On Sat, 26 Oct 2013 13:53:51 +0100, Bill Hill rtufty@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.