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Refreshing within a single frame

Melih Okan
Prodigy 75 points
Other Parts Discussed in Thread: DLP4500, DLPC350

Hi,

During a 5s single frame exposure in pattern sequence mode, I send the reflection of DLP4500 to my photodiode and I see this oscillatory refreshing behavior  in every 500us.  Is there a way of getting rid of this behavior?


Thanks, Melih

  • 0
    Prodigy 75 points
    The light i send is a laser beam by the way.
  • 0 in reply to Melih Okan
    TI__Mastermind 30875 points

    Hi Melih,

    The user defined pattern exposure is created out of "base display sequence" and then it is repeated over to 'N' times to match to exposure time. 

    bt X N = PE where bt - base display sequence time, N - Number of time to repeat, PE - Pattern Exposure.

    I think you are using 1-bit pattern sequence,  so for 5-second exposure the DLPC350 is using a ~510us period base display sequence; now every repeated step  (that is restart of base display sequence) causes DMD reset, which produces the oscillating behaviour. This is the way system is architected, so it is not possible avoid the periodic oscillation of 500us.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 75 points

    Thanks for the answer Sanjeev.

    One more question. Is there a way of freezing a frame on DMD? It seems it happens if I click "validate sequence" while the pattern is playing and I don't see spikes of base displays in that case. Is this a reliable way of doing it? Do all mirrors stay in the right position if i do that?

    Best,

    Melih

  • 0 in reply to Melih Okan
    TI__Mastermind 30875 points

    Hello Melih,

    When DMD is in operation, the DMD is continuously refreshing all the time. For reliable operation the DMD must be refreshed. The Validate Sequence is basically aborting and performing the Validation of Pattern LUT and Image LUT settings. During this time DMD is freezing; as a normal usecase to perform Validate Sequence, you must Stop the display of pattern and then issue a validate sequence command.

    Whenever the DMD refresh is stopped the mirror retain last loaded data underneath,  as you are doing. Suppose you are displaying a pattern, then issue a Validate Command, the DMD continue to hold in that position.

    Are you working on a research or some product application let us know, we can discuss offline, we can think of any customization based on the business case which is beneficial to both you and TI. You can send me a friend's request if you want to discuss on this line.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 75 points

    Hi Sanjeev,

    Is there a USB command to change the time of "base display sequences" for pattern exposure mode? We basically want to control the timing of refreshing of the micromirrors. I couldn't see any command regarding to this in the programming guide.


    Regards,

    Melih