Bluetooth Guru's?? Advice on Bluetooth version with Android

[ONETEN]

Hi Guys,

Not sure how well a question like this will be fielded on here, as its not so common!

I am working on a project (still) which I had intially intended to read data off a CAN bus (1mbit) and display on an LCD. Wisdom shone down upon me and I realized how much more effective it would be to instead use a Bluetooth module and communicate with an Android device and use that to display my data. I am planning to use the Bluetooth in SPP mode and just shoot the data via UART from a PIC32 MCU.

After abusing google & reading many data sheets, I am tossing up between going for a Bluetooth module version 2.1 + EDR (3mbit, to give me the overhead above CAN speeds) or Bluetooth 4.1 (24mbit).
Off the bat, BT 4.1 looks like the logical choice (being newer tech), but I want my device to be able to work with as wide a range of Android devices as possible. I don't need massively high speeds, and it is unlikely that even though the CAN bus will operate at 1mbit speeds, the FIFO buffers will ever have much in them.

The issue is older hardware, not so much software. I am not sure how backwards compatible BT 4.1 is with BT 3.0, 2.1 & 2.0 hardware based devices? Does anyone have any experiences with this? I can see that BT 4.1 is backwards compatible with 3.0, but not so clear whether this also applies to 2.1 and 2.0.

I am also concerned if I go with an older BT 2.1 + EDR device ( Like the Microchip RN41) that it might be a just a pointless exercise using aging tech and I wont be gaining any compatibility or ease advantage.

I think BT 2.1 + EDR would be most ideal (as it appears to still be by far the most popular) but I am not experienced with this sort of stuff, so if anyone has an opinion they can share I would love to hear it.

Cheers,
Hayden

[Maxlor]

I've used the RN42 module with Android before, and it's reasonably easy to get it going with SPP to an Android device. You'll never get 3Mbps over that. With a different profile (not serial), and under ideal conditions, maybe.

But if this is for display purposes, are you sure you really need such a high data rate? If you reduce the data size on the PIC and send just the final values that actually get displayed, you'll probably get by with a handful  of bytes per second.

[ONETEN]

Thanks Maxlor.

Yes the RN42 is what I have my eye on, Microchip sell a version on a small breakout board with USB so you can send commands direct from a PC.

I will probably grab one of those for testing for now. I certainly dont need near 3mbps but I do want to ensure It can keep up with the CAN data coming in to the MCU. And yes you are correct about the display purposes, the human & eye and brain can only go so fast but reducing the data size on the PIC has some complications which I wont expand on here - I will be typing for days.
I am hoping to do the higher level translation of the CAN data directly on the Android as its obviously going to be easier and more efficient on a higher level device.

If speed is going to be the main defining factor in a choice between BT 2.1 and BT 4 then I will probably just stick with 2.1. Such a large pool to choose from too.

Thanks for your input! Much appreciated.

[Karel]

Today I did some tests with the WT12 from Bluegiga. I ordered a couple with iWRAP 5.0 firmware pre-installed.
SPP is default enabled. I did some tests at 18KByte/sec. and most of the day I reach a max distance of 8~10 mtrs.
Sometimes I have to lower the datarate because there's too much traffic/noise in the 2.4GHz band.
So, in the end, there is the maximum possible throughput but there is no minimum guaranteed throughput.
I think it's safe to say that an average speed of 18KByte/sec. over a distance of 3 mtr in SPP mode is possible 95% of the time.