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External input trigger skipping

nathan klein
Intellectual 345 points
Other Parts Discussed in Thread: DLPC200

Hello,

We are trying to control image change in the DLP via external trigger.

We are using EXP_CON_SYNC_IN0  for this and connected everything properly.

The trigger works but only problem is it looks as if the hardware skips some triggers which resulting in a bad sequence and not as defined in the  LUT.

I have tested the input trigger to the J505 connector with a scope and it looks good.

A typical input trigger is 4 5000 [us] pulses wide separated by a 100[us] .

Id appreciate your help.

Thanks, 

  • 0
    TI__Mastermind 30875 points

    Hello Nathan,

    I am presuming the skip behavior is consistently reproducible. With this assumption I have couple of suggestions and clarifications for you.

    1. What is the pattern exposure selected? 

    4 5000us pulses wide seperated by 100us...

    Basically this will look like 5100us period with pulse width of 5000us. Since the trigger is edge trigger I suggest you to reduce the trigger pulse width as much as possible. Could you try like 10us pulse with same period of 5100us. Let us know if you see proper behavior now.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Intellectual 345 points

    Thank you for the reply.

    I have tried several frame rates and camera exposure times but for all the skipping/ignoring trigger occurred.

    I have also tried to set the pulse width to smaller values with no luck.

    When I use software trigger all is working well.

    Please let me know if you need more information.

    Thank you.

  • 0 in reply to nathan klein
    TI__Mastermind 30875 points

    Hello Nathan,

    There are only two reason why trigger/skipping happens -

    1. Noise in the signal causing DLPC200 to miss or read as false trigger. Please check trigger signal for the noise. Also make sure the Pin#2 of J505 , VCC_EXP is connected with hardware signal reference voltage level (3.3). In short, from the source trigger input side, VCC_EXP, EXP_CON_SYNC_IN0, and if possible connect  DGND point to GND of source.

    2. The pattern frame-rate and camera exposure times are greater than the trigger pulse period.

    I forgot to ask you, have you designed your own board or are you using LightCommander kit?

    Regards,
    Sanjeev

  • 0 in reply to Sanjeev
    Intellectual 345 points

    I have checked the input signal to J505 and it looks clean , also I can see all the pulses.

    I have used J503 for the signals, Pin#2 is connected to Pin#1 of J503 and Pin#6(EXP_CON_SYNC_IN0) also takes its signal from there. 

    Could you please explain how exactly the pattern frame rate camera exposure and trigger pulse period are related?

    We are using the LightCommander kit.

    Thanks,

  • 0 in reply to nathan klein
    TI__Mastermind 30875 points

    Hello Nathan,

    I think I understand your problem.

    On the Kit, the J503 PWM output signals are intended for 'a bit' specific purpose, if you read the spec clearly the PWM period for these I/O lines restricted b/w 0 to 81.88us only, going back to 'specific purpose'  these are for interfacing to low cost LED drivers which accept PWM signals for LED current setting.

    With respect to LightCommander as know the fastest it can go is upto to 5000Hz which is 250us period. So at a minimum a pattern needs 250us time to display, while the J503 PWM can go maximum ~82us, so there is a stream of pulses coming at a different pace than what DLPC200 can display the patterns.

    Use external pulse signal generator and repeat your procedure, it should work, again keep in mind the minimum pattern display time 250us (for 1-bit).

    Regards,

    Sanjeev