can program it to act as,
for example, a
USB keyboard, mouse or network dongle.
For talking to an Xbee I'd go for a RasPi, but pretty much for the feeling that the
BBblack was too
good, and the RasPi, model b, has 2 USB sockets.
The LinuxCNC reference has me intrigued also. I come from a CNC
background and have dealt with RTOS all my career. I think I will
probably end up buying two of each. :)
I have specific requirement to fulfill that's not Ham related where
I'd like to be able to plug Ethernet into the devices and transport
CNC part programs from a host to a machine wirelessly without having
to deal with driver installations on the CNC. An XBee on a BBblack
might be what I am looking for.