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Basic BLE architecture question

Andy Warne
Intellectual 615 points
Other Parts Discussed in Thread: CC2541DK-MINI

I have a project which requires a black box device in a car (which has no user interface) to be controlled by a keyfob.

I would normally use a proprietary RF protocol for this type of project as there is no intelligent host as such, just simple point to point RF communication.

BUT the client also wants to control the same car device using an iPhone. So I am starting out with BLE for this. The question I have is, will it be possible to use the BLE protocol also for the keyfob to car device communication? My impression is that this will not be possible as there is not enough intelligence in either the keyfob or the car unit to act as a master. But before I dive into developing a device with dual BLE and proprietary RF support I just wanted to confirm my thinking is correct.

TIA.

  • 0
    TI__Expert 4060 points

    Hi Andy,

    In a BLE perspective, a master doesn't require more intelligence in the device than a slave - it is mostly a question of who controls the protocol timing. Our BLE stack can be configured as a slave, as a master (supporting simultaneous connections to up to 3 slaves) or as both (you need to switch between the two; you cannot be both a master and a slave at the same time).

    So, I think you should be able to implement what you want with just BLE without adding proprietary RF.

    Best regards,

    Karl

  • 0 in reply to Karl T.
    Intellectual 615 points

    Thanks Karl, 

    Does this means it can be set up to use a simple button-controlled bind? Neither device will have any user display or OS.

    Is there any reference design/project which does anything along these lines?

  • 0 in reply to Andy Warne
    TI__Expert 4060 points

    Yes, a simple button-controlled bind is possible. Not sure about examples of this, maybe one of my colleagues can chime in?

  • 0 in reply to Karl T.
    TI__Guru 57865 points

    Hi,

    I suggest ordering a CC2540DK-MINI (or CC2541DK-MINI targeting RTM end of 2012). There are several project examples that use this functionality. Both KeyfobDemo and SimpleBLEperipheral connects on a button push.

    Best Regards

  • 0 in reply to J Lindh
    Intellectual 615 points

    Thanks. I have this kit. I have been using it and have the examples working but none of them connect on a button push at both ends. All the projects require a host at one end, either the PC with the dongle, running BTool, or the iPhone. 

    Yes the button on the slave makes the device discoverable but the process of searching for the device and connecting to the correct device seems to require an OS and a display on the master unless I am mistaken.

  • 0 in reply to Andy Warne
    TI__Guru 57865 points

    Hi Andy, 

    Typically (as it seems in you application as well) the part located in the car will be powered by a larger power source than a simple battery, am I correct? In that case, you can have it scanning/advertising (depending on functionality) all the time as I assume the natural dissipation in a car battery is lower than uAs of active BLE device. Just thinking out loud here though. 

    If the device in car is running on small battery, I suggest it's designed as a peripheral device simply advertising with long intervals (1s?) and by that keeping the power consumption relatively low. This depends of course on how  fast you want the connection to be. 

    Could you elaborate a bit on the use case.

    Best Regards

  • 0 in reply to J Lindh
    Intellectual 615 points

    Yes there would be no problem with power consumption in the car unit.

    Now I know I am not going down a blind alley I will do the research and find out how it all works. 

    Thanks