Hello!
I’m planning my first Arduino project and am struggling to select the best hardware for supporting Bluetooth. The “Arduino BT” has apparently been “retired” (per Arduino’s website). The Arduino 101 apparently has powerful Bluetooth support, but it seems to be the only Arduino that uses an Intel “x86 (Quark) processor and a 32-bit ARC architecture core” instead of an “ATmega” processor from Microchip Technology. Besides wondering if all of the common Arduino software works on it, the Arduino website says that the 101 is “out of stock.” (I have no idea if this is due to really high demand or really low demand for the 101.) Finally, I see that there are a number of “HC-05” add-in modules available (although not directly from Arduino), but it seems like these only support Bluetooth 2.0 and I figured I’d use newer Bluetooth if I could. (The HC-05 boards I found also require a resistor divider to keep from (possibly) burning out the Rx pin of the HC-05 chip.) And, of course, with multiple HC-05 boards available, I don’t know which one is best to start with.
Although none of these parts are that expensive, I’d hate to waste time by not starting with the best hardware for a Bluetooth project. Thank you for any advice regarding the best, most up-to-date Bluetooth hardware available for the Arduino!
Best is a relative term and depends on what your Bluetooth project is. If it involves iPhone, beacons, RSSI, or working over distances greater than 10m, then newer bluetooth is the only way to go. For regular SPP data transmission, the HC-05 is the better choice. The reason why HC-05 is not available from Arduino is probably because it is not an Arduino product, but confining yourself to only to Arduino products is probably an as temporary an affliction as it is a silly one.
One HC-05 board is much the same as another - just get the cheapest, about $3-50. It is good practice to use the voltage divider on 5v Arduinos.
You might find the following HC-0x background notes useful.
http://homepages.ihug.com.au/~npyner/Arduino/GUIDE_2BT.pdf
http://homepages.ihug.com.au/~npyner/Arduino/BT_2_WAY.ino
I think BLE is more trouble than its worth, but I'm just interested in data streams. The best information I know of is here
http://www.martyncurrey.com/hm-10-bluetooth-4ble-modules/
Thanks much, Nick.
My plan was to talk from Android via Bluetooth to TWO separate Arduinos. Less than 10M will be fine (presuming that 10M spec I've seen in the HC-05 documentation is not super-duper best case). While this is NOT going to be high volume data, neither do I have a need for BLE for this (my first Arduino or Bluetooth project). That said, you never know what other projects the future has in store! 
I do note that you've sent me pointers to three resources. I will gratefully read them all.
Do you happen to know if any of the HC-05 boards are plug in "shields" that already have the resistor divider built-in? (I'm an EE and handy with a soldering iron, but I don't want to have to dink with a production board if I don't have to.)
Thank you very much!
somethingfishy:
My plan was to talk from Android via Bluetooth to TWO separate Arduinos.
This can be done but I'm not sure that it is something you would want to write home to your mother about. An NRF24 network is made with this in mind and has about the same unit price and performance. You can even use a high power version in the base and get considerably greater range. If you use bluetooth, the base station must be a master and configurable from within the programme.
Do you happen to know if any of the HC-05 boards are plug in "shields" that already have the resistor divider built-in?
No, but I imagine they do. Note that the Itead shield is not an HC-05, it is an HC-06 and therefore slave only.