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Day Night Activated Triac Switch Circuit

Last Updated on September 11, 2019 by Admin 22 Comments

The purpose of the discussed triac based day night activated switch circuit is to automatically switch OFF a given  electrical appliances and peripherals during day light and vice versa, this could be a lamp, an alarm, etc.

triac

Generally speaking, this is a type of photoelectric relay which is driven directly through the home's mains electrical system, with no need for any kind of mechanized device like relay or other component.

This day night switch circuit using triac and LDR is extremely straightforward, therefore its inexpensive and simple to build, only there exists one particular drawback, it is not flexible and is not going to enable electronic adjustments to drive or modify the switch. That, by the way, is not a mechanical switch, rather an SCR or triac.
Photoelectric relay cell
Interconnection of a photoelectric relay cell
Photoelectric relays

There are numerous remedies developed to automatically switch off the lamps as soon as it's dark. Generally we require a DC power supply and an electromechanical relay, however in case you come up with a circuit which can be directly coupled to the AC power supply, the quantity of components necessary is usually minimized down and that is exactly what reveals in this project displayed below.

day night automatic triac switch circuit

The key component of the day night triggered triac switch circuit is a LDR photoresistor of sensitive resistance, resistance in Quebec may differ its resistance According to the strength of the light it obtains, it possesses a resistance of 200 ohms at nighttime and during daylight a few thousand Ohms.

The capacitor C1 is a voltage divider for delivering the photosensitive LDR and the triac gate.

In Normal light, voltage declines as LDR resistance diminishes, however, at night, resistance to photoresistor gets higher, causing improved triac activation current, operating and lights.

Parts List

C1 = 105/400V PPC capacitor

R2 = 1K, 1/2 watt

LDR = high sensitive type

Triac = BT136

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About Admin

Hey friends, Thanks a bunch for stopping by this site! I am an engineer with a Bachelor of Engineering in Electronics and Telecommunication. One of my passions is gathering information from all sorts of electronics books and tutorials. I then take that information and compile it into a language that is super easy to understand. My goal is to make those complex electronics circuit concepts and technical terms much more accessible for all the new and budding electronics engineers out there. I can also design customized circuit diagrams as required by the users.
If you have any questions related to this field, please do not hesitate to drop a comment! I am always here and ready to help you out with any queries you might have. I cannot wait to hear from you!

Reader Interactions

Comments

  1. Deodati joseph says

    May 18, 2023 at 12:03 am

    the design can’t be accepted by engineers. ldr can not be operating directly from 220v

    Reply
    • admin says

      May 20, 2023 at 10:09 am

      There is a series capacitor with the AC mains, so no issues at all.

      Reply
  2. seonha says

    November 25, 2021 at 9:25 am

    Can you explain why this works, for defense purpose, thank you for answering

    Reply
    • admin says

      November 26, 2021 at 10:45 am

      This is a very crude circuit and I won’t recommend it for defense applications.
      During day time, the LDR grounds all the supply, and prevents the gate voltage to the triac and therefore the triac and the lamp remains switched OFF….at night the LDR resistance becomes high enough, and the current from the 105 capacitor is able to reach the triac gate and turn it ON.

      Reply
  3. Ravi says

    September 24, 2019 at 9:11 pm

    this circuit…are work led bulb….im make this circuit but..1k resistane verry heat..

    Reply
    • admin says

      October 9, 2019 at 10:18 am

      use 2 watt wire wound type

      Reply
  4. Avi says

    September 9, 2019 at 5:03 pm

    is it possible to put a variable resistor and what value it should be ?

    Reply
  5. Vilas Ramchandra Khare says

    October 8, 2018 at 11:38 am

    Sir, there are various remarks i.e. results have received from the hobbyists who are assembled this circuits. My request is there i.e. after receiving the results, Admin. has suggested few changes like value of resistance / lDR etc. So my suggestion is that , after proper checking and sufficient time over of particular circuit, then this may be published. if my suggestion is found proper then please do the needful. Thanks.

    Reply
  6. Gordon says

    August 22, 2018 at 7:04 am

    ? 240 volts or 100 volts supply ?

    Reply
    • admin says

      August 24, 2018 at 7:27 pm

      both should work….

      Reply
  7. Shaji says

    June 23, 2018 at 12:41 pm

    Light is working, But in LDR shows sparking some times. why?

    Reply
    • admin says

      June 23, 2018 at 1:57 pm

      use a bigger LDR, t is happening due to current in surge from the capacitor

      Reply
  8. Baig says

    June 3, 2018 at 1:08 pm

    I tried this circuit but it didn’t work. R1 heats up within no time.

    Reply
    • admin says

      June 4, 2018 at 9:33 pm

      try 4k7/ 5 watt for R2 and select an LDR which shows around 1K resistance at ambient day light

      Reply
  9. Abdellah says

    October 30, 2017 at 9:40 pm

    Le fonctionnement automatique du circuit est difficile à croire. Étant donné que le triac ressemble à un interrupteur électronique (irréversible ) c’est à dire qu’une fois amorcé il persiste en état de conduction même si le courant de la gâchette est coupé. Vu cette caractéristique propre au triac , la commande automatique à travers un tel composant s’avère non convenable . Car la gâchette recevant l’impulsion suffisante imposée par la LDR fait déclencher le triac puis redevient insensible à toute variation ohmique de la photorésistance. En résultat l’ampoule s’allume et le système électrique reste activé indépendamment de la quantité lumineuse incidente jour et nuit sur la LDR , à moins que le triac soit isolé du secteur pour se remettre hors service . Il y a lieu donc de modifier la commande automatique de ce circuit au biais d’une alternative basée par exemple sur un MOSFET ou un BJT de puissance.

    Reply
    • admin says

      October 31, 2017 at 9:00 am

      Les triacis étant connectés à une alimentation en courant alternatif, ils ne verrouillent jamais, les triacs ne verrouillent que lorsque l’alimentation est en courant continu pur.

      Reply
  10. Colin Mitchell says

    September 8, 2017 at 1:58 pm

    This is wrong:
    According to the strength of the light it obtains, it possesses a resistance of 200 ohms at nighttime and during daylight a few thousand Ohms.

    Should be:

    According to the strength of the light it has a resistance of a few thousand Ohms at night and 500 ohms during daylight

    Reply
  11. Colin Mitchell says

    September 8, 2017 at 1:53 pm

    The resistance of the LDR will not go low enough to turn off the BT136

    Reply
    • admin says

      November 26, 2021 at 10:41 am

      It seems you have no knowledge of LDRs. The dark resistance of an LDR can be as high as 2 megohm and higher

      Reply
  12. Colin Mitchell says

    September 8, 2017 at 1:48 pm

    Have you worked out how much current will be passed by the 1u capacitor, through the LDR when it is illuminated?
    I expect the LDR to blow up.

    Reply
    • Colin Mitchell says

      September 8, 2017 at 1:51 pm

      Delete the above.

      The current will flow through the 1k and BT136

      Reply
    • admin says

      September 8, 2017 at 8:50 pm

      I got it from this website

      http://www.schemas-electroniques.tk/2016/01/schema-electrique-alimente-directement.html

      Reply

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