Photocell activated LEDs using 120v

Discussion in 'The Projects Forum' started by rcrowen, Nov 14, 2008.

  1. rcrowen

    Thread Starter New Member

    Nov 14, 2008
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    Hello, I'm a graduate student at the Academy of Art. I'm working on a project that would use a photocell to turn on/off a set of three 3.2v LEDs. I'm very green at electronics, and thus any and all help will be useful.

    The starting voltage is 120v, but I could possibly use a transformer and drop the voltage to 24 or 12, though I'd prefer to stay with 120v.

    Thanks!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    By not using a transformer, you present lethal voltages to yourself and anyone else poking around the circuit. A wall transformer is so inexpensive and makes the whole project safe to handle.

    There are several ways a photocell can be used. Can you fill us in on the way the LED's are supposed to turn on - gradually, abruptly, with decreasing light, with increasing light?

    Here is a link into out Ebook that talks about LED's and how to size resistors to limit current through them - http://www.allaboutcircuits.com/vol_3/chpt_3/12.html.
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Below are a couple links that could direct you in the right direction with respect to a low voltage solution.
    As far as the 120V method your quoted experience level prohibits me from sharing a solution at this time, especially considering I haven't a clue on the function of your desired circuit. Does it relate to the art project? When and how do you want the three LED's to turn on? Do you want them on for a specific period of time or controlled by the light intensity? Why do you prefer a 120V solution?


    Dark or Light Activated Switch

    Dark Activated Switch

    NOTE: Both the above circuits include relays, but they may not be necessary for your purposes.
     
    Last edited: Nov 16, 2008
  4. rcrowen

    Thread Starter New Member

    Nov 14, 2008
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    I'm working on a night light, and because of it's small size, it's been hard to find a wall transformer small enough to fit inside the lights body. Also, most store bought night lights, which I could take apart, use only one LED, and was hoping to use three or more.

    The LEDs would just turn off/on when it's night or day, though it's an interesting idea to have the LED intensity change with the changing light.

    Currently I'm testing with a breadboard, 12v transformer, 3 3.6v LEDs, and a 68ohm resistor.

    Thanks so much for the replies so far.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    We have a night light we use when the grandkid is over. It's bulb went out, but I was able to get replacement bulbs that use LED's. The diode, resistor and LED are all in the same package. That might be interesting. The bulb base is miniature candelabra. The night light uses a CDS cell to turn on when it's dark, although with LED's, who cares?
     
  6. rcrowen

    Thread Starter New Member

    Nov 14, 2008
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    I was looking at bulbs on superbrightledleds.com. The site mentioned that the bulbs should only be used on a on/off switch system. Think that the photocell would present a problem?
     
  7. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Inside the "lights body"...by this you mean an existing night light housing?
    Check out this site: 3VDC 350ma Power Adapter and look at the dimensions. It is very small! I have a few of these myself with nightlight intentions in mind as well.


    As far as the photocell is concerned most have difficulties switching on in the right "low light-level" condition. I've tries many and on a cloudy day in my hallway their on all day and I certainly do not need the light then. So whether or not you incorporate one in your design is up to you.
     
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