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Photo sensor

Discussion in 'Sensors and Actuators' started by bumpbump, Jun 13, 2012.

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  1. bumpbump

    bumpbump

    2
    0
    Jun 13, 2012
    HI i am not to experienced in electronics, but i want to make a a photo sensor that when light is on it it completes a circuit.when the light tuns off it breaks the circuit and does not turn it back on until you reset it. could someone show a schematic of something similar.
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    The only wrinkle you will encounter is the latching off after one cycle, not hard to do but you will likely not find a plan with that logic built in... Also you might encounter a nasty bug in a design that is only a single fire and then latching off... If for whatever reason there is a lapse in the light detection (intentional or not) it would go off and not come back on even though it has not completed it's expected on cycle, something as simple as a shadow or fluctuation it the lights intensity would trigger a false premature lock to off... I'm being lazy right now and I would simply suggest you use a 4017 to latch it to off (easy chip for the newbie to understand) anything after the count of one will fail to light it, or you could slightly mod it to light for 2, 3 or whatever number of cycles pretty easily using a 4017...

    Scroll down this page to the one that turns on in the presence of light... That would be one of many light activated switches...

    http://sound.westhost.com/project131.htm
     
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Is there a minimum time duration the circuit needs to be activated once light is detected? What should happen if the reset is done while light is still detected? Should a reset force the circuit off. Should a light-on reset be remembered for the next light-on transition, or should a reset only be accepted during a light-off condition?
     
  4. bumpbump

    bumpbump

    2
    0
    Jun 13, 2012
    this will be applied to a coil gun type devise. when you reset it completes your circuit going to a magnetic coil. when an object travels passed the photo sensor the light is blocked from a laser emitting light on the photo diode. that turns off the circuit powering the coil. but when the object moves past the photo diode it would turn on the coil again pulling back the object. i don't want that so you need to temporally turn off the photo sensor until the command to turn on the the coil is given. i will be using this in a magnetic powered train to see how fast i can get the train analog going. i tried having magnetic contact points on the track but when to train analog got going about 90 mph the wheels did not make good contact. so i much better way is to use photo sensors. it is a straight track about 300 yards long.
     
  5. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    All you need is a single S-R flip-flop or even just a pair of cross-coupled NAND or NOR gates. One side would be controlled by the light sensor while the other side goes to the reset switch. The choice of NAND or NOR will be governed by the HI/LO logic polarity of the light sensor output. The magnetic coil circuit would be driven by the Q or Q' output of the flip-flop as appropriate.
     
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