Christmas Decorations Using Flickering LED Candles

About: I am a researcher working on development of optical atomic clocks. Electronics is my hobby since childhood when my uncle was bringing me old phones to play and take apart.

Ever fascinated a candle light?

For the last decade LEDs have been made that flicker similarly to a candle. They contain a digital chip and can be driven from a 3V lithium cell. So far I haven't seen a 7 candle Christmas decoration using the flickering LEDs. The result was very nice.

To make such a thing you need to replace 7 incandescent bulbs with yellow flickering-candle-LEDS. Hot-melt glue was used to fix things. LEDS can not be driven by 5V!

A miniature 3.3V power supply board was placed inside the wooden mount:

https://www.ebay.com/itm/AC-220V-to-DC-3-3V-1A-3-3...

Step 1: Advent Wreath With 4 LED Candles

There is a nice christian tradition to start to prepare 4 weeks before the Christmas for the birth of Jesus. A popular decoration is an Advent wreath with 4 candles were one additional candle is lit every Advent sunday. To make it you need to decorate a wreath with 4 flickering LED candles. They are safe to use in respect of fire hazard.

Step 2: Candle LED With a Large Capacity LiPo Battery.

Replacing the small 3V Li cell with a 4V LiPo pack allows to extend the light from ca 10 hours to a month. A 100 ohm resistor should be used to drop the voltage better in series with a diode providing 0.6V voltage drop).

Electronic candles become popularl for grveveyard too.

https://www.ebay.com/itm/Cross-LED-Electric-Candle...

Step 3:

2018 Christmas time comes with tiny SMD leds soldered in parallel to two thin wires and protected by a drop of transparent glue. LED chain is so lightweight that can be raised into the air by a helium balloon. Typically 30-40 LEDS separated by 10 cm are driven by a control chip and powered by two AA batteries.

After the helium leaks out, the LEDs can be fixed to a plastic ball hanged from the window-top. Hot air from room heating moves it around slightly. Power can be supplied by 0.2 mm diameter enameled wires. A 0.35 mm nylon fishing line can be used to strengthen the suspension. AA batteries keep the thing running for a couple of days and can be later replaced by a a 3.3V board driven by a 5V USB charger.

A disadvantage of driving different color LEDs in parallel is that different colors appeared in different brightness.

To circumvent the brightness issue I used Arduino. A single PWM output (pin3) was enough to drive the 30 LED brightly. (To increase the current several PWM outputs of the Arduino could be soldered in parallel).
Now you can play and make your own light effects. Below is an example for slowly changing brightness:

void setup() {Serial.begin(9600); }

void loop() {

for (int i = 0; i<100; i=i+1) {analogWrite(3,i); Serial.println(i, DEC); delay(1000);}

for (int i = 100; i>0; i=i-1) {analogWrite(3,i); Serial.println(i, DEC); delay(1000);}

}

Step 4: Flickering LED Simulator With Arduino

One could record flickering from a real candle using a photodiode or photoresistor on oscilloscope or Arduino with 25 samples/second and later play back the sequence on a regular LED.
This could be an idea for some school level research project.

Arduino whith a photosensor also allows to implement automatic switching on during darkness.

Good luck!

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