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DLPLCR6500EVM: External trig input low current susceptible to electrical noise

Pedro Ferreira
Expert 1185 points

Part Number: DLPLCR6500EVM

Hi, I want to use the TRIG1_IN signal so that the camera triggers the next pattern in the sequence.

The camera is quite far from the projector (6m cable). So I plug the cable in an opto-coupled camera output and on the other side I have a voltage divider and Zener to lower the output voltage to 0-3.3V

Looking at the DLPLCR6500EVM schematics I see that a SN74LVC1G17 buffer is used at this input. This buffer has an input current of 5uA so I'm afraid that I will have issues with electrical noise. My Interface Device will be connected to the DLPLCR6500EVM via a PicoBlade-to-PicoBlade Off-the-Shelf (OTS) Cable Assembly, Single Row, 50.00mm Length, 6 Circuits. I'm trying to minimize this connection to the projector, will this be enough? What can I do to improve the reliability of this connection?

A simulation of the system is here:

  • 0
    TI__Guru 54675 points

    Hello again Pedro,

    This will depend greatly on how noisy your environment is.  From your simulation, how sensitive will the noise be?  I know that with some of our camera connections we have used cables of the length you mention, but not a circuit like this one.

    Fizix

  • 0 in reply to Fizix
    Expert 1185 points

    Hi Fizix, nice to meet you again, you're on both hardware and software sides like I am :-D

    This is a device for R&D people so it can be installed anywhere from quiet empty room to fairly noisy industrial environment, no need for extremes but we need to protect it anyway.

    I've been advised to use another SN74LVC1G17 on the Interface and place a pull-down resistor on the Projector's connector side so the current in the cable increases.

    And this is the result, I have around 0 to 3mA signal, which is 1000 better ;-)

    It would be great that the projector already have this resistor on these inputs, because they are needed.

    I didn't have much info from Wintech side on the software questions, hope they also see this thread and add some information.

  • 0 in reply to Pedro Ferreira
    TI__Guru 54675 points

    Pedro,

    I talked with one of our EE's here that is familiar with trigger circuits and he agrees that the second circuit is better than the first.

    Fizix

  • 0 in reply to Fizix
    Expert 1185 points

    Great, maybe the next projector hardware version will come with an optional pull-down resistor configurable by mini-DIP switch :-D