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PGA460: Init threshold issue

Kathy Yeh
Prodigy 20 points
Part Number: PGA460

Hi Sir,

Normally, I can set threshold map to PGA460 successfully, and read sonar distance correctly.

However, I have sensor boards output distance not following the threshold map(TH-A) I designed.

I check DEV_STAT0 register, it returns THR_CRC bit to 0.

Read register 0x5F~0x6E, same as TH-A I set. 

But, when I read distance, it's always wrong.

Wear point is that,

=> If output distance is wrong, not following TH-A, always wrong, until power off. (around 50% probably output wrong distance)

=> If output data is wrong, stop output data. Set other threshold; output is always correct, until power off.

=> If output data is wrong, stop output data. But, set TH-A, again. Output data is still always wrong.

=> If output data is wrong, stop output data. Set other threshold, I tried 3 different threshold setting, all worked normally.

     Then, set TH-A, again. Output is always correct, until power off.

I would like to find the root cause why "returns THR_CRC bit to 0." & "register 0x5F~0x6E show TH-A threshold map", but the output distance did not follow the threshold I set.

 

BR

Kathy

  • 0
    TI__Intellectual 1020 points
    Hi Kathy

    We have got your query. One of the application engineers will get back to you regarding your query in the week of Nov 26, 2018.
  • 0
    TI__Mastermind 27950 points
    Hi Kathy,
    I have responded offline to your TI-FAE contact (Wayne C.) with a full response to this question. Here is an excerpt:

    Based on the "failing" UMR values, the threshold comparitor appears to be triggering very early because the results are mostly sub-3cm.

    a) If the number of objects to detect is increased to 2, does the actual object distance show at object 2? The first object is likely registering the initial burst excitation energy as an object.
    If the second object is the true distance, then you may be able to implement UMR checking at the MCU to ignore any UMR_1 results if <3cm, and check UMR_2 for the actual distance.

    b) Is the THR_CMP_DEGLITCH maximized to 120us? If not, try this setting and rerun your experiment.

    c) When I used the GUI to plot the two preset thresholds, I see that neither is saturating the initial level to 255... What I am suggesting is for saturated threshold masking to ignore any objects within the first 100us (1.7cm) or 200us (3.4cm)... See modified Preset 1 here (notice offset = +7 for level 248+7=255 to enable threshold masking).