[FAQ] Sequence Timings for DLPC347x Light Control Platform
Part Number: DLP4710EVM-LC
we want use the projector for 1D 8bit pattern with a long exposur time.
When using the internal pattern mode in the standart GUI we can set the exposur time to any time we want.
But for exposur times above 18ms we get result in a lower qulity. The displayed picture has bolow 8 bit and the qulity lowers with a higher exposur. For around 50ms we get a 1 bit result.
We measured the Trigger 2 and one LED output with an oscilloscope. The trigger is shown by the yellow line, the LED output by the blue line. When the exposur time is set to 18ms or bellow (picture 1) the LED signal has the same durration an the Trigger 2 Output. When the exposur time is set above 18 ms (picture 2 with 30ms) the LED shuts off after 18ms.
Why is the LED exposur time limited? For Thermal reasons?
Is there a way to extend the exposur time, either with a new firmware or by using another driver triggered by the Trigg 2 output?
We only have experience with the DLP4500. The DLP4500 is capable off very long exposur times.
We just startet using the DLP4710 EVM-LC, due to missing missing user guides we have porblems getting the projector rinnung the way we want it to. Is there an option of directr support, for example via zoom, microsoft teams or other conferenc call systems?
Can you please elaborate on the following?:
"The displayed picture has bolow 8 bit and the qulity lowers with a higher exposur."
What kind of quality degradation are you observing on your system?
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In reply to Philippe Dollo:
Please check this thread which can help you to understand sequence timings support for DLPC347x LC platform. This thread has explained the exposure time supported by the sequences.
In reply to Navneet Singh:
thank you very much for the reference to the [FAQ] Sequence Timings. How ever we are a bit confused, since our observation in the osciloscope doesn't match the specified exposur time. The exposur time for the Seuqence version 0.5.70, for 8 bit Mono is specified with 3464µs - 7600µs in that post. Because of this, we were not shure if this table is correc for the DLPC3479. Especially because in the introduction of the post there is a reference to the software release notes. The DLPC3479 Software Programmer's Guide in the section 3.5.12 Read Validate Exposure Time (9Dh) only mention a minimum exposour time.
Initialy we wanted to use the DLP4710 to reaplace a darker DLP4500 in a setup for scan purposes. The DLP4500 doesn't have a maximum exposour time. This is why we are looking for very long expousur times in the DLP4710.
We get less shades / gradation of the green light (Only mono lighitng wiht green LED in this case).
For short exposoures we get at smooth transition from the bright to the dark area of the picture. The same as the input picture. For longer exposures it epears we are "loosing" bits. For example at 40ms the picture displays a bright and a dark area with only two areas of different shades in between. I appers like a 2 bit picutre, with 4 gradations of brightnes. For even longer exposour we get 1 bit result. The bright area and the brighter shade become one bright are. The dark area and the darker shade also become one dark area.
For shorter exposoure the opposit effect shows. We can alsocreate a picutre with 8 shades of green, like a 3 bit picture. But this is less observable with our eyes. It is hard to recognize the difference between 8 bit, 7 bit and 6 bit pictures.
Can this effect be explained by the way the DMD and Controler turn the data into a picture? Our idea is:
first half of the exposoure time is used to display the first bit
the quater after the first half is used to display the second bit
the eighth after those (the seventh eighth) is used to disply the third bit
the last 256th are used to display the 8th bit.
The DMD expects the whole exposour time and uses it, but the LED olny exposes the first 18ms.
This could be explained by the output trigger and the LED. The trigger shows that some components of the procetor use the set exposur time of 30ms.
But the LED driver can only process exposur times up to 18ms or has a maximum of 18ms for thermal or other reasons.
I hope my explainaition makes sense and is understandable
In reply to Lennart Denecke:
Thanks for informing us, the release notes is not updated correctly and it is still showing the v0.1.10 sequence information. We will update the release note very soon.
Current firmware uses the v0.5.70, the sequence information provided in the FAQ https://e2e.ti.com/support/dlp/f/94/t/778576 is correct information related to exposure time.
Another way to check the supported exposure time : You can use http://www.ti.com/tool/DLPDLC-GUI to check the maximum supported exposure time.
Normal GUI mode -> Light Control -> Internal patterns -> Add pattern set -> Add patterns in set ->pattern set order -> Define pattern set order (add exposure time and pre and post dark time) ->program and load pattern.
If pattern exposure time is supported then GUI will allow you to program the pattern. And you can check whether your exposure time is supported or not.
thank you very much for you explanation.
We already used this option in the GUI
Navneet SinghNormal GUI mode -> Light Control -> Internal patterns -> Add pattern set -> Add patterns in set ->pattern set order -> Define pattern set order (add exposure time and pre and post dark time) ->program and load pattern.
We just want to point out that the GUI only gives an error message if one of the pre and post dark time and the exposour time is too short. If the exposour time is to long the pattern can be loaded to the projector. The exposour time abeve the max expousur time just results in a dark time.
We created the graph for TRIG 2 and LED by using this internal pattern mode.
Could there be an update in the future for longer exposoure times or are they hardware limited?
We are preparing a documentation to explain LC patterns and it's hardware limitations. Once it will be ready we will post it to ti.com.
I will update you once it is available.
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