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Need help with LED flash trigger for camera

Discussion in 'LEDs and Optoelectronics' started by Santosh Shetty, Feb 7, 2016.

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  1. Santosh Shetty

    Santosh Shetty

    2
    0
    Feb 7, 2016
    hi guys, am an amateur photographer with zero knowledge in electronics and a shoe string budget.... am tryinv to build myself an LED based flash made from a 100w LED
    Q1 ) why 100
    A) well it helps kill yhe ambient light such as the sun when shooting in broad day light)....
    Q2) why LED
    A) i think i might be able to build an LED based light torch aa its simple and leds are cheap rather and easier to build compared to a xenon circui
     
  2. Santosh Shetty

    Santosh Shetty

    2
    0
    Feb 7, 2016
    am trying to build a simple way of triggerinv the led flash since this wud mean the led will only be on for a fraction of a sec and thus give me prolonged battery light instead of running the light on for long stretch and drain the battery...but then if i need the led to flash ut needs to synch with the camera when the camera button is pushed....thiz is whete i need you guys todvise me
     
  3. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    I've only seen cameras with external components that allow the flash to go off at the same time as it's pressed (camera dependent)

    So unless you hack it....
     
  4. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    The camera's synch terminal, either on the hot shoe or a separate connection is the way to synchronize the flash to the shutter. Assuming that you DO NOT want TTL control of the flash output, then you can adjust the output of the LED by pulsing it on for a varying duration. Let's say 1/10000 second is the low power setting, then 1/1000 second could be a high power setting. There won't be a linear relationship - you'd have to use trial and error to figure it out. A 555 timer IC in monostable mode driving a transistor switch can work (see the first link below). The thing about pulsing a LED for very short durations is that they can take a lot more current - ie: They'll be a lot brighter. Something like 300% of their maximum rated continuous current according to the second article below.

    So, the camera's synch terminal is just a switch. This is used to trigger the 555 monostable to produce a single short pulse which turns on a transistor switch which turns on the LED (via a resistor to limit the current to a safe level) for the duration of the pulse. The pulse is short - 1/10000 second say. A resistor and capacitor in the 555 circuit determine this duration.

    Camera's usually synch at shutter speeds from 1/60 second to 1/250 second - so much longer than the flash pulse.

    http://www.electronics-tutorials.ws/waveforms/555_timer.html
    http://www.cree.com/~/media/Files/C...Lamp Application Notes/XLampPulsedCurrent.pdf

    This should whet your appetite for now. Come back when you're a bit further along...

    And don't forget there are LOTS of commercially available LED flash units - if you get stuck... or want something that works straight away. And XENON flash units are very cheap too - (esp if you can get hold of those old disposable cameras with flash).
     
  5. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    Wait... just thinking about your original post... What sort of 100w LED are you actually talking about?

    I have this sinking feeling that you mean the household type of 100w LED lamp (actually 20w)? If that's the case, then you can't pulse those in the way that you want - sorry.
     
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