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LED illumination strength in the 3.3V ext trigger mode

wei hao chang
Prodigy 130 points
Other Parts Discussed in Thread: DLPC200

Hi,

I am using the lightcommander in 3.3V ext trigger mode to project images. 

I am using setting of 205 Hz and 4500 microsecond illumination time; I uploaded the set images and compile using 45, 40, 35, 30, 20, 10, 5,% (compiled each time) illumination strength for all three LED (all enable) to test out the changes in projected intensity values. Though, when operating in the external trigger mode, the intensities that I captured using a scientific camera shows not much of difference when I adjust the LED driver strength (%).

Therefore, I am wondering if there is a delay or a charging time for the LED to reach the specified illumination strength that apparently cannot be done in the external trigger mode with a set illumination time.

Wayne

  • 0
    TI__Mastermind 30875 points

    Hi Wayne,

    The behavior what you are observing is expected.

    Reason:

    The LED driver used in the LightCommander(TM) has dedicated SPI bus interface on whic DLPC200 controller sends the current strength information. The LED Driver accepts strength setting only when additional hardware signal (LED_SUBFRAME) input to it is active. This signal is generated by the DLPC200.

    What happens is when the LightCommander(TM) is running in 'AUTO TRIG'  mode, this signal is continuously active and LED driver takes strength setting immediately. Now in the 'external hardware trigger' mode this signal is active only when the external trigger active. So, when you try to update strength from GUI there is no LED_SUFRAME signal active in the system beause you are not sending the trigger pulse. This will cause LED driver to not accept the strength information setting.

    This is the reason why are seeing same reading on scientific camera.

    For current strength update AUTO TRIG mode is suggested. It is possible to update the strength setting in hardware trigger mode if you are running the hardware trigger pulse continuously, this will be like 'AUTO TRIG' setup.

    Regards,
    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 130 points

    Hello Sanjeev,

    Thank you for your help. Though, can you expand on the the last part of your answer? In my case for example, if I would of want to lower my intensity from 45% to 5% and see the effect in hardware trigger, I would have to update the setting and run it in auto trigger mode for the LED driver to update, once the LED is updated, I can use hardware trigger and will see the 5% effect? If I switch the trigger mode from auto to hardware, would the LED driver return to default value?

    Also, for the last part of your suggestion, where you said it is possible to update the strength setting in hardware trigger mode playing continuously, how long should the pulse width and period be? I conducted an experiment using "continuous" (a train) of 25 hard trigger signal playing 25 images with width of 4500 microsecond, and a cycle of 104500 microsecond, and according to your answer, when I vary the power (45%, 40, 35, 30, 20 ,10, 5) the power should be updated throughout the continuous signal, and there should be a difference between the 7 sets of images, though the intensity values between the 7 sets does not seem to change.

    Thanks,

    Wayne

  • 0 in reply to wei hao chang
    TI__Mastermind 30875 points

    Hello Wayne,

    The method you are following to change intensity is correct. LED driver will not return to default value until you power cycle or press 'Hardware' or 'Software' reset button on the kit. So your method to change intensity will work.

    On the second part, if i understand correctly, your configuration is following - there are 25 images to be displayed in 'external h/w trigger' mode, the display time or exposure time of each image is 4500uSec and display rate is at 104500uSec = ~10Hz.  This means pattern displayed for 4500uSec at 10 fps. Let me know if my understanding is incorrect.

    To update one LED current LED driver needs two triggers, so if you are setting Red then Green then Blue, the overall setting effect will be seen after 6 trigger pulses i.e., on issuing 7th trigger pulse, the intensity change is what you are looking for. Note as we are updating one current at a time, the intensity reduces step by step, for example, 45% to 40% change, if you send Red followed by Green followed by Blue then first, two triggers Red intensity falls 40% and then Green fall to 40% and then Blue to 40%.

    (Red,Green,Blue)

     (45%,45%,45%)

    (40%,45%,45%) - 2 trigger

    (40%, 40%,45%) - 2 trigger

    (40%,40%,40%) - 2 trigger

    As I explained earlier one more issue is that - you cannot exactly time current update to particular image. If the trigger pulses are coming in already then any current  update request immediately taken into effect otherwise the request will timeout and skip the update.

    Regards,

    Sanjeev