• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 29 subscribers
  • Views 209 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DLP6500FLQ: Pulsing at bit depths other than 1

Aaron Liao
Prodigy 20 points
Part Number: DLP6500FLQ

I am using a PRO6500 from Wintech Digital which uses the DLP6500. Currently using the TI LightCrafter 6500 & 9000 GUI to control the DMD.

My pulsed laser is operating at 100 Hz with a 10% duty cycle, yet there is significant pulsing when using a bit depth of 8 on the DMD. It also appears at any bit depth above 1, but is most severe and noticeable at 8. I have not yet examined the pulsing behavior with a beam profiler yet, but have observed this behavior with visual and thermal cameras: the pulsing is quite significant and noticeable at around ~10 Hz. I am looking at the exposure time required to display a grayscale images on the DMD and it is significantly lower than the frequency of the laser, so I am confused as to why this pulsing reveals itself even when observing with cameras that operate with frame rates of 25 or 30 fps. 

I am new to using this: any help or point in the right direction is appreciated!

  • 0
    Prodigy 20 points

    Here are a couple of instances where the pulsing behavior is observed with thermal and visual camera capture.

  • 0 in reply to Aaron Liao
    Prodigy 20 points

    Is there any explanation on how the bit depth of the DMD affects the exposure time? 

  • +1 in reply to Aaron Liao
    TI__Mastermind 43125 points

    Aaron,

    TI DLP Technology Digital Micromirror Devices (DMD) create gray scale by using Pulse Width Modulation (PWM). 

    For example if you have an 8-bit gray scale image in your solution (Pattern On-the-Fly, Pre-Stored Pattern, or Video Pattern Mode) then the image will be split into 8 patterns called "bit-planes".  The MSB bit-plane will be shown for 1/2 of the "exposure" time.  The next bit (MSB-1) will be shown for 1/4 of the time.  The MSB-2 for 1/8 of the time and so on until the LSB is shown for 1/256 of the exposure time for 8-bit patterns.

    Therefore what you are seeing is the pattern sequence for your 8-bit image.  I hope this helps.

    You will need to synchronize your camera to capture the correct window to encompass the 8-bit "exposure" (i.e. display time).

    Fizix

  • 0 in reply to Fizix
    Prodigy 20 points

    This makes sense. I looked through some of your other replies to others regarding others attempting to use grayscale patterns, and I will read up on bit planes. Thank you for your help!

  • 0 in reply to Aaron Liao
    TI__Expert 3700 points

    Hi Aaron,

    Glad that Fizix could point you in the right direction! 

    Regards,

    Matt

  • 0 in reply to Matt Soucek
    Prodigy 20 points

    Hi Matt,

    For my application, I would like an even intensity distribution over 2s, and such flashing is not desirable as it causes my substrate to heat and cool rapidly causing a different heat profile than I would like. Is there any way to use this chipset to produce a grayscale image with a more even intensity over a span of time? If bit planes work the way I think they do, then I think the answer to this question is no, since there will have to be gaps between each sequence to reach the desired intensity. 

  • 0 in reply to Aaron Liao
    TI__Mastermind 43125 points

    Aaron,

    I think doing what I suggested by setting the exposure time for the 8-bits to 4046 us and repeating the frame until you reach 2 s should give you a fairly smooth heating distribution.  The LSB is going to present the most difficulty.  Also if you are using a continuous light source, then your lower bits will not have the correct exposure value, since this chipset is expecting to modulate the illumination for the smaller bits.

    What will determine whether your substrate will work at this exposure rate is the of thermal conductivity.  If it cools appreciably in the sub 500 us range then I suspect it will be challenging for your application.

    Fizix