• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

  • 1000+ Circuits
  • Privacy Policy
  • About Us
  • Contact
  • Disclaimer
  • Videos – Circuit Test Results
You are here: Home / DIY LED Projects / Automatic LED Candle Light Circuit

Automatic LED Candle Light Circuit

Last Updated on March 13, 2019 by Swagatam 16 Comments

The post describes a simple 220V  mains transformerless LED candle light circuit which switches ON automatically in the absence of ambient light in the room and vice versa. The idea was requested by Mr. Don

Technical Specifications

I only dabble with electronics here and there but in trying to move from incandescent and CFL's to LED's I have come across a strange dilemma.   I have used electric 110v-120v "Sensor Candles" for many years and they employ a very simple circuit of an LDR/Resistor/Switching Transistor on a circuit board about 1/2" square that fits into the body of the candle.

The candles (not flickering) use c7 5-7 watt incandescent bulbs.  The equal c7 LED of about .5 watts do not work in these candles.  What is it about the LED bulbs that causes them not to work?   Is there a modification that can be done to the existing circuit boards to make them compatible with LED's?   I have searched all over for electric candles that use LED's and can find none.  The LED candles that are available are only battery operated.  It boggles my very old and simple mind that the switching transistor does not simply switch the necessary voltage to the LED.

I find it hard to understand why these products have not been produced to function with LED's.  Perhaps this is a product to might want to design for manufacturers.   I have one grandchild who has a degree in electrical and computer engineering that promised to review the possibilities but other his other priorities have taken precedence, even though I told him that a patent on the idea might be rewarding.

I can send you a candle, circuit board, or whatever information you may require.

Thanks,
Don Jengo

The Design

The proposed automatic darkness triggered candle light circuit can be seen in the shown diagram which uses an amber colored LED for simulating a candle light effect.

As per the request the circuit needs to be LDR based which also means the unit must activate only when it's sufficiently dark inside the room or as soon as the main indoor lights are switched OFF, or when the user goes to bed.

The presented automatic LED candle light is very straightforward and fairly reliable with its operations, let's understand it through the following explanation:

The 0.33uF/400 V capacitor along with the four diodes and capacitor forms a compact transformerless power supply circuit stage for powering the LED during dark or in the absence of ambient light.

The first transistor from left in the presence of ambient light conditions receives sufficient base drive via the LDRs lower resistance and conducts to keep the base of the second BC547 at ground potentials.

Due to this the second transistor remains inactive and switched OFF making sure that the connected LED also remains switched OFF under such ambient external illuminations.

However as soon as the ambient light around the LDR diminishes or is switched OFF, the left transistor is inhibited from the base drive due to the LDRs high resistance in the absence of ambient light, which further prompts the right hand side transistor to start conducting, thereby switching ON the LED.

The opposite reaction is quickly exhibited in case the ambient light is switched ON or during daybreak.

Caution: The circuit is not isolated from mains voltage, utmost care and precaution is expected from the user wile assembling, testing, installing the unit in powered situation.

The LDR must be appropriately enclosed inside a suitable cover such that the LED light never reaches it under any condition, otherwise it may lead to false triggering and oscillations of the circuit and the LED.




Previous: LED Brightness and Efficiency Tester Circuit
Next: Wireless Helmet Mounted Brake Light Circuit

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

You'll also like:

  • 1.  0.6V to 6V/12V Boost Converter Circuit
  • 2.  3 Watt, 5 Watt LED DC to DC Constant Current Driver Circuit
  • 3.  110V Compact LED Tubelight Circuit
  • 4.  Sunrise Sunset Simulator LED Circuit
  • 5.  LED Driver Power Supply Circuit Using Dimmer Switch
  • 6.  LED Obstruction Light Circuit

Please Subscribe (Only if you are Genuinely Interested in our Newsletters)


 

Reader Interactions

Comments

    Your Comments are too Valuable! But please see that they are related to the above article, and are not off-topic! Cancel reply

    Your email address will not be published. Required fields are marked *

  1. Search Related Posts for Commenting

  2. gurucharan gupta says

    Sir I have 12v 8ah battery and 12v dc led bulb and I want to add LDR function please help me with circuit

    Reply
    • Swagatam says

      Gurucharn, you can try one of these concepts:

      https://www.homemade-circuits.com/how-to-make-light-activated-day-night/

      Reply
  3. Nelio Abreu says

    Hi Swag,
    What’s the minimum voltage I can apply to this circuit?
    NA

    Reply
    • Swagatam says

      Hi Nelio,

      you can use 12V DC without the capacitor. With the capacitor the minimum input should be above 25V AC.

      Reply
  4. Swagatam says

    yes can be used

    Reply
  5. basit momin says

    Sir can I use 9v battery for this circuit

    Reply
  6. basit momin says

    And is their any value for LDR sir

    Reply
    • Swagatam says

      a good recommended LdR will normally have a resistance value between 10K to 100K in room light and over 3M in darkness….you can check this while buying with a ohm meter

      Reply
  7. basit momin says

    Sir can I use 12 v battery for this circuit

    Reply
    • Swagatam says

      yes 12V battery or adapter can be used

      Reply
  8. Noor rahman aziz says

    Dear sir Can I use the 12v relay

    Reply
    • Swagatam says

      yes can be used, but will need to make 0.33uF into 1uF

      Reply
  9. adio kabiru says

    what is the wattage of the led use and the color

    Reply
    • Swagatam says

      3.3 v, 20 ma, amber or yelllow

      Reply
  10. Chiranjit Samanta says

    Dear sir in my area I can't found 0.33uf/400v & 100uf/50v. If its possible with a few changes please help me out.. I'm very interested about your site. Thank you.

    Reply
    • Swagatam says

      Chiranjit, you can try other closer values between 0.22uF/400V to 0.47uF/400V

      same for 100uF/50V…. use any close value, it's not critical

      Reply


  11. COMMENT BOX IS MOVED AT THE TOP


Primary Sidebar

Electronic Projects Categories

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (51)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (92)
  • 741 IC Circuits (18)
  • Amplifiers (49)
  • Arduino Engineering Projects (82)
  • Audio Projects (84)
  • Battery Chargers (75)
  • Car and Motorcycle (87)
  • Datasheets (45)
  • Decorative Lighting (Diwali, Christmas) (31)
  • DIY LED Projects (81)
  • Electronic Components (97)
  • Electronic Devices and Circuit Theory (35)
  • Electronics Tutorial (99)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Games (2)
  • GSM Projects (9)
  • Health Related (17)
  • Heater Controllers (23)
  • Home Electrical Circuits (98)
  • Incubator Related (6)
  • Industrial Electronics (26)
  • Infrared (IR) (39)
  • Inverter Circuits (94)
  • Laser Projects (10)
  • LM317/LM338 (21)
  • LM3915 IC (24)
  • Meters and Testers (54)
  • Mini Projects (153)
  • Motor Controller (64)
  • MPPT (7)
  • Oscillator Circuits (12)
  • PIR (Passive Infrared) (8)
  • Power Electronics (33)
  • Power Supply Circuits (66)
  • Radio Circuits (9)
  • Remote Control (46)
  • Security and Alarm (56)
  • Sensors and Detectors (115)
  • SG3525 IC (5)
  • Simple Circuits (72)
  • SMPS (30)
  • Solar Controllers (60)
  • Timer and Delay Relay (51)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (38)
  • Ultrasonic Projects (12)
  • Water Level Controller (45)

Follow Homemade Circuits

Facebook
Twitter
YouTube
Instagram
My Facebook-Page
Quora

Feeds

Post RSS
Comment RSS

Circuit Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2021 · Swagatam Innovations