A simple DigiMesh XBee library for Arduino. Because it doesn't really need to be that hard. Oh, and it's not done yet.

• Ability to use any available HardwareSerial or SoftwareSerial instance
• Extremely simple loop() hook, Bee::tick()
• Can send local AT commands
• API frame checksum verification
• Proper explicit escaping (requires AP=2)
• Event-driven, i.e.: Bee::setCallback(myCallback)
• Broadcasting string data very easily, Bee::sendData("Hello world!") (POC, needs to be rewritten)
• Super easy, supposedly bulletproof, fire-and-forget, escaped, raw byte broadcasting: Bee::sendData(myCharArray, sizeof myCharArray)
• Terminate at any time XBee::end()
• Statically initialized, predictable memory usage, no heap fragmentation
• Callback parameter includes a struct with correctly typed pointers to the internal data array instead of providing a copy. Minimizes memory usage.

Comprehensive XBee interface libraries already exist. But for embedded applications, especially Arduino, they're not an option. Their multiple layers of abstraction and internal complexity barely allow them to fit within the entirety of allowable SRAM. It was far easier (and more effective) to start from scratch rather than heavily refactor existing libraries that had no chance of being pushed back upstream.

Bee is written with embedded platforms, specifically Arduino, in mind. It needs to be have small footprint in both compiled size and memory. It also needs to stay out of the way. This means having as little supporting code in your sketch as possible. Bee's tick operation must be quick as to not noticeably impact the average speed of your loop. Dynamic memory allocation should never be utilized as we risk fragmenting the fragile and tiny heap.

The BeeTest sketch compiles for the Mega 2560 in just 4934 bytes (1%) and 691 bytes (8%) of memory. This includes supporting Arduino platform code. On the Uno that's about 26% of memory. Both of these are using the default 255 byte buffer size. By adjusting the buffer (technically the max frame size) you can get these numbers down considerably. If you never expect to receive a packet over 100 bytes in size that's 155 more bytes of memory you have to work with when compared to the default.

Bee has only been compiled/tested on version 1.5.6-r2 of the Arduino IDE and up. The directory structure can be adapted to work on earlier revisions of the IDE. It'll definitely work (has been tested) on an Arduino Uno R3 and Arduino Mega 2560 R3. Should theoretically work on any Arduino. Tested with XBee PRO 900HP 200K (XBP9B-DM) modules on firmware 0x806A with AP=2 (explicit escapes).

Basic Bee implementations can be found in the example sketch directory. A more involved usage of Bee is the Captain project. The two modules use it to communicate with each other (Uno <-XBee-> Mega).

• Refactor or remove the String overload of sendData
• Process other frame types like AT Command Responses.
• Determine if the checksum needs to be escaped
• Provide a way to send frames with custom parameters. e.g.: Changing the destination address of a Transmit Request
• Refactor frame types to their own namespace
• Find a way to change the size of the buffer on compile without having to edit Bee.h
• Optimize tick by removing unnecessary operations. Do we really need to zero the entire data array?

Copyright © 2014 Kevin Mark

Bee is licensed under the GNU LGPLv3, a supplement to the GNU GPLv3. Please see COPYING.md and COPYING.LESSER.md for licensing details.