Endless Light With Dead Batteries. Yes, It's Another Joule Thief!

I was looking for a simple circuit to try and make my first pcb on an online PCB prototype service.

I decided to make a joule thief because it's a simple circuit that intrigues me a lot. I also find it very useful for reusing old batteries.

In particular, I would like to analyze the response of the circuit by trying to assemble various components, to analyze their efficiency and functioning. In the future I would like to design a small flashlight that allows to use "dead batteries" with a good light output!

The construction of the circuit was very cheap. Less than two euros for pcb and components!

Credits to:

• Rustybolt.info, fantastic blog with lots of examples and documentation.
• Pcbway, which voluntarily sponsored the pcb of the project. Thanks for the support guys!

Pcb or prototype board

Resistors (1K/1Ohm)

Axial Inductors (100uF)

NPN Transistor (BC337-25)

5mm Led

AA or AAA dead battery

For magnetic connectors:

Wires

0.1x5mm Nickel Plated Strip 

n52 3x6mm magnets

Tools:

Soldering Iron

3d printer

Power supply

For those who don't know it, joule thief is a "minimalist self-oscillating voltage booster that is small, low-cost, and easy to build, typically used for driving small loads. [...] It can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead") [...] The circuit is a variant of the blocking oscillator that forms an unregulated voltage boost converter. [...]". (WIkipedia)

The web is full of examples, diagrams and documentation on this simple circuit!

I mainly took inspiration from the Rustybolt blog. In particular, the only small thing to say about my circuit is that I avoided using the ferrite core to make the circuit smaller and easier to build.

(Pictures from Google and wikipedia)

To design the pcb I used Kicad. It seems to me a very professional tool, totally free and open source!

I didn't take much time to make the schematic and circuit. The slightly longer part was to place the components symmetrically. I didn't have any major difficulties, as Kicad is very well documented and has a very active community.

As I anticipated, I made the pcb with Pcbway, who very kindly decided to sponsor my little project!

The cost of small productions is quite low. For 5 or 10 PCBs you can pay even less than one euro each.

The end result looks clean and professional...

You can download the gerber file from this link.

I attach the circuit in the pictures. It is very simple and you can make it even without the pcb.

Reading this article I decided to use 100uF inductors and BC337-25 transistors.

As you can see I used axial inductors because I'm lazy and didn't feel like making them by hand with cables and ferrite cores!

After trying various resistances, I made 2 identical boards in which only the resistance changes.

With the 1k resistor the circuit is able to turn on a led from 0.6 to 1.5v.

With the 1 Ohm resistance it is able to turn it on from 0.4v but, raising the voltage beyond 1.26v, the led turns off.

I don't think the circuit is very efficient but it is still useful for reusing batteries that should be thrown away and for educational purposes!

I will be posting photos and videos of the oscilloscope analysis soon...

Once the pcb was soldered and finished, I was afraid that all these boards would remain closed in the drawer, so to complete the project, I decided to make a 3d printed small stand and magnetic connectors. This way I could use it, for example, as a small night light in my house!

Find all the files on thingiverse or you can download them below.

At the end of the project, do you have any suggestions on how I can improve the circuit?

I realized I ordered too many pcbs... If you want, write me on ig and I'll give you one! I'll give you the pcb for free, but you pay the shipping costs :) I'm in Italy right now, so I think it's cheap to ship all over Europe... Unfortunately, if you're outside Europe, I think the shipping costs would be very high... In any case you can download the gerber from here.

Ciao ciao ciao

Seguitemi!