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MSP430FR6043: Sampling frequency limitations and ToF outputs

Brent Weight
Prodigy 150 points
Part Number: MSP430FR6043

Our ToF is in a very specific window. We would like to increase our sampling frequency so we can get a cleaner capture of the peaks but the TI Design Center only allows us to select 1000 and 2000 kHz signal sampling frequency?  Yet the table that pops up when you hover over the Signal Sampling Frequency box suggests that there are several more options available. We are running the 80 MHz USSXT.

Why are the other options not available? 

We manually edited the header file and tested 4000 kHz with oversampling at 20.  We were able to get the ADC capture, with much cleaner data, but the Delta ToF and Absolute ToF values all came back as 0s.  Is there now way to get faster sampling and still use the TI algorithms?

Any help is appreciated.

  • 0
    TI__Genius 12980 points

    Hi Brent,

    Reading over your values, it appears to me that you've adjusted this correctly. You can find some more information about this in this thread and the threads that it links. Basically, the signal sampling frequency needs to be equal to the PLL frequency divided by the oversampling rate. The default PLL frequency is 80MHz, have you left this value alone?

    My impression after reading the post is that the values you set should be ok and you should be able to get valid time of flight calculations. When you enter the default values in the header file, are you seeing the TOF values reappear?

  • 0 in reply to Dylan OBrien
    Prodigy 150 points

    Yes when we manually edited the header file we left the PPL at 80 MHz.  We increased sampling frequency from 2000 kHz to 4000 kHz and reduced oversampling from 40 to 20.  We could get ADC capture data that appeared to be sampled at twice the rate, but the T of F parameters (UPS, DNS and delta) were returned as zeros.

    Yes when we return to default values, we get T of F values reappear.

    Is there some reason why the Ultrasonic Sensing Design Center application, only allows us to select 1000 kHz or 2000 kHz as the sampling frequency?  The oversampling is automatically calculated in the application, and uneditable.

  • +1 in reply to Brent Weight
    Expert 1950 points

    The higher frequencies are for water meters.

    The gas algorithm only allows a maximum 2 MHz sampling frequency; there are probably hard checks in the algorithm's "black box" for sampling frequency and your higher sampling rate is causing the algorithm to throw an error code. The algorithms don't work any better with higher sampling rates as they assume only a handful of samples per waveform period anyways.

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