Latency measurement

Discussion in 'General Electronics Chat' started by shambhunath, Jun 4, 2015.

  1. shambhunath

    Thread Starter New Member

    Jun 4, 2015
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    Hello guys,

    i need a suggesation for the measurement of latency between my camera and monitor.
    My camera is HD-SDI CCTV camera and Frame grabber, Nvidia GPU i am connecting between camera and monitor.
    i need to measure the latency from camera to monitor please suggest me the possible way of set up.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,140
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    First I think we need to understand the nature of the connection between the camera and the monitor. Can you give us the physical details of that interface?
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Comparing the camera output to the monitor would be difficult. BAsically, you could point a flash at the camera and a photodetecor at the display, examine the digital video output stream from the camera to detect the change in brightness and time the delay to a similar output from the photo detector. Monitoring the digital video stream for brihtness change will be the hard part.

    Something that might be good enough, and a lot easier, is to time the difference between firing the flash and seeing the result in the photodetector pointed at the screen. The result will include the latency in the camera along with the rest of the system you want to measure.

    A sketch, block diagran, or schematic of your setup would help.

    ak
     
  4. shambhunath

    Thread Starter New Member

    Jun 4, 2015
    3
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    Thank you for replying.
    Yes, your right I need to calculate the time delay between when camera captures the flash and displays on the monitor. But how to measure is the question?
    I have a plan of using oscilloscope which triggers when firing of the flash happens to store the time of input and keeping photo detector in front of the monitor and connecting it to oscilloscope and comparing the final waveforms with the input. Do this work?
    other ideas are also welcome.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes, that should work. The timing resolution will not be very good, but you will be able to see the signal from the photo detector and optimize it for best results.

    ak
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Easy- just get an LED to blink, no need to mess around with a flash unit.
    Connect the blinking LED and photo transistor to oscilloscope, trigger sweep from LED channel.

    Point LED at camera, place photo transistor on display screen, measure delay on scope.
     
  7. shambhunath

    Thread Starter New Member

    Jun 4, 2015
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    Oh really...!! may I know the which LED and photo transistor is to be used...? I mean part numbers if possible.
     
  8. Sensacell

    Well-Known Member

    Jun 19, 2012
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    You can use almost any LED, no need even to build a flasher, just use a switch to turn it on and off.
    Any garden variety photo transistor should work, you might need to experiment with the pull-up resistor values a bit to get a decent signal out of it, but as long as you see something on the scope, you got it.
     
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