12 V night sensing adjustable photo switch circut

Discussion in 'General Electronics Chat' started by RemoWest, Feb 9, 2015.

  1. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    I have been looking around for a unit/module that switches to 12 V power (at night), when the photo sensor is triggered.
    I have seen quite a few units and schematics online and youtube. I have seen varying designs and configurations on sale on ebay and other sites. ..But none really are exactly what I'm after.

    I have some good basic electronics knowledge, but in no electrical engineer by far. And as easy as this circuit would seem to some, Im lost. My research has left me a bit overwhelmed and confused. Many of the videos and schematics leave alot to be desired. Some use components that others do not. Some list or use components that are unattainable or vague, leading to further confusion. I wouldn't think it would be this hard to do. I feel I've gone as far as I can on my own... I need help. :confused: :(

    What I need is a specific circuit that operates on 12 V, that switches to power at night. And uses a photo sensor that I can adjust the sensitivity on. I need the unit to be as small as possible. Ultimately, I'm powering 12 V lights.

    I figured I should ask here first, as maybe something already exists that can be modified VS designing a new circuit. The only concern I have with using a preexisting unit is possibly the size. I really need this to be as small as possible for my particular application.

    If nothing exists that can be modified, hopefully I can get some of you to show me a design/schematic that would do the trick... And that I could currently get all the parts for.

    I appreciate any and all input on this project. :)
     
  2. #12

    Expert

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    As small as possible? NASA quality, two sided circuit board, with surface mount components serving a custom manufactured IC? Do you need it to include the 12 volt power supply?
     
  3. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    Surface mount components won't be necessary. normal/basic solid state components and standard board will be fine for the application. I plan to use an external 12 V power supply, 1-2 amp... or a 12 V battery.

    P.S. NASA need not be involved...:D
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    How many watts are the 12 volt lamps. Oh, and how many?
     
  5. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    This is where my Ohm's law applies...:confused::eek:

    I don't know exactly is the real answer. I can tell you I am powering a lead of LED lights. The LED's are tiny.I know they will all power-up with 4 button cell batteries, probably way onder an Amp? And I know there are probably 100-200 lights on the spool. I don't know the mA draw per LED though. I know the whole lead of lights powers very brightly with a 1 Amp DC adapter.
     
  6. #12

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    A little googling, a little erasing the extra parts...
     
  7. RemoWest

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    Feb 9, 2015
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    would I be able to use a phototransistor vs a LDR in this? ..That would be my preference.

    Also, I don't see values on R1 and R2 ? I know R3 is the variable resistor.

    Additionally, newbie question. What is the yellow triangle? I used to know.. :):confused:
     
  8. #12

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  9. ronv

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    OK. I think I know the ones, but for $.60 lets do more than enough.
     
  10. #12

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    I am vanquished. :(
     
  11. RemoWest

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    Feb 9, 2015
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    :confused::confused: Did I miss something?
     
  12. ronv

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    Sorry, I just built one for a guy and wanted to get his moneys worth. :=)
     
  13. #12

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    Yeah, ronv just kicked my butt for speed and quality.
     
  14. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    based on asthetice I would like to use a phototransistor if possible.

    I guess I don't get it. :confused: I'm usually pretty quick in that department. This whole thing has me frazzled so that's probably the problem.

    So. I would really like to use a phototransistor for the sensor on this project if possible. Due to it's size and shape it is a lot more applicable than the LDR.
    can the schematic be modified to utilize that component?
     
    Last edited: Feb 9, 2015
  15. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    @ #12

    Ok, got ya..lol

    I'm new here, and still feeling my way around..in the dark. That just threw me a bit is all. :)
     
  16. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    And I thought I knew something when I came here. Now I know even less...Haha
     
    Last edited: Feb 9, 2015
  17. #12

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    Too late. It will already work with a phototransistor.
     
  18. RemoWest

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    Feb 9, 2015
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    Ok. so do I now choose the phototransistor, and then calculate the R1 and R2 values? Could you guys help with that as well? I plan to get the components primarily from amazon/ebay..is that acceptable?


    Should I post the phototransistor. or, I'd rather you make a suggestion per those vendors actually. is that ok?
     
  19. #12

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    There is nothing to calculate. It's all done. Any phototransistor on the Mouser page will work. Probably any phototransistor you can buy will work.

    You might have to change the 56k resistor to less ohms, to make it switch at a higher light level, but that's all I can see left to do. And, no, I can't calculate the resistor for the phototransistor you haven't named or bought yet and the light level that you can't declare and how that unknown part will respond to the unknown amount of light.
     
  20. RemoWest

    Thread Starter Member

    Feb 9, 2015
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    So, we are using the schematic posted by Ronv.. yes?. I thought/assumed the variable resistor in position U1 adjusted the phototransistor sensitivity? Is that still the case, and the 56K resistor may need reduced to affect the variable resistor, or no?
     
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