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DLPLCR4500EVM: Mirror movement frequency

Sathish Kumar Narayanan
Prodigy 30 points
Part Number: DLPLCR4500EVM

For our application, we need to know what the frequencies are at which the mirrors in the DLP move to generate the different light intensities? we noticed when measuring the DLP intensity that we could pick up periodic modulations of the light intensity, and assume those are generated by the mirrors. For our experiments, we would need to know the frequencies at which these modulations occur -- to compare whether they are in the visible range for our study system.

  • 0
    TI__Mastermind 30600 points
    Hi Sathish,

    With the Lightcrafter 4500, the mirrors move as required to create true 8 bits of light intensity. The frequencies the mirrors move depends on the exposure time of your pattern and the bit depth of your pattern. If your pattern is only 1 bit, the mirrors will only move once for that pattern before the next pattern in shown. For more than one bit, the mirrors will have to move to add those additional bits to the image. I can't tell you exactly what the frequency will be because the bits are not displayed in order.

    What is the frequency of the modulations you are seeing?

    Paul
  • 0 in reply to Paul Goedeke
    Prodigy 30 points
    Hi Paul,

    the modulations we are seeing are around 120Hz (not necessarily periodic in the sense that the "light on" and "light off" invervals are of the same length, but periodically repeating patterns of "on" and "off" that contain generally 120 "light on" and "light off" phases in 1s. The exact type of patterns varies with grey scale value) Our exposure time at 8 bit is 8.3ms, so it seems to be related to the modulation frequency. Could you help me with a better intuition on how the modulations are related to the exposure time? And how this changes for different grey scale values the projector is displaying ?

    Thank you for your help!
  • 0 in reply to Sathish Kumar Narayanan
    TI__Mastermind 30600 points
    120Hz is the same as an 8333us (8.3ms) period. In each period, you'll see the same combination of mirror LED on/off pulses for a given bit depth.

    This means that for 8 bits, you'll see the required number of LED on/off pulses for the device to accurately show 8 bits of information. As you go down in bit depth, you should see fewer and fewer LED on/off pulses until a bit depth of 1, where you should see just 1 LED on/off pulse that corresponds to the period that you set.

    In general, each bit plane is displayed for the following amount of time:
    Bit 1 = 1/2 exposure period
    Bit 2 = 1/4 exposure period
    Bit 3 = 1/8 exposure period
    ....
    Bit 8 = 1/256 exposure period

    However, we don't display the bits in order and so you won't be able to map LED pulses to bit planes.

    I hope that answers your question - let me know if I misunderstood your previous question.

    -Paul