3D Printed "Floating Candles" Powered with Joule Thief

Floating Candles 

Harry Potter Style

The last few years I have begun to make home made presents for my family. Mainly small boxes made from wood, but more recently also 3D printed objects. 

I know that only children are supposed to make home made gifts. Though I'm quite grown up now - my sole is still a big child, so I allow my self to continue making home made gifts.

I needed a Christmas present for my sister in law and was a little lost for ideas. I also wanted my sister in law to get a home made present but as mentioned I didn't really have a good idea. 

Fortunately one of my favourite You Tubers (Big Clive) made a video about some floating candles.

See his video about Floating Candles here.

When I watch the video I thought that it could become a nice little project to make my self - and at the same time I had a Christmas present idea for my sister in law.

The 3D print

I create most of my 3D models in a the free program OpenScad. In OpenScad you don't draw your objects directly, you build them from simple objects as spheres, cylinders and cubes. It a little bit like programming your objects.

When designing the 3D model I initially had great difficulties figuring out how the switch the candle on and off. Also making it easy to replace the battery was a bit of a challenge. Even connecting the battery caused me some headache. After quite a few trail and errors I came up with a "screw to turn on and off" design. I split the candle in two halves with a thread.

That way I solved two problems in one go.

The switch is mounted at the end of the circuit board and gets turned on by screwing the candle tight.

To switch the candle off, turn the candle 'open' a couple of turns. In this way I could avoid having the switch visible. To replace the battery simply screw the candle fully apart.

Initially I wanted to print the flame my self, but the result was a little sad looking. As I had bought a bunch of LED Tea candles, for experimenting already, I decided to use the frame from them. The only modification I needed was to make a small hole for the hanging wire. The flame even had mounting tags so it not only simplified my 3D design, it worked perfect.

The circuit

I wanted the candle to be powered by a single 1.5V battery (AA/Penlight). I also wanted the circuit to be simple and not using any special components. 

The Candle LED I'm using requires 3.2 Volt to work so getting the LED to work from a 1.5V battery required some sort of 'step up' circuit. There exists countless ways to step up a voltage. They often require some special IC or chip to get working.

As I was a little in a hurry to get my project ready before Christmas, ordering components from China was not really an option. Furthermore, when ordering components from China, you don't always get what you ordered and the quality can be questionable.

So I wanted a circuit I could build from of the shelf components. I again turned to Big Clive. He has a great video about a small simple circuit called a Joule Thief.

See his relaxed How to make a Joule Thief video here.

Where normal battery operated equipment, such as your remote control, stops working when the battery voltage drops below 1.0 - 1.2 Volts, the Joule Thief will 'suck' energy out of the battery to as low as 0.6 - 0.7 Volts. So when the batteries in remote control gives up - you can use them in a Joule Thief and get quite a few extra hours out of them.

The basic version of the Joule Thief only requires a very few, of the shelf, components.

A general purpose transistor T1, a current limiting resistor R1, a small hand wound transformer TR1 and of course a LED. As I'm using a Candle LED I have added a few components - a diode D1 and a smoothing capacitor C1. In the design I also added a 3.2V Zener diode D2, but it turned out that it is not needed.

To prolonge the battery life even further I have added an extra current limiting resistor for the LED (Not shown in the circuit below.)

The modified Joule Thief

To make the circuit board as compact as possible I decided to use SMD (Surface Mount Device) components. Though they can quite difficult to work with, specially when ones eye sight start to diminish, it is very satisfying to see the end result. The issue I had connecting the battery to the circuit board  (I initially wanted to use an of the shelf battery holder) I solved by using battery clips I could mount on the circuit board.

Fully assembled circuit board.

As mentioned earlier, I had to get my components quite fast, so I ordered my components by Conrad. Generally the quality is alright, but also quite a bit more expensive than China.

When searching for Candle LEDs, I only found one type. The review for the LEDs was not great. They should be a little "too wild". I decided to buy a small amount anyway, just to check my self. 

The only alternative I could find was ready made Candle LED Tea candles. So I ordered a bunch of those too. Conrad tried to convince me to buy batteries too, but I was only interested in the LED so I didn't bother to order any batteries. When the order came through a fe days later, it turned out that the candles was delivered wit batteries. I can probably use a couple in my kitchen scales.

When comparing the two LED types, the of the shelf version flickers quite a bit. Something like a candle in a window-seal. The ready made version is much more quiet, barely any flicker. I guess it's a matter of taste, but I prefer the ones with more flicker.

The off the shelf LED does seem to dim faster as the battery wears out. I still need to test this better though.