PCB Candle that glows forever- KINDA

Hey everyone how you doing!

So this is an EVER GLOWING CANDLE PCB that will glow forever and never run out of wax because it's not made out of wax.

However, it will stop glowing after a month of constant blinking when the battery runs out.

The Idea here was to make an awesome and safe night light-decorative light for my desk, Aroma candles, and other decorative candles look great but they are dangerous to keep around, the fire hazard is one of the problems that can cause because of Candles.

To Be honest, this small reason was enough to make an alternative with PCBs because that is what I like, making designs of different stuff from PCBs.

As for the circuit, I utilized a simple FLIP FLOP Circuit that utilizes a couple of BC547 NPN transistors with few resistors and SMD capacitors.

About the working of FLIP FLOP Circuit

This circuit is a FLIP-FLOP circuit that is designed around a BC547 NPN Transistor that is connected in such a way that the capacitor is connected to the base of the transistor and when it gets charged, the transistor provides a pulse for a short duration to the base of the transistor causes a blink. this process is the same for both LEDs and causes a FLIP-FLOP blinking effect.

Why not use a Microcontroller?

Intead of utilizing the above FLIP-FLOP Circuit, a microcontroller like ATTINY13A or STM8 could be used here as well which could make this setup a lot easier and its code would be much simpler.

The reason was to not rely on MCUs for such a simple task because of two reasons, first one is the global chip shortage which makes these mentioned MCUs hard to get and the second reason is the cost, ATTINY13 cost more than 2$ nowadays, and its lead time is also too long so instead I utilized an OLD but GREAT Method to flash two LEDs.

MATERIAL REQUIRED

Following are the materials used in this built-

• CUSTOM PCB
• LED 0805 Package ORANGE
• LED 0805 Package WHITE
• BC547 transistor SOT23-3 package
• 10K Resistor 0805 Package
• 100uF 16V SMD Capacitor
• CON2 Header pin, Male and female both
• CR2032 Coin cell and its SMD Holder
• Arduino Nano - for demonstration, you can use any DEV Board
• LEDs 3mm any color

ARDUINO SETUP

Here's an example of how we can make this same setup with a Microcontroller, An Arduino is being used here but instead of NANO, we can utilize ATTINY MCUs by using the same sketch with a little bit of PIN Number change.

As for wiring, two LEDs are connected to the D2 Pin of the Arduino and one is connected to the D3 of the Arduino.

Here's the code-

int pinsCount=2;                        // declaring the integer variable pinsCount
int pins[] = {2,3};          // declaring the array pins[]
void setup() {
pinMode(2, OUTPUT);
pinMode(3, OUTPUT);
}
void loop() {
for (int i=0; i<pinsCount; i=i+1){    // chasing right
digitalWrite(pins[i], HIGH);         // switching the LED at index i on
delay(70);                          // stopping the program for 100 milliseconds
digitalWrite(pins[i], LOW);          // switching the LED at index i off
}
for (int i=pinsCount-1; i>0; i=i-1){   // chasing left (except the outer leds)
digitalWrite(pins[i], HIGH);         // switching the LED at index i on
delay(70);                          // stopping the program for 100 milliseconds
digitalWrite(pins[i], LOW);          // switching the LED at index i off
}
}

PCB DESIGN

Because this board was themed around a candle, I first searched for a Black and white image of a candle on the internet, after converting the image format into BMP, I imported it into my PCB Cad software and save it as a Silkscreen Top layer.

I designed the schematic and then converted it into a board file.

After using the saved candle layout, I added transistors, resistors, and capacitors on the middle section and leds on the flame part.

White LEDs will be placed in the middle and orange LEDs will be placed on Top of the flame.

As for the LED placement, I added LED inverted so their glow will be visible from the front of the PCB.

For this, the soldermask of the TOP Layer is open in the whole flame section, this will let the glow of LED transfer from the Bottom side to the TOP side through the FR4 Board.

FR4 will act as a diffuser in this case.

GETTING PCBS FROM PCBWAY

After completing the PCB Design, I exported the Gerber data and send it to PCBWAY for samples.

I choose Yellow Soldermask for this project, Candles are white and I should've chosen a white mask but no worries, I will be ordering Version 2 of this project in a white color mask.

PCBs got delivered in a week which was super fast.

As for the quality of the PCBs, each PCB were made properly and there were no error or misprints anywhere.

Overall quality was super and I recommend you guys for checking them out if you need great PCB service for less cost.

Also, I designed the PCB in such a way that we can disconnect the Candle PCB with its Coin Cell Holder board by cutting a join in between them by a cutter.

After partitioning the PCB into two separate boards, we prepare for the assembly process.

PCB ASSEMBLY

PCB ASSEMBLY Process contains three major steps which are-

• Solder Paste Dispensing
• PICK and PLACE Process
• HOTPLATE REFLOW Process

SOLDER PASTE DISPENSING

The first step is to apply solder paste to each component pad. We use Regular Sn-Pb solder paste that has a melting temp of 140 to 270 °C.

PICK AND PLACE PROCESS

I then used an ESD Tweeaser to carefully pick and place each SMD component in its assigned place one by one which took like 30 Seconds tops but the result was a perfect PCB with all the components placed in their location.

LED PLACEMENT

As for the LED Placement, we add them inverted in their pads, because I'm using 0805 package LED and the Pad on PCB is 1206, it can easily hold the inverted LED, just make sure to apply extra solder paste to LED Pads.

HOTPLATE REFLOW PROCESS

After the "PICK & Place Process", I carefully lifted the whole circuit board and place it on my DIY SMT Hotplate which is also homemade just like this project.

After a few mins when the hotplate reaches the Solderpaste melting TEMP, all the components will get soldered by this Hot Reflow process.

BASE COIN CELL HOLDER PCB

• After completing the Candle PCB, we make the Coin cell Board by first adding solder paste to all three pads of the coin cell holder board.
• next, we place the SMD Coin Cell Holder in its assigned place and reflow the whole board.
• After reflow, we add the CON2 Female Header Pin on the board by using a soldering iron.

This board will be the main power source of the candle.

ADDING CON2 PORT

After the Hotplate reflow process, we check the Candle board visually and then add a Vertical CON2 Male header pin to the Candle board by using a soldering Iron.

This CON2 port will let us attach this PCB on a breadboard for power or on its Coin Cell board.

RESULT

Here's the result and as you can see, this setup is blinking and is working properly.

Version 2 will be much bigger and will feature more LEDs and possibly a much better Blinking circuit.

Till then, stay tuned. Special thanks to PCBWAY for supporting this project, do check them out for getting great PCB Service for less cost.

Peace out