Introduction: 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!
Supplies
Resistors (1K/1Ohm)
Axial Inductors (100uF)
NPN Transistor (BC337-25)
AA or AAA dead battery
For magnetic connectors:
Wires
Tools:
Step 1: The Circuit
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)
Step 2: Pcb
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.
Step 3: Tests and Components
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...
Step 4: Stand and Magnetic Connectors
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.
Step 5: Ciao Ciao Ciao
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