Photoperiod Timer

Discussion in 'The Projects Forum' started by WORMSS, Aug 7, 2008.

  1. WORMSS

    Thread Starter New Member

    Aug 7, 2008
    3
    0
    Hello, I asked a friend for some help on a little projects I thought would be cool and suggested you guys would be perfect to help me.

    Ok, I want to make a Timer, [simple enough] but one that is also Sensitive to light.

    The project would be for my plants, so it always has 18 hours of good light, but if the sun is at a certain brightness, turn off.

    I know the first half of this is pretty easy with a simple plug timer, but I am having problems finding one that would also do the Light part of it.

    I always have these "wouldn't it be great" type of moments, and for once I would actually like to actually talk to someone who knows about this stuff to know how easily it could be made by someone who cant hold a soldering iron without burning themselves 4 or 5 times.

    Not asking someone to help design it yet, just how easy of it or if it would be expensive.

    Needs:

    • Turn on at X time
    • Turn off Y hours later
    • Turn off if sunlight is greater than Z
    Optional:

    • Ability to change X
    • Ability to change Y
    • Ability to change Z
    I know all this is simple stuff compared to alot of designs/projects I've seen on here, but we all need to start somewhere. :)

    Thank you for taking time to read this.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can use a 4047 timer IC (http://www1.jaycar.com.au/images_uploaded/CD4047BC.PDF)

    foe the timer. This is good because you can make time delays for several days compared to the 555 which makes time delays for a few hours. For the light level you can use a comparator IC (op-amp) to check the light level with an LDR (light depended resistor) and enable/disable the 4047.
     
  3. WORMSS

    Thread Starter New Member

    Aug 7, 2008
    3
    0
    Ok, I have been reading up and I think I understand how the LDR would work.
    More Light = Less resistance.
    But the Comparator IC was Way over my head.

    But I wasn't quite sure on how the 555 or 4047 actually work.
    I know it works with a Capacitor, and it uses it to count the delay, Bigger capacitor = bigger delay [or the other way around]

    But I was a little unsure of how it would know to count X hours ON, 24-X hours off.

    Sorry I am very n00bish when it comes to actual electronic components, I am more a computer programmer, I could write a program that could simulate all of this, but the actual building of it all is beyond me :(
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can read the datasheet of the components to see how they work and their electrical specifications.

    If you search for 555 tutorial in google you can learn a lot.
     
  5. WORMSS

    Thread Starter New Member

    Aug 7, 2008
    3
    0
    Yeah, I tried that..
    WAY over my head, I had to read a dumbed down "beginners" tutorial on the 555 to understand about the resisters and capacitors.

    The LDR was simpler to understand.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    This should work. The 24 hour timer is the kind you plug directly into an outlet. You can get inexpensive ones that will control up to about 1000 watts of incandescent lamps, maybe more. The relay contacts need to be able to handle at least as much current as the timer.
    You should plug the timer into a GFCI outlet.
     
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