Making a light switch

Discussion in 'General Electronics Chat' started by Quillion, Dec 28, 2009.

  1. Quillion

    Thread Starter Member

    Jul 18, 2009
    10
    0
    So I am currently trying to make light operated alarm clock, and I already managed to get the most annoying noises possible using 2 piezo buzzers and 2 555 timers, but now I need the switch that would activate the alarm.
    So here is where I am stuck.
    How would I get a photoresistor to act as a switch without the use of microcontroller?
    I need it in such a way that when it reaches certain light level, then electricity will pass, and if its dark then it does not output any electricity.
    I did some research and found out I have to use PNP transistor, but I am still stumped and have no idea how to use it, please help me
    Thanks to everyone in advance who helps
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,866
    990
    I'm just a noob too but did some searching for you and found this.

    http://www.scribd.com/doc/23891342/Photoresistor-Transistor-and-LED-s

    If it is higher current and voltage you want to switch on and off then you could replace the LED with a solid state relay (which is actually a LED to control the "switch").

    Hopefully one of the more experience forum members will weigh in and I have not set you too far astray. :)
     
  3. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    hundreds of circuits that will accomplish this on the web.

    with LDR:

    this one is even animated.
    http://www.technologystudent.com/elec1/lgtdrk1.htm




    or with photo transistor


    [​IMG]

    R1: 100K Pot
    Q1: 2N3904 NPN Transistor or 2N2222
    Q2: NPN Phototransistor
    RELAY: 9V Relay
    MISC: Board, Wire, 9V Battery Snap (if battery used), Knob For R1
     
  4. Quillion

    Thread Starter Member

    Jul 18, 2009
    10
    0
    Thanks a lot to everyone for your amazing help, it was very very awesome and I managed to build it very well, now I wake up every time with the sun, which is perfect since all my uni classes are in the mornings:p
    There is only one problem though, now whenever, someone turns on the lights(in a room near me) my alarm turns on right away. Is there any way to make it turn on a after significant amount of light falls on it rather than when it sees light it gets noisy

    But holy crap I think I created something that is sexually attracted to light hehehehe
    Thanks a lot guys
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    You just need to adjust the sensitivity control to make it less sensitive.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    You can also collimate the light sensor to shield it from room light. Place it in a tube of about the same diameter and aim the tube out the window. Should work better...assuming it's not pointed at a street light. ;)

    Ken
     
  7. foolios

    Active Member

    Feb 4, 2009
    160
    1
    Ahaha, awesome idea. LOVE THIS
     
  8. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,866
    990
    I like the word collimate. :) A new one to add to my vocabulary. :)
     
  9. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    this is cool..

    years ago my dad bought me a beautiful expensive pair of binoculars.
    we lived at the time in the most awe inspiring part of the planet. So exploring the vistas was a way of life.

    anyway, one day I dropped my precious binoculars and whew, luckily I didnt break any lenses or mirrors. But everytime I looked through them for more than a minute, pow, big headache.

    pops sent them in for repairs. When they came back repaired (and working well) I looked at the repair ticket and learned the same word. Collimate.

    I have been waiting for over forty five years now to legitimately use the word collimate in a sentence.

    thank you for the fond memory and the chance to share it!
    and one more time....collimate...
     
    Last edited: Dec 31, 2009
Loading...