Debris Detector

I have not posted for a while because I am having trouble with my set-up. back in the good old days of pellet work, I'd have trouble and I could figure it out quickly because loading and firing a pellet rifle takes about thirty seconds.


Nowadays, setting up a shot takes a lot longer and it took me quite a few hours to figure out I had a problem.


I am still not sure what's going wrong, but the symptom is that the flash fires the instant the firecracker goes off, not when the debris hits my detector.


So to help figure out whats going on I built up another IR debris detector. Shown here before it gets covered in goo.


The IR LED is hidden on the left arm, the SD5600 detector is on the right arm. All parts are covered with Lexan shields that I have to replace every few months because they get all pitted.


Both the SD5600 and the LED run on 9 volts. the LED is running a current of 100mA and the SD5600 is I don't remember.


These two arm are press fit mounted to a post that I can move further or closer to the target and the two arms are press fit into the tee so I can swing them up and down.


Basically I can put the invisible IR beam as close as I want to the target and the explosion causes debris to cross the beam, making the output of the SD5600 go from 9 volts to zero, which then triggers the flash.


I believe that I measured the delay and it's about 20 usec.


Enough technical gargoyle-isms.



  • Richard Kownacki 3y

    Could it be the shock wave from the firecracker is causing something to move enough for the beam to go out of alignment?
  • Alan Sailer 3y


    I am pretty positive that that is not it, but I think you may have it half right. I do think that the shock wave is moving a faulty electrical connection in the assembly, causing a premature trigger.

    To move the beam out of alignment would be nearly impossible since it is pretty broad. Causing a small change in the beam intensity is more possible, but still unlikely.

    But since I have not fixed the problem, I don't know what it is.

  • ronzzone 2y

    explosive emissions... debris vs. particles ?
    Technically, "particles" resulting from the igniting firecracker may, actually, be triggering your camera axe-strobe.
    Consider;... The speed of light vs the speed of anything else.
    Most (any?) explosive material, when ignited, will emit a very intense, (and quick), burst of light "particles", (ie., photons), before any shock wave, audible sound, and/or, any physical particles(ie., debris) are emitted, and/or detected.
    So, Your infrared detector, maybe, ( is, imho) responding to the flash of light emitted from the firecracker itself., as it explodes...(?)
    ...could try shielding the detector more...but, that will most likely result in a smaller area for detecting any of the debris you want to detect...(?!)

    Regardless, blowing things up with firecrackers and photographing the same is always fun! especially when getting consistant, and waaayy cool, results! Like yours, for sure!!
  • Alan Sailer 2y


    It had occurred to me that the light from the firecracker was causing problems.

    My style of working (trial and error) often doesn't allow me to come to definite conclusions. Running test shots consumes a lot of time and resources.

    However, my trigger was failing with shots that emitted a lot of light and shots that did not. So I kind of ruled out light as the false trigger.

    The biggest change since this post was eliminating the lexan shield on the right side. It gets scared with impacts from debris. I believe that the shock wave from the explosion was causing the shield to vibrate slightly and with all the dings on the front, changing the intensity of the IR light, causing a premature trigger.

    I am now using a thick glass widow set inside the PVC fitting. My triggering has been very robust.

    This will not last though.

    My one constant with high speed work is that something is always going wrong. I have never had the perfect error free set-up.

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Taken on August 1, 2012
  • ƒ/3.5
  • 13.8 mm
  • 1/30
  • 800
  • Flash (off, did not fire)
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