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A photocell device to light a small bulb

  1. Apr 15, 2012 #1
    Hello, this is my first post. I googled it, and searched the forums, but no luck.

    I want to know what I need to build a device, that can light a small light bulb. Something rather small, such as a flashlight bulb. But I need the on/off switch to be a photocell that is sensitive enough to make the bulb light, when a laser pointer hits it. If that doesn't make sense, think of it this way. I want a to make a small light bulb light up whenever the laser pointer is hitting the photocell.

    I assume I need a few batteries to light the bulb. Also, a photocell of some kind, but I don't know what kind. Would I need anything else?

    If I need to be more specific about anything let me know.

    Thanks in advance.
  2. jcsd
  3. Apr 15, 2012 #2
    Start with a nightlight circuit and flip the logic (a simple transistor should do), or you could use a comparator and flip the pins.
  4. Apr 15, 2012 #3
    Okay. I guess I should have stated that I am not an electrical engineer, nor do I have very much knowledge on the subject. I am an electrician's apprentice, and I understand ohm's law and comprehend circuits. But I don't know what a logic is, or a comparator is either.

    Also, exactly what would that do? Would that make it so the photocell from the nightlight is switched on when light hits it, or what?

  5. Apr 15, 2012 #4
    Yes - currently nightlights turn the light on in the absence of light.
    You want a circuit that will do just the opposite.

    Essentialy, you just want to invert the signal of a the circuit.
    The approach I was giving you was a simple way to hack something you could inexpensively obtain.

    The quesiton becomes, do you want to build something, or hack something you can buy?

    If you want to build something, I would read on phototransistors and LEDs. That more/less is all you'll need to build your circuit (assuming you have DC power available).
    It seems that you've got some interest in electronics, which is a good start. If you Google night light circuits, you might be able to find something with a full circuit description you can build with a few minor tweaks.
    Last edited: Apr 15, 2012
  6. Apr 15, 2012 #5
    Right. So do you think a laser pointer would be a strong enough source of light to make it work? Do you think it depend at all on the light around the photocell relative to the brightness of the laser? Am I going to have to experiment? Sorry for all the questions. I just have a very specific idea and I want to build it but I don't know exactly how to begin.
  7. Apr 15, 2012 #6
    The laser pointer should be plenty good. It is far brighter then the nominal ambient lighting in a room (which it currently responds to).

    You should always experiment to find out though. It is better to know something will work, than to construct a circuit and hope it works.
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