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CCS/CC2650STK: Accelerometer maximum output data rate

AL_Spain
Intellectual 340 points

Part Number: CC2650STK
Other Parts Discussed in Thread: CC2650, , BLE-STACK

Tool/software: Code Composer Studio

Hi everyone. I hope you can clarify me this doubt.

I want to know how fast I can acquire accelerometer data to be sent through BLE (only acelerometer data, not gyroscope or magnetometer).

I have the CC2650 STK, and I have been looking for any information about it but I do not have it clear yet.

I know that the CC2650 is connected with the motion tracking device (MPU-9250) via SPI. According to its datasheet, the MPU-9250 has a maximum output data rate of 4 Khz (so I suppose that it would be possible to acquire data at this frequency), and the accelerometer data size is 16 bits per axis (3 axis) . According to the CC2650 datasheet, the SPI interface supports up to 4 Mhz (so it could be phisically feasible to acquire accelerometer data at 4Khz and have it ready to send in the CC2650)

Another restricting features that we need to take into account is the BLE connection period and the packet size. I have seen in anoher forum thread  that the minimum BLE connection period is 7,5 ms, but it would be possible to increase the default MTU size to send more data in a connection event. My doubt about it: is it necessary to stablish a connection every time I send packets over BLE? Is it true that the minimum BLE connection period is 7,5 ms? What is the maximum MTU size?

What I am looking for is the maximum accelerometer data rate that allow us to package this info and send it via BLE using the CC2650STK. 

Thank you very much for your support. Any help will be welcome.

Thanks again.

 

  • 0
    TI__Guru** 105180 points
    Hello,

    TI has not tested other configurations of the MPU-9250 other than the SensorTag sample application, so I can't comment on faster reporting of g-sensor data. You can see a description of the movement service in the SensorTag User's Guide on the TI BLE wiki, including the relevant files. Note that the sensor is connected to the CC2650 over I2C, not SPI, on the SensorTag.

    The maximum ATT_MTU size is 251 bytes. You can find more details in the SW Developer's Guide (SWRU393) which is included with BLE-Stack SDK v2.2.1. See "5.5.2 Maximum Transmission Unit (MTU)".

    Best wishes