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Original question:

DLP651NE: dithering and flickering question

DLP651NE: follow up on flickering and electronic signal not corresponds to true flickering

Babak Imangholi
Prodigy 40 points
Part Number: DLP651NE

Tool/software:

Hi Gary,

you closed our case... I have a follow-up question on "DLP651NE: dithering and flickering question", linked to this question. 

we continued and did more testing by placing a fast Si detector under the DMD projector. and got following result: 

the yellow signal is the signal LED_EN_RED from J97 Pin 4 and the red signal is the signal from Si detector indicating when dithering or flickering occurs. we need to know when flickering occurs to turn off the LED.

however, use of signal LED_EN_RED from J97 Pin 4 is is hard to use for this because the falling edge does not always correspond to this time period. In other words, only every other falling edge corresponds to the dither.


we need to know exactly when flickering or dithering occurs. can you please advise what pin to use or what to do to get corresponding 60Hz flickering or dithering. I am talking about dithering/flickering (whatever you call it correctly) where you mentioned following in linked thread==>
"... all of the mirrors to move fully (+/- 12 degrees) at least once per 60Hz frame time, even if the video data is full white or full black for a long period of time.  The illuminators (RGB illuminator enables / strobes) are disabled / off during this time, so this is not visible on the screen in a video application."

we can see it via optical detector but using electronic signal LED_EN_RED from J97 Pin 4 is is hard to use for this. It is because the falling edge does not always correspond to this time period. In other words, only every other falling edge corresponds to the dither.


thanks for URGENT response.
thanks
Babak. 

  • 0
    TI__Expert 6245 points

    Hello Babak,

    It is likely the system automatically closed the case as it has been opened for a month without a response. We try to keep the amount of threads lower as this helps customers with questions searching for help with their possible questions.

    If you are planning to turn off the LEDs during dithering you will have worse performance than is intended. The dithering/flickering is a spatial and temporal solution from TI (our IP) that makes the image look better to the human eye.

    Please note again Gary's last comments:

    "I believe I have addressed the initial "dithering and flickering" question as best we can for this product.  At this point, we are well beyond the scope of what is supported for the 7540; it is a video display product for video display applications.  We really cannot document every possible case of the mirrors moving, not moving wiggling, etc..  The 7540 does not offer that level of control of the DMD to the end user."

    Additionally:

    "I do not believe it has the ability to disable dithering or the pwm seqencer; those are fundamental to normal (and safe) operation."

    Dithering/flickering is built into the controller because of the application. If you are trying to go around the solution, this needs to be applied with a different controller for another application.

    Best,

    Aaron

  • 0 in reply to Aaron Black
    Prodigy 40 points

    Hi Aaron.
    Thank you for your response. but kindly you are not answering my question.  Please let me ask it differently=>
    I am looking at signal LED_EN_RED from J97 Pin 4 . Gary told me this signal represent the flickering of DMD. but it does not , please see below pictue==> 

    We want to use LED_EN_RED from J97 Pin 4 and we will build our circuit to turn on or off LED. but we need to know when DMD is flickering. We are not asking or we do not want DMD DLP651NE to turn on or off the DMD. We want DMD board tell us, somehow,  it is happening. a signal informing us of happening/occurrence of flickering event.

    Gary said  Electronic signal  from LED_EN_RED from J97 Pin 4 of DLP651NE board represent the DMD flickering. But this signal is occurring twice the frequency of dithering/flickering of DMD. We can not use the rise of fall edge to detect when DMD is dithering or flickering.  please advise if you know a way to solve this issue. any other pins on DMD board that inform us, send an output that is indication of flickering/dithering occurrence? 

    thanks so much 

    Babak

  • 0 in reply to Babak Imangholi
    TI__Intellectual 2570 points

    Babak,

    The project is for an RGB LED system.  There illumination is controlled by 3 enables (R, G, and B).  If you want to know when the controller is not intending to display something, you need to look at all three LED enables.

    Regards,
    Gary