pulse timer/switch

Discussion in 'The Projects Forum' started by chazam, May 19, 2013.

  1. chazam

    Thread Starter New Member

    May 19, 2013
    2
    0
    I have a project which is defeating me. Trying to relearn what electronics I knew 50 years ago when transistors looked like garbage cans next to todays mini components has been a challenge. (I am within sniffing distance of no. 80)
    I want the interruption of a light beam, 1 mm or less travel, to trigger a single on/off switch cycle with a duration adjustable and repeatable from approximately 1 to 30 milliseconds, with no delay. This cycle might be repeated in a week, or every 30 milliseconds. The switch should handle up to 500 mw.
    I know this is not breaking new ground, (monostable multivibrator chip?), but any help would be much appreciated. If you guys see any flaws in my thinking, please feel free to comment.
    This is to be used for pulsing a diode laser.
     
  2. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    The light beam would be created by an LED and sensed by an LED sensor (you buy them as a pair). The sensor needs to be connected to a Schmitt trigger to see only one change in the intensity of the beam. The output would be connect to the 555 timer's trigger, which is configured as a 30 ms one shot.
    Well, it's not zero delay, but it is in the order of ns. :)
     
  3. edwardholmes91

    Member

    Feb 25, 2013
    181
    18
    You can even get them as one thing I believe. And then use a bicycle reflector type material to bounce the beam back. LDC3's idea seems pretty close to me.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Could you use a slotted opto or have you got more distance between the light source and the detector?
     
  5. chazam

    Thread Starter New Member

    May 19, 2013
    2
    0
    Many thanks for the quick replies'
    A B i g apology for my slow response, but all kinds of stuff seems to interfere with my projects.
    LDC3--the trigger duration has to be variable because I don't yet know how long the pulse has to be. As far as delay, time is relative. To me, a ns is a figment of someone's imagination, <1ms should be more than good. Configuring the 555 will be my big problem. As I said, I come from the Stone Age of solid state electronics, the CO2 laser I used was the size of a can of tennis balls.
    Edward---having the LED and sensor as a single unit would be a great spacesaver.
    Dodgydave---unless I misunderstood, which is more than possible, the slotted opto does not have an LED incorporated. It would be nice if it does.
    chazam
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,976
    744
    Yes it does have an LED and Photo transistor
     
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