1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Light sensor circuit..... sensitivity adjustment using resistors

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by hoghunter, Aug 22, 2017.

  1. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    I have designed this simple dark sensor circuit that will turn on some LEDs at nightfall. After testing, it seems to be too sensitive, meaning it takes a fair amount of light to turn the circuit OFF. This would allow the lights to illuminate well before sunset and to keep working further into the morning. Even sitting on my kitchen table with a light on above, it does does not turn the led off. I have to add a brighter light. And then, just a shadow from my hand will turn it on.
    My question is, how can I adjust the sensitivity to require much less light to turn the circuit off? I'm assuming an adjustment to my resistor combination would do it, but not sure..... thanks.
    P.S. the system is 12v DC

    upload_2017-8-22_18-19-1.png
     
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,370
    Likes:
    974
    Location:
    Loveland, CO USA
    The LM358 will work then the inputs are in between "GND" and "POS"-1.5V. (will not work if too close to "POS")

    You could replace R4 & R5 with a POT. Then you can set the voltage to a different level. (with in limits see above)
    OR
    I don't know which LDR you are using. Try changing R3 to 100k or 1k. I don't know which.
    R4&R5 sets a voltage to 1/2POS.
    R3&LDR sets a voltage.
    The LM358 compares these two voltages.
    So you need to change something in this balancing act.
     
    • Like Like x 1
  3. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    Thanks Ron,
    I'll test some different R values and see what works best. ;)
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas

    I think 47k works well for now. I appreciate the help.
     
  6. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,370
    Likes:
    974
    Location:
    Loveland, CO USA
    Hit the "like" button. I do not know why but I am trying to hit 1000. thanks
     
    • Like Like x 3
  7. AnalogKid

    AnalogKid Well-Known Member

    Joined:
    Sep 22, 2011
    Messages:
    1,137
    Likes:
    161
    Location:
    Ohio - GMT-5
    Interesting way to draw a schematic. Are you in Australia?

    ak
     
    • Funny Funny x 2
  8. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    Haha.... Texas actually.. I'm new at all of this. I guess the pos+ would usually be on top?? :confused:
     
  9. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    Now I'm depressed...... nobody 'likes' me :(
     
    • Like Like x 2
  10. Inquisitive

    Inquisitive Super Moderator

    Joined:
    Aug 31, 2011
    Messages:
    947
    Likes:
    87
    Location:
    Georgia, USA
    Thought I'd add my 1 click(s) worth.
     
    • Thanks Thanks x 1
  11. Reloadron

    Reloadron Well-Known Member Most Helpful Member

    Joined:
    Dec 23, 2009
    Messages:
    6,801
    Likes:
    282
    Location:
    Cleveland, Ohio USA
    I like the name. :) Anyone in Texas going by Hog Hunter can't be all that disliked. :)

    I also gave Ron Simpson a "like" because I like his name (and his post was good).

    Ron
     
  12. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    Thanks guys, I'm a happy camper now!! :happy:

    Reloadron, I'm in Texas now, but was born in Cleveland.... Euclid area ;)
     
  13. Reloadron

    Reloadron Well-Known Member Most Helpful Member

    Joined:
    Dec 23, 2009
    Messages:
    6,801
    Likes:
    282
    Location:
    Cleveland, Ohio USA
    I was NYC born and raised and wish like hell I was in Texas. :)

    Ron
     
  14. AnalogKid

    AnalogKid Well-Known Member

    Joined:
    Sep 22, 2011
    Messages:
    1,137
    Likes:
    161
    Location:
    Ohio - GMT-5
    Born a Buckeye, still a Buckeye.

    ak
     
  15. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    I do like the Buckeye state, but nothing beats Texas ;) Been here since '72
     
  16. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    I do have another electronics question for you guys..... the product I'm putting together requires a 5v step down regulator to power the digispark controller. I am currently using modules to step down the voltage. Can you recommend a simple circuit that I could add to my pcb that would step down 12v to 5v & 24v to 5v?
     
  17. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,370
    Likes:
    974
    Location:
    Loveland, CO USA
    How much current?
    Is heat a problem? (linear regulator like a LM7805 can get hot)
     
  18. AnalogKid

    AnalogKid Well-Known Member

    Joined:
    Sep 22, 2011
    Messages:
    1,137
    Likes:
    161
    Location:
    Ohio - GMT-5
    Little buck regulator modules on ebay are disgustingly cheap, and turning them into a "component" to install on a larger pc board is not difficult. You would have to be building a lot of assemblies to make your own design cost effective.

    ak
     
  19. hoghunter

    hoghunter Member

    Joined:
    Jun 29, 2017
    Messages:
    195
    Likes:
    2
    Location:
    Texas
    Great points. I think I'll stick with the small boards I'm using now. I'll be able to plug them onto the new main board.
    thanks y'all
     

Share This Page