98 Comments

  1. January 17, 2011 at 4:23 pm

    Conagh Power

    this website has helped me a lot with my course work.

    Reply
    1. October 3, 2013 at 12:10 am

      Trev Welto

      Hi i have a 4 kw solar pv system and i am looking to buy/build a dark/light sensor switch to use as a switch, in line, into the domestic supply to turn on and off an electric oil filled radiator rated 1 or 2 kw, when the solar panels are generating enough power to run the heater. So I don’t have use energy from the grid..
      Can anyone help?

      Reply
  2. January 28, 2011 at 5:46 am

    Amdani Wijaya

    Today, I want to make automatic switch, to turn on my car head lamp based on this dark sensor. Is this your scheme can be recommended for that?
    Actually, I’ve done this experiment from your scheme. With a relay (instead of LED), I hope my plan worked.
    Apparently, I have problems; at the time of the light intensity changes gradually (in the afternoon), or at the time of the transistor base current for the process began to get saturation, relay shaking, of course, my bulb flashes great, even broken.
    Do you have any suggestions to solve this problem?

    Thanks & Regards,
    amdani

    Reply
    1. January 28, 2011 at 11:08 am

      admin

      Yes, i do have solution for this problem, if you make 741 based dark sensor, the relay does not shake or flicker/flutter. You can get the circuit here: http://www.ldrengineering.org/dark-sensor-using-741/
      Please wait till 29.1.2011 so that I can make it an show you on video. Please ask if you have other questions.

      Reply
      1. October 28, 2012 at 9:10 pm

        Herbert

        I try to click the link for dark sensor using 741 but is unavailable. My relay flickers. Help. Thanx

        Reply
  3. January 28, 2011 at 1:07 pm

    Amdani Wijaya

    Thank you very much for your quick response.

    I will soon try the circuit.
    If I use a 12 volt battery, what components need to be changed?

    Thanks & Regards,
    amdani

    Reply
  4. May 30, 2011 at 10:06 pm

    Isaac Sandy

    I want to make a dark sensor that turns on 1 led when it is dark, another when the light is ambient, and one final led when it is bright. I havent been able to find any circuit based on this description on the internet and I wanted to know if I could get some pointers.

    If it isnt possible, im okay with that! I just want to know if it is possible in one setup or if I need to make 3 sensors operate 3 individual LEDs, and if I can; could I be led to a link of the circuit? Im aming for something small and something I can enjoy making for myself.

    Reply
  5. July 30, 2011 at 12:14 pm

    ahsan

    i wanna circuit to glow 100w bulb in dark senser with the help of DC voltage.

    Reply
    1. July 31, 2011 at 10:20 am

      LDRENGINEERING.ORG

      Well, you can do that using a relay. It is quite simple. see this example: http://www.ldrengineering.org/how-to-use-a-relay/
      This page gives you the idea for using a relay and using 100W(AC bulb) operating with a DC based dark sensor. Be careful while using 220V AC.

      Reply
  6. September 27, 2011 at 4:01 pm

    taghag

    hi there – great little circuit and easy instructions, thanks!

    Reply
  7. November 9, 2011 at 10:50 am

    shehryar naveed

    thnx i will try it inshaallah

    Reply
  8. November 17, 2011 at 8:40 pm

    evill

    i want to make a lamp for my aquarium with dark sensor. i want to use 6 white leds 5mm..can u pls post a diagram for me to follow. thanks

    Reply
  9. December 1, 2011 at 2:45 pm

    Manzoor

    thnx i will try it inshaallah gr8

    Reply
  10. January 10, 2012 at 7:45 pm

    lanny gibbs

    can you show me a digrame of how i can make a automatic dark detector 12v dc using a led tail light thank you and god bless

    Reply
  11. January 15, 2012 at 6:03 pm

    mukesh jaiswal

    i want to make a sensor siren using LDR .can u sent me a diagram please.

    Reply
  12. January 25, 2012 at 11:08 am

    rizwan

    MY Group make this project…..<3<3

    Reply
  13. February 2, 2012 at 3:45 pm

    rexleeguzman

    Sir…can i make a color sensor composed of red, green, blue, yellow, and orange.

    Can i use these LDR’s to make a color sensor like these?

    And can u help me make a schematic diagram on these.

    Thankz You…

    Reply
  14. February 14, 2012 at 10:57 pm

    park47

    Thanks, after a long search…this is the most complete DIY exist. I could successfully done both L/D sensor.. 🙂

    Reply
  15. March 1, 2012 at 3:05 am

    Jim

    Hi, I want to build a circuit that will turn a small motor in one direction when light is present and then reverse the motor when the light is out.

    This circuit will be used to open a door in the morning when the sun comes up. After the door is completely open, it will trigger a limit switch to stop the motor. When darkness falls, the motor will need to run in reverse to close the door. When the door is closed, it will also need to trigger a limit switch to stop the motor.

    Is this possible? Thank you!

    Reply
  16. March 6, 2012 at 7:39 am

    Geo

    can you make the dark sensor work with the joule thief?

    Reply
  17. May 5, 2012 at 9:18 am

    ram

    tanx a lot………..

    Reply
  18. May 24, 2012 at 5:07 pm

    Manish Datta

    Thanks man! It is surely the most simple and the best explanation for a dark/light sensor! I want to light up more than one, say 3 LEDs in this way. Any changes to be done? Thanks in advance buddy!! 🙂

    Reply
    1. May 24, 2012 at 10:17 pm

      Sagar

      If you are keeping 3 LEDs in Parallel, then, use another transistor, for example, BD139. and if you are keeping LEDs in series, you don’t need to make change. I recommend for series.

      Reply
      1. May 25, 2012 at 10:44 am

        Manish Datta

        Should I use a 9V battery or let it remain the same?

        Reply
        1. May 25, 2012 at 5:59 pm

          Sagar

          keep 9V

          Reply
  19. June 12, 2012 at 6:57 pm

    Good Or Bad

    Can please tell me the pin configuration in details of BC547…Please

    Reply
  20. June 30, 2012 at 10:40 am

    Ridwan

    Hi my brother, i am very impressed with your site. Can you help me with how to use ldr with atleast 40 leds for security lights

    Reply
    1. June 30, 2012 at 12:07 pm

      Sagar

      You need to use a dedicated “LED driver” and a microcontroller for controlling at least 40 LEDs or, you need to have a power transistor that can take up to 2 Amp.

      Reply
      1. September 21, 2012 at 1:18 pm

        Hafz

        hye mr admin..can u help me how to make dark sensor using relay..the relay must Normally Open when connected with 5WATT Solar Panel (Max. Voltage: 17V, Short Circuit Current: 0.34Ampere.)..Tq..What type of relay i need to use for this low power solar panel for switch the relay..

        Reply
  21. August 1, 2012 at 2:48 pm

    akhiran

    I am using the same configuration but using lm741 as comparator. The output of that will light an LED strip. I want to usr RC circuit to fade in and out that. What type of transistor do I need? Can you draw a schem. Thanks

    Reply
  22. August 24, 2012 at 5:10 pm

    Sweatha.J

    hi sir, i need a theoretical proof for the values of the resistors used in this two circuits. this is quite a useful start for the beginners! nice job sir! help me out as soon as you can!

    Reply
  23. August 29, 2012 at 4:59 pm

    Dylan

    I want to know what is the resistance of a LDR in the dark and the risistance in the light..can any one tell me???????????

    Reply
  24. September 5, 2012 at 3:02 am

    hesham

    hi very nice video but can you till me is the same if i uesing 2N3904 Transistor

    OR WHAT type i can use for this

    Reply
  25. September 19, 2012 at 4:32 am

    Ibrahim NM

    Thanx alot.can u help me with acircuit diagram for adark sensor do

    Reply
  26. October 2, 2012 at 8:15 am

    Anurag Shukla

    dear sir i currently saw your video on light sensor on youtube , i need to make this for my project so kindly can u give me the materials required to make it as i am unable to figure out the materials in video
    Thanks!

    Reply
    1. October 2, 2012 at 12:29 pm

      Sagar Sapkota

      You can see the components required on the schematic.

      Reply
  27. October 7, 2012 at 2:23 pm

    Akshay

    WHAT CAN WE USE INSTEAD OF A 330 OHM RESISTOR ?
    PLEASE HELP ! 🙁

    🙂 THANKS

    Reply
    1. October 7, 2012 at 9:38 pm

      Sagar Sapkota

      you can use any resistor between 220 Ohm to 1Kilo Ohm

      Reply
  28. October 22, 2012 at 9:57 am

    pratik

    sir pls give me a ckt of light/dark sensor using opamp-LM358….in urgnt need for it….pls help me out sir…

    Reply
      1. October 24, 2012 at 10:57 pm

        pratik

        thnx for d link sir!!!
        i made d ckt using LM358 n it’s functioning properly…but sir, dere’s 1 thng i wanna tell u that
        even a 5th grade boy wud do d connectns if v gave him some basic tips n ckt diagram, but
        being a future engg 1 shud know y is this happening….dis thot haunts me a lot…
        thr4 1 request u if u can tell me d working of dis ckt…..i tried to figure out bt got
        confused in no. of points…. i wud b very thnkful to u sir….
        PLS help me out…

        Reply
        1. October 25, 2012 at 8:52 am

          Sagar Sapkota

          You need to learn about operational amplifier. You can start with LM741 operational amplifier(op amp). Try to understand the description of this project: http://www.buildcircuit.com/dark-sensor-using-741-2/

          If you understand this you can also understand the working LM358 because it is also a type of op amp. The simple circuits have been published on buildcircuit for electronic starters. If you are studying in school, just focus on learning about components. There are several things you need to learn, so wait till you join engineering.

          Reply
      2. January 17, 2013 at 12:54 pm

        jyothi

        sir i want to generate emf of south and north pole in coil using operational amplifier lm393
        and also want to generate emf in a coil circuit of 2 volt

        Reply
  29. October 25, 2012 at 9:05 am

    ike

    i’m supposed to make a simple darkness activated alarm using a power of 6v..can you help me out?

    Reply
  30. October 29, 2012 at 4:21 am

    massage

    Nice post. I was checking continuously this blog
    and I’m impressed! Extremely useful information particularly the last part 🙂 I care for such info a lot. I was seeking this certain info for a long time. Thank you and best of luck.

    Reply
  31. November 9, 2012 at 9:48 pm

    Suyash Agrawal

    Sir, i am a beginner in electronics and i am going to make this but i wanted to light up more LEDs instead of just one…so should i use a resistor of lower resistance and if yes then where should i place it or should i use a trim pot or potentiometer?? please help

    Reply
    1. November 9, 2012 at 9:53 pm

      Suyash Agrawal

      Nevermind sir i saw the comments and figured it out but please help on this thing that if i connect my LEDs in series will not their brightness decrease and if yes then please recommend a solution..

      Reply
  32. November 13, 2012 at 3:50 am

    Azman

    need some pointer here. I’m building an automatic light system which need to be shutoff during night time. i believe i have some idea on that part using simple connection through a relay. however i’ve to depend a car battery. so my question is how do i size up the circuit so it can take up higher amp and volts. thanks in advance.

    Reply
  33. November 26, 2012 at 4:38 pm

    Armughan

    Can i use 100 ohms resistor for 100k resistor

    Reply
    1. November 27, 2012 at 9:18 am

      Sagar Sapkota

      no

      Reply
      1. November 30, 2012 at 1:06 pm

        Armughan

        not working?why

        Reply
  34. November 27, 2012 at 10:29 am

    NAVEEN

    sir i need dark detector without bread board

    Reply
  35. December 5, 2012 at 7:52 am

    PS

    Hey, can I use SL100 instead of BC547?

    Also, I saw a couple of links that showed making the same thing using two transistors? One transistor will do right?

    Reply
    1. December 27, 2012 at 12:16 pm

      Sagar Sapkota

      yes one transistor will also work. you can use SL100 also.

      Reply
  36. January 2, 2013 at 10:30 am

    vanshika goel

    if i use greater or less than 6V battery will it work? why different resistors are used?

    Reply
    1. June 20, 2016 at 8:50 pm

      Zevious

      You can use any voltage that doesent burn out your LED. Remember V=IR so you may want to increase your resistance.
      The Differant resisters adjust the sensativity of the phototransistor so if you change those values it may always stay on, or need very bright light.
      It would also be smart to incorperate hysterisis so you dont get flickering when the current is “just” right.

      Reply
  37. January 2, 2013 at 10:36 am

    vanshika goel

    i have made a automatic light sensor .if i use greater or less than 6V battery will it work? why different resistors are used?

    Reply
  38. January 7, 2013 at 10:44 pm

    akhilesh

    sir,
    hw to use this circuit with 12V DC and use 3-5 LED, plz reply me soon

    Reply
  39. January 7, 2013 at 10:47 pm

    akhilesh

    Sir,

    can I run this project with 12V DC, and want to use 3-5 LED(Big size) use as emergency light.

    Reply
  40. January 15, 2013 at 5:12 am

    sha

    hai can u help me how can i use only one calculator as my counter and decounter

    Reply
  41. January 25, 2013 at 9:19 am

    alfirdaus

    what should I do if I want to use 220VAC power (for Automatic Light Sensor function)?

    Reply
    1. May 6, 2013 at 2:11 am

      sisco

      add a relay to the output with a protection diode in front of the relay or search for connecting a relay on google and you will understand better.

      Reply
  42. February 5, 2013 at 10:57 am

    rotnodeep

    sir this video is very helpful bt pls sir i wnt the working of dark sensor today only as soon as possible … as tomorw is my practical nd i hve made this circuit nd it is now working bt i dont know how it is working…. thank you sir

    Reply
  43. February 8, 2013 at 5:19 pm

    sudhanshu

    what would happen if i use 1k ohm resistance instead of 100k ohm? please reply ASAP

    Reply
    1. February 8, 2013 at 8:23 pm

      Sagar Sapkota

      check yourself. or check here: http://www.buildcircuit.com/voltage-divider-rule/

      Reply
      1. February 10, 2013 at 4:42 pm

        sudhanshu

        thanks sir, i finally made it. the video tutorial was really helpful. great site! thumbs up!

        Reply
  44. February 8, 2013 at 5:36 pm

    sudhanshu

    also, if i connect collector and emitter in opposite way you have connected?

    Reply
    1. February 8, 2013 at 8:22 pm

      Sagar Sapkota

      It does not work that way.

      Reply
      1. May 1, 2013 at 12:03 pm

        Jean claude

        How to combine the dark and light sensor

        Reply
    2. June 30, 2014 at 6:37 pm

      JERIN

      i have connected emitter n collector in opposite way n it works why?

      Reply
  45. March 3, 2013 at 3:36 pm

    Srinagrao

    Which transistor to put if i want to run a DC motor instead of a LED.?? reply fast pls… imp
    ……

    Reply
    1. May 29, 2013 at 7:03 pm

      Vijay

      Use a mosfet IRFZ44 or 2n3055 based on the current rating of motor.

      Reply
  46. March 31, 2013 at 11:45 am

    inno_han

    sir..
    i follow your circuit in the video,but it doesn’t work..
    i also do the automatic dark detector circuit on the breadboard but replace the transistor with 2N3904/BC547..
    But,it work reversely..the led turns off when dark..
    can u help me how to do it properly?

    Reply
    1. April 18, 2013 at 8:18 am

      Elizabeth

      Maybe the terminals at the end of the breadboard are not connected..
      We try it also and it doesn’t work. But after we troubleshoot it, we saw the ends are not connected.

      Reply
    2. April 23, 2013 at 12:12 pm

      Shakil

      It’s cause the transistor. Try to put B,E,C correctly.

      Reply
  47. April 23, 2013 at 8:33 pm

    Sarang Agrawal

    Very good circuit !!!! Really helped me in my first project!!!!

    Reply
  48. May 1, 2013 at 8:10 pm

    Devil

    Hi, I would like to ask why transistor is needed for lighting up the LED? Since LDR has almost similar characteristics as a variable resistor, through voltage divider rules, LED still turned on, right? Hope to receive your feedback. Thanks.

    Reply
  49. May 2, 2013 at 7:12 pm

    hex dumbbells cheap

    You could possibly have a fixed or perhaps the
    adjustable form.

    Reply
  50. August 13, 2013 at 3:23 pm

    Muhawe Gilbert

    Dear sir,
    How many bulbs or lamps can the above dark light detector control?Can it be modified to handle strong lamps?If yes help me with materials used thanks

    Reply
  51. August 26, 2013 at 11:53 am

    chelsea

    can i use a 9v battery instead of a 6v power supply

    Reply
  52. August 26, 2013 at 11:55 am

    the gig

    sir
    can i use a 9v battery instead of a 6v power supply

    Reply
  53. August 30, 2013 at 5:36 pm

    naman

    yeah..i..build..it

    Reply
  54. September 15, 2013 at 5:39 pm

    IBRAHIM

    if i connect a buzzer in series with led …will it work…mean…b/w led and transistor i give a connection to buzzer…plz reply its urgent…..

    Reply
  55. September 21, 2013 at 7:27 pm

    Satish

    Hi i wanna circuit to glow 100w bulb in dark sensor with the help of AC voltage. i want to use transistor instead relay.

    Reply
  56. September 26, 2013 at 5:37 pm

    Karina Sena Gomes

    Thank’s so much!!

    your tutorial is the best!!!

    Reply
  57. December 2, 2013 at 8:26 am

    دروس وشروحات يشمل برامج مجانية تحميل برامج استرجاع الملفات برامج تعد

    Important data. Lucky myself I found your website by accident, for dismayed precisely why this coincidence couldn’t occurred in advance! I actually added the item.

    Reply
  58. December 21, 2013 at 12:59 pm

    Girish

    Hi…. In this dark sensor circuit .. i want to illuminate the led using AC supply and not the dc voltage…. Can anyone help me out with this

    Reply
  59. January 27, 2014 at 10:34 am

    San Miguel Beer

    ne555 ic and a 100k pot also work right?

    Reply
  60. February 24, 2014 at 5:58 pm

    sahasraka

    I want to run a 9v motor instead of a LED in the Dark Sensor. can you please send me the materials wanted?
    pleeeeeeeeeeeeease!!!!!

    Reply
  61. February 25, 2014 at 9:40 am

    Nupur jain

    Can i use 1.2k resistance or 0.6 k ..?? My circuit is not working

    Reply
  62. April 9, 2014 at 12:59 pm

    air max de nike

    Dark/Light sensor using transistor | BUILD CIRCUIT
    air max de nike http://www.aguasdealcala.es/zapatillas/air-max-de-nike.html

    Reply
  63. April 17, 2014 at 5:39 pm

    Prajwal

    First of all I wanna thank you. This circuit is really working fine. But, instead of led, i wanna replace that with 5v DC motor. I replaced BC547 with 2n3055. But it is not providing sufficient current to drive motor. Should I use SL100 ? Could you please help me out with this ?

    Thank You,

    Reply
    1. October 20, 2014 at 9:35 am

      Amar

      You could use the darligton pair transistor BC517 to fire 2N3055 which would in turn drive the load.
      That should work fine for your motor.

      Reply
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  65. July 9, 2015 at 6:15 am

    Maneeshwari

    I want to make an dark detecting sensor. I want to make some changes like in place of led I want a buzzer. How to choose a good buzzer??? It’s for my school project to make security system

    Reply
  66. September 2, 2015 at 6:24 pm

    shaakir

    Do you have to use a breadboard to build a darkness detecting sensor

    Reply
  67. July 11, 2016 at 6:11 am

    Aravindhan

    In my dark sensor light was on always I don know I am using your circuit why light is on

    Reply
  68. October 23, 2018 at 2:04 am

    cbpelto

    RE: Solar Panel Controller ‘Shut Off/Turn On’ Photosensor

    SITUATION: Solar Panel Controller doesn’t function properly after the Sun comes up.

    BACKGROUND: At a remote mountain location, I have a solar panel array to provide electrical power. It works well. However several lines of PWM controller units all have the same problem. When the Sun comes up the next morning, the controllers ‘misbehave’. Instead of reading 14V going into the battery array, they read 24V and the batteries don’t charge. They drain. When I disconnect the controller from the panels and reconnect it, then it works just fine.

    The panel array provides 100W at 12V.

    SOLUTION: Get a photocell switch that disconnects the controller from the panels after Sunset and reconnects after Sunrise.

    PROBLEM: There is no such beastie on the market. They are all DUSK-TO-DAWN. No such critter as a DAWN-TO-DUSK.

    CONCLUSION: I have to DIY.

    This site’s article provides me with the basic information I need. But not being a Double-E major [I’m Microbio] I’m having to educate myself.

    QUESTIONS: For this situation:

    [1] What resistor is necessary for R1 470R?
    [2] What resistor is necessary for the VR1 10K?
    [3] What transistor is necessary to Q1 BC 547?

    Reply

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