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Variable LED intensity in different patterns?

James Davis1
Prodigy 160 points
Other Parts Discussed in Thread: DLPC350

On the new Lightcrafter 4500 can I vary LED intensity in different patterns?

a) One possibility would be to set the LED voltage as part of the pattern parameters, is that possible to set on a per pattern basis?

b) I'm looking through shutter glasses at the patterns, so I could also shutter the glasses for half the time while a pattern is on, but if its a 8bit pattern and I shutter away half I'm going to destroy the temporal multiplexing that is producing 8bits unless I'm quite careful. So is there any documentation of the pattern produced when I ask for 8bits? If its a complicated pattern with high rate switching I might be able to shutter away half safely. If its a simple log-ordered pattern then cutting away half might simply cut the low order 7bits.

c) the obvious thing is to change the pattern timings, but I can't do this because I'm up against the minimum pattern times, so can't cut them in half.

  • 0
    TI__Expert 4720 points

    Hi James,

    Please see my responses below in italics.

    a) One possibility would be to set the LED voltage as part of the pattern parameters, is that possible to set on a per pattern basis?

    No, LED settings are not part of the pattern parameters. However, it is possible to adjust LED settings while a pattern sequence is running. Please read section 2.3.7 LED Driver Control of the DLPC350 Programmer's Guide for more details. The guide is available in the Technical Documents section on http://www.ti.com/product/dlpc350

    b) I'm looking through shutter glasses at the patterns, so I could also shutter the glasses for half the time while a pattern is on, but if its a 8bit pattern and I shutter away half I'm going to destroy the temporal multiplexing that is producing 8bits unless I'm quite careful. So is there any documentation of the pattern produced when I ask for 8bits? If its a complicated pattern with high rate switching I might be able to shutter away half safely. If its a simple log-ordered pattern then cutting away half might simply cut the low order 7bits.

    When using Pattern Sequence mode, all video enhancement features are bypassed and a simple log-ordered bit partition system is used. Please see section 2.4 Display Sequences in the DLPC350 Programmer's Guide. If I understand your question, you are correct in saying that shuttering away half of the exposure will cause some bit information to be lost.

    c) the obvious thing is to change the pattern timings, but I can't do this because I'm up against the minimum pattern times, so can't cut them in half.

    True. Probably the easiest option is lowering your bit depth to say 7- or 6-bits so that faster pattern times can be achieved. Please read Table 1. Allowed Pattern Combinations in the DLPC350 datasheet for what the fastest exposure times for different bit depths are available. The datasheet is also available in the Technical Documents section on the DLPC350 TI product page (http://www.ti.com/product/dlpc350).

    Best regards,

    Blair