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MSP-EXP430FR5994: Reading Two Tri-Axial Accelerometers Simultaneously

Larry Hawker
Intellectual 460 points
Part Number: MSP-EXP430FR5994

Hi,

 I am developing a device that uses two tri-axial accelerometers. I need to measure the six signals simultaneously and react in “real-time” (i.e., with minimal delay). I have tried using analog accelerometers connected to the MSP-EXP430FR5994, but switching analog channels requires a long settling time. I have tried digital accelerometers where I can read three signals (x-y-z) at once from one accelerometer, but there is an unacceptable delay when I switch to the second accelerometer (by then my device has changed behaviour/position). I don’t think a simple multiplexer (MUX) will help since I would still need to switch between the six channels.

 Can anyone suggest the proper way to do this and the device to use? I don’t know if I need something with a sample and hold feature or what.

 Thanks,

 Larry

  • 0
    Guru 35620 points

    I would use two interrupt based SPI buses so that you can read both at the same time. DMA would even be awesomer.

  • 0
    TI__Mastermind 32920 points

    Hi,

    Why you need to switch between these two accelerometers? I think you can just read six signals  in a "Repeat-sequence-of-channels" mode. You can also use DMA to transmit data, if the CPU transmittion speed is much slower than you need.

    Besides, change the frequency of MCLK, ADC clock, ADC sample rate to max, it will also help to reduce time.

    If all this is not help, you need to optimize your code.MSP430 Optimizing C Compiler User Guide.pdf

    Eason

  • 0 in reply to Eason Zhou
    Intellectual 460 points

    Thanks for the suggestions. I have not used DMA before so I will have to read up on it. Same goes for the "Repeat-sequence-of-channels". Since receiving these replies I have seen a number of entries on the forum for “Repeat-sequence-of-channels" so I guess that's the place to start. Hopefully I can find some easy to understand examples.

    FYI, for the digital side I am using two STMicroelectronics STEVAL-MKI175VI evaluation boards with LIS2DE12 accelerometers. On the analog side I am using two Analog Devices ADXL326 on Adafruit boards. (I assume what I am using on the analog side is irrelevant since it is the MSP430 that does all the work reading the voltage levels.)

  • 0 in reply to Larry Hawker
    TI__Mastermind 32920 points
    Hi,
    OK, I will close this thread.
    Be careful that when you use DMA, you can't use CPU at the same time. It may be different will other MCUs.
    Eason

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