LC4500 gapless pattern display

Jakob,

We are aware of the potential for improvement in GUI 1.1.0. A new GUI is to be released soon.

For questions 1&2) Each pattern in the sequence has a trigger type: external positive, external negative, internal, or no trigger. When using the vsync as a trigger, the first pattern in a frame is set to 'external positive', and the next patterns are 'no trigger.'

1) The internal trigger should be set equal to the vsync period. If the timing for all of the patterns in a frame is less than the vsync/trigger period, you could see a dark image/flicker. If the timing for all of the patterns is greater than the vsync period, the GUI should warn you of an error.

2) Do you want the the Vsync to only start the pattern sequence and then be ignored? If so, this may not be possible. As the pattern sequence repeats, the first pattern, which is defined as 'external positive', will wait for a vsync. TRIG_IN_2 is a start/stop trigger that could be of use.

3) Saving solutions will be available in the next GUI release.

4) Right click on your pattern and uncheck "Clear DMD after exposure". Or, rebuild the pattern sequence, but do not clear the DMD after exposure (the box next to Add Pattern to Sequence).

Regards,
Stuti

Hello Stuti,

thank you for the advice. It seems upon further investigation, that the sporadic black frames are caused by a slightly delayed vsync from my computer. The LC then gets the new frame too late and shows a black frame for about one exposure period.

In order to fix it, I have to reduce the exposure time by quite a bit ~200usec. This in turn leads to a notably flimmer at all times. That works OK when my camera is triggered and set to the same exposure time, however it does not work well with a software triggered camera.

By unchecking "Clear DMD after exposure", the sequence check complaints that a "black vector" is missing, so this is, unfortunately, not an option.

Best,

Jakob

Hello Jakob,

There are two modes for exposure times/trigger periods. The first one is that you need a 230us delay between the two to allow time to clear the DMD. 

However, if you are not clearing the DMD, then you can make the exposure time and trigger period equal. 

On that same note, the "black vector missing" error is a warning (not an error) that the DMD is not being cleared. If your pattern sequence is running, you can choose to ignore this warning. 

In summary, I suggest you try unchecking the "Clear DMD" box and removing the difference between the exposure time and trigger period. If you still see a flicker, then set your trigger period slightly lower than your vsync period. Hopefully this setup will remove the flicker.

Best regards,

Stuti

Hi,

I came across this post with the same issue as Jakob and I can't resolve it yet:

I also would like to project a gap-less pattern from a video source. I have the dlp4500 hooked up as a second monitor and I am taking high speed recordings of the projection with 2ms exposure time of the camera.
The video source is being projected OK but depending on the timing settings in the dlp-gui, I get more or less noticeable flicker that I can't fully eliminate.

Is there a straight forward way to determine the appropriate settings for dlp timing and exposure to achieve a truly gap-less pattern projection? I'll admit I don't really understand the dlp technology, so please let me know if I am missing something fundamental or of this isn't even possible.

thanks,
Johannes

Hi Johannes,

I am not sure this applies to your case, but remember that DLP projectors basically project binary patterns (at kHz rates). Gray values are generated by modulation. For truthful gray value reproduction (without flicker) in your camera, the camera exposure needs to be a multiple of the pattern exposure time. 

/Jakob