How to choose a good Bluetooth Module?

17 Feb 2013

Hi everybody!

I'm in a Rocketry Team in which we design and build rockets that actually fly (at least we try to make them fly haha). We usually control the rockets' behavior with an mbed microcontroller, and now we intend to add a Bluetooth module so that we can connect an Android mobile phone to the mbed in order to send simple orders or receive some data at launching.

The problem is: how to choose a correct Bluetooth module with simple Serial communication, which doesn't consume excessive energy, and not too expensive. Moreover, it is intended to work in high atmosphere, where temperature is critically low.

I've considered some modules like: EGBT-045MT, EGBT-046S by Texas Instruments or the RN 42 Bluetooth module which has, indeed, an entry to the mbed Cookbook. However, I don't know much about good Bluetooth specs.

Any suggestions?

Thank you very much!


17 Feb 2013

I think your biggest problem will be range. Normal bluetooth is 10m. Some modules 100m. You probably have line of sight, that is good. You may have a metal fuselage, that is bad. Try to put the module in a tail fin. Another thing may be doppler. I don't know the velocity of your missile but at 2.5GHz you get a considerable doppler shift and I don't know if bluetooth can cope with that. Most cheap modules are for cable replacement and support spp. Usually with AT commands. Power consumption seems to be the least of your problems for an estimated flight time of a few seconds. Alternatively you could consider a prelaunch umbillical and in flight logging to SD which you salvage afterwards. Should work unless you put a warhead onto it.

18 Feb 2013

Doppler won't be an issue. But Bluetooth class 1 lacks the transmitter power he needs.

Better would be to use a Digi International XBee for 902-928MHz if you're in No. America. In the EU/ETSI, 868MHz is a candidate, but there are few products. IEEE 802.15.4 in either 2.4GHz or 868/900MHz with the right high gain antenna on the ground side - is the best you can do unless you get a HAM license and use 150MHz.

Or use the new digital telemetry products from the Radio Controlled model aircraft product world.