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Trigger input trouble

Haruhisa Okuda
Prodigy 60 points

Hi,

I use the DLP Light Crafter which synchronizes with trigger input from camera.

Although, I succeeded to make up the system, there is a serious noise trouble.

The problem is that the light crafter reacts unexpectedly when static electricity noise from the human body was added.

I want to know how to avoid such an unexpected reaction. 

For instance, is there any controllable parameters to avoid this? 

  • 0
    Prodigy 60 points

    This is additional information.

    The pico-projector reacts to the very weak static electricity which causes no shock to the human.

    For instance, when we touch the painted metal cover aroud the circuit, it reacts like a touch sensor.

    So, I think the logic of trigger input receiving should judge by the continuous period of the trigger.

    But, there is no parameter to control this.

  • 0 in reply to Haruhisa Okuda
    TI__Genius 9935 points

    Okuda-san,

    Have you closely examined the DLP LightCrafter system board schematic http://www.ti.com/lit/ml/dlpr003/dlpr003.pdf page 13, J7 and U20? It is important to make sure that the correct zero-ohm resistors are installed on the LCr system board (R285 and R282). It is very important that the trigger signal is attached to J7 using a twisted pair, or a shielded cable. The ground connection to pin 4 should be made.

    It sounds like you probably have no ground connection. Please check this.

  • 0 in reply to Pascal DLP
    Prodigy 60 points

    Dear Pascal,

    Thank you for your advice.

    Although we have connected gourd pin(J7 pin4) and used shielded cable, we encountered to the trouble. (Sorry for lack of providing these information.)

    As you mentioned, I will try to install zero-ohm resister on R285. I think that R282 seems to be already installed, by checking the board directly.

    By the way, I want to confirm the connection on J7 when we installed R285.

    Below is the connection when we use input and output trigger. Is that right?

     

    Connector J7

     pin1 camera output trigger -> Light crafter trigger input

     pin2 open

     pin3 camera trigger input <- Light crafter output trigger

     pin4 common ground (camera trigger input and camera output trigger)

     

    Best Regards,

    Haruhisa

     

  • 0 in reply to Haruhisa Okuda
    TI__Genius 9935 points

    Haruhisa,

    Please refer to this app note: http://www.ti.com/lit/wp/dlpa032/dlpa032.pdf

    Also, see the DLP LightCrafter system board schematic http://www.ti.com/lit/ml/dlpr003/dlpr003.pdf, page 13

    J7 pin 1 is VCC. Pin 2 is the LCr input trigger. Pin 3 is the LCr output trigger. However, the wiring can get a bit confusing, because many (most?) cameras use an optoisolator. The Imaging Source camera is such a camera. The app note above shows how to connect to such a camera. This is for triggering the camera from the LCr. It is easier to trigger the LCr from and external source. It just requires a logic (usually 3.3v) signal on pin 2, with pin 4 as ground.

  • 0 in reply to Pascal DLP
    Prodigy 60 points

    Hi Pascal,

    Thank you for the information.

    In your 1st reply, you recommended installing R285 (zero ohm) in order to avoid

    the influence of static electric noise. I want to know how it works to avoid the problem.

    In other words, do you recommended me to use more high voltage input signal? (3.3V -> 5.0V)

    If so, I think that we should install R283 to change the voltage.

    Regards,

    Haruhisa

     

  • 0 in reply to Haruhisa Okuda
    TI__Genius 9935 points

    Haruhisa,

    No, I wasn't suggesting that the trigger signal be changed to 5.0V. You certainly can do so, if your source supports this. I was suggesting that you check to make sure that the zero-ohm jumpers are actually installed. The trigger input is quite sensitive, and I have seen it actually work without the jumpers in place, but it will not be reliable.

    With proper grounding, routing, and jumper installation, the trigger input should work reliably.

    I suggest that if you continue to see problems, you will want to look at the actual signal at the trigger input with a scope to see what noise or impulses may be present.