Help with Fiber Optics

Discussion in 'The Projects Forum' started by kunga, Jul 8, 2008.

  1. kunga

    Thread Starter New Member

    Jul 8, 2008
    3
    0
    I'm working on a project that intends to introduce a replacement for the electrical switch due to hazardous issues. I meant by the electrical swich, the one we use at home to switch the lights on/off.
    the replacement will be a fiber optics link fed by a LED and connected to a photodiode. bascially when I press on the fiber link, the light intensity decreases, and the photodiode get less excited (voltage decreases). this property allow me to use a comparator circuit to drive an open loop thing. but my issue is the following. the pressing will be momentarly, like what we do with electrical switches, but I want the effect (namely the light being on) to be constant. and when I press on the fiber link again, the light will be off.

    I hope that clears everything. and I appreciate any help.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can have an almost constant light intensity if you drive the led with a current source. You can build one easily with a transitor or with an op-amp.

    Check this site here
    http://www.allaboutcircuits.com/vol_3/chpt_4/6.html

    If you make this circuit and place a LED between the collector and the positive supply you will will a variable current source (between some limits of course) by varying the voltage at the base.
     
  3. kunga

    Thread Starter New Member

    Jul 8, 2008
    3
    0
    here is a schematic for what i'm about

    [​IMG]


    pressing on the deformer pad on the fiber link, should dcrease the voltage, consequently the comparator will light the LED or Bulb on the extreme right of the schematic. and it will be on until the fiber link is pressed again to turn it off.
    note that the pressure applied is momentarily, as if you're pushing a switch, but the effect (lighting the LED/Bulb) is continous till further pressing.
    I added it to clarify some of my thoughts. appreciating your help.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    This circuit wont work. You have to use RS flip flops to latch your led/bulb and stay on after the deformer has been pressed.

    I was talking about the led which transmits the light throug the fiber optic deformer.:)
     
  5. kunga

    Thread Starter New Member

    Jul 8, 2008
    3
    0
    thanks. I was thinking about the flip/flop but wasn't sure how to approach it.

    I appreciate your help.
     
Loading...