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Original question:

BLE Multi hop or daisy chain communication

BQ76PL455A-Q1: Using CC2640 instead of daisy chain communications

Mehmet Ugras CUMA
Prodigy 165 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: CC2640, CC2640R2F

Hi, we are planning to design a wireless BMS with bq76PL455 and CC2640. In the design, instead of using daisy chain communications between bq76PL455, CC2640 bluetooth will be used. Also there will be a master unit that is not seen in the figure. What am I asking is this a good solution? Do you have any experience on this. Kind regards

  • 0
    TI__Genius 17370 points
    Hi Mehmet,

    Thanks for the question! This may be a good solution if your wireless communication is robust and handles each devices data properly but we do not have any experience with this and cannot recommend any best practices for this. However, as long as our devices receive the proper UART commands and have recommended connections elsewhere it may work and I would be interested to see how your solution pans out. Are you planning on handling each device individually or using a scheme similar to our multi-drop configuration as described in our use case scenarios document here: www.ti.com/.../slua785.pdf in section 1.7?

    Best Regards,

    Taylor
  • 0 in reply to Taylor Vogt
    Prodigy 165 points

    I think there is a missunderstanding. As you see from the figure, each bq76PL455 will be directly connected to your TI CC2640R2F which is a bluetooth MCU. We are going to use ARM Cortex M3 core in the CC2640R2F to manage the BMU module. Also there will be another control card which has a TMS570 hercules MCU and CC2640R2F to manage all the BMUs in the system. See the detailed figure below.

  • 0 in reply to Mehmet Ugras CUMA
    TI__Genius 17370 points
    Hi Mehmet,

    Understood, please clarify but I don't see which part where there is a misunderstanding. What my question stems from is the fact that in our typical multi-drop scheme there is an option to have a mcu local to each module/device which is the essence of what you are doing here and device addressing and handling comes into play if you want to broadcast read to all devices at once. I am guessing you plan to handle each 455 device individually and determine which one to talk to by the address defined by the individual cc2640 instead of an address defined by our device? In this case there may be extra delays depending on your number of devices.

    Regards,
    Taylor
  • 0 in reply to Taylor Vogt
    Prodigy 165 points
    Hi Taylor,

    Yes, your guess is right. We are planning to handle each bq455 device individually. But here comes another question at this point. There will be totally 12 BMU units (each BMU reads 16 cell voltages) and 1 BCU unit which will talk together. In the BMS application, BCU will need to gather all the cell voltages to calculate state of the charge as fast as it can. On the e2e forums, I saw that max. simultaneous connections can be made between the master (BCU) to slaves (BMU)s are limited with the RAM. Also your stack is tested upto 8 simultaneous connections. As I am not experienced with bluetooth, is this simultaneous connections limit means that I can only connect only 8 BMUs at once. Than I have to pair other 4 BMUs for communications afterward?

    Could you please advise me a software strategy to read all the cell voltages in a few tens of miliseconds?

    Thank you.
  • 0 in reply to Mehmet Ugras CUMA
    TI__Genius 10785 points
    Hi Mehmet,

    You can connect up to 16 devices.
    I am not sure what limits to 8 devices from previous e2e.

    As example,
    16 cell voltage , 8 cell temp, 1 internal temp
    50 bytes of register reading per device.
    1Mbps is 1uS.
    So you can calculate the time.
    You can use broadcast read so you can read all data with one command.
    You have to add the ADC conversion time then you have complete time for ADC conversion + communication time.

    It can be done in few tens mS.