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DMD contrast issue

Adam Cohen2
Prodigy 20 points
Other Parts Discussed in Thread: DLPC350

Hi,

I am trying to use the LightCrafter 4500 with external LEDs.

As such I have unplugged the LEDs and reconnected the DMD to the board without the lightengine (as in the image below)

.

I then connected the board to a 12 V supply neglecting to connect the J30 jumper. After about 30 seconds of operation (and a concerning vibrating sound) a thin band appeared on the DMD. It can be seen the figure above and upon re-projecting the logo image it can be seen in the image below.

Inside this band (neglecting inversion) I have good contrast but outside I have poor contrast. If I do a forced swap from video mode to the pattern sequence in the GUI the image freezes to a high contrast image. So high contrast is achievable (but through a glitch).

Question 1: If I run a sequence with a long exposure time (as bellow) would I expect with a normal operating unit a high contrast image on the DMD? (the micro-mirrors being fixed to either + or - 12 degrees?)

Question 2: What is causing this contrast problem and how would one go about fixing it (software or hardware)? If the problem is hardware, where would it be more probably localized? the DMD, the DLPC350 or some other place on the board?

Thank you for any help,

Bogdan

PS: The firmware is updated and the green LEDs on the board are blinking.

  • 0
    TI__Expert 4720 points

    Hello Bogdan,

    I suspect that the DMD and or flex cable is not properly seated creating a disconnect for one of the DMD's signals which is causing that band your describing.

    When the DMD is operating the mirrors periodically update the ensure maximum lifetime of the mirror. Also in your GUI settings you have the pattern exposure time longer that the internal trigger which is incorreect. The internal trigger needs to be at least 250us longer or the same as the exposure time. I suspect that your contrast problem is caused by this invalid setting.

    Please correct the timing settings and let me know if your contrast improves.

    Best regards,

    Blair

  • 0 in reply to Blair Conner
    Prodigy 10 points

    Hi Blair,

    I have a very similar issue after disconnecting the light engine. There are two bands appearing in all the modes (pattern&video and boot image; see images).

    Is there any experience where this could come from? I also heard the vibrating noise. I reconnected the DMD and flex cables several times and the band always appears in the same position. Is this a problem with the controller or may it be a damage to the DMD itself? 

    Best regards

    Florent

  • 0
    Prodigy 50 points
    Hi,

    I know this is years later to your original posting however I am working with a TI DLP NIRscan EVM which uses a very similar if not the same DMD as yours was and it has suddenly started having the same issue you had Bogdan. It appears to have the contrast band issue in an identical spot to where yours was (based off the image shown on startup).

    Did you ever find a resolution to the problem?

    Thanks,
    Ben