Picture of Joule Thief LED Night Light

I have many used batteries around. Remote controls, cameras, many electronic gadgets all use batteries, mostly AA size. I always felt guilty for throwing away the used batteries. I know there are rechargeable batteries, but many electronics don't work well with rechargeables.

I also know that those "used" or "spent" batteries usually have some juice left in them. So to come up with a good use of used batteries, I've created a LED night light.

I like having a little night light on when I sleep. LEDs are perfect for this purpose, because they are energy efficient, and good at providing low intensity illumination.

This LED night light operates with just one battery. It utilizes a little circuit called Joule Thief to boost voltage out of an AA battery. I also added a light sensor to turn it on automatically when the surrounding is dark.

The circuit is energy efficient, and requires very low voltage to work. So it effectively sucks every bit of energy out of batteries. This type of circuit is often called "Joule Thief", because it works as though stealing every bit of energy (Joule is a unit for energy) out of battery.

I'm calling this project Night Joule Thief.

*The kit purchasing info can be found herehttp://www.theledart.com/blog/night-joule-thief

Step 1: Features

Here are the highlights of the Night Joule Thief.
  • Compact & streamlined design
  • Uses only one AA battery (or any 1.5V battery you can hook up to)
  • Easily adaptable to different size batteries - hook up holes to attach home made clips
  • Two white LEDs
  • Automatic turn on via a light sensor (adjustable sensitivity level)
  • Energy efficient - works even with a run-down battery, down to 0.6V
  • Choice of through-hole only components or SMD - mix & match on the same PCB

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When the led lights up, it doesn't affect the light sensor?

ledartist (author)  Implicate_Order2 months ago

Not under normal use - those clear LEDs project light forward, so the light doesn't hit the light sensor. But if you have a reflective object near by, you can see the LEDs dim as their light hits the sensor.

MichelleO52 months ago
Does it have a block diagram?
elicitone made it!1 year ago

I bought the kite and it was shipped wicked fast... Took me about 30 mins to assemble it and it worked right off the bat. I put a 'Dead' battery that I pulled out of the garbage (it was in my cordless mouse) and it powered it over night and is still going just as bright.

Now i am going to try building one from scratch.

Thanks again... This one will go in a custom etched Sun Jar for my Girlfrind !!!

ledartist (author)  elicitone1 year ago
Great to hear the success story! It's amazing how much juice those "dead" batteries still have.
The PDF should be printed on what size of paper? Letter or A4? Does it matter?
ñ deu certo aki eu coloquei um bc548 entre o negativo e liguei no capacitor cerâmico, o LDR coloquei na base e liguei no resistor de 1k

Essse circuito e tão leve que eu coloquei na minha pipa com uma pilha recarregável voou de boa vlw pelo circuito
manuka4 years ago
Very neatly done! However perhaps instead consider hacking a solar garden lamp ? Most of these now use a 4 lead "quadistor" that'll simplify your circuitry!
ledartist (author)  manuka3 years ago
I'm aware of that IC, but can't find anywhere to purchase. (except taking it out of a garden light) Do you have a source?

Also, that IC won't work with this project because it uses the solar panel as a light sensor...

Simply source them from cheap Solar Garden Lamps ! These things are a parts goldmine anyway- for ~$2 you get a PV,NiMH/NiCd cell, a switch,battery holder,inductor & the "quadistor" circuitry!
I bought a few of these, only to find that the IC is a SMD, potted onto the board. Drat. There are 8 traces that run under the potting glob, so no clear answers. There are only 3 resistors and two caps, no Schottky and no inductor.

I think I"ll buy a kit from ledartist!
Just grab ZE002 from a solar garden lamp -for just a few $ these lamps are a parts goldmine !
duggerpato2 years ago
Hey, I'm noticing the inductor has a much longer lead on one side. Does this mean I need to worry about its orientation on the board? I'm probably just being overly cautious, but want to make sure.
ledartist (author)  duggerpato2 years ago
Inductor orientation doesn't matter for this circuit.

fejfish2 years ago
You can buy something that does the same thing for less than £1 with the added advantage that it contains a solar panel to recharge the included NiCd or NiMH cell during daylight. It,s called a solar garden light!
ledartist (author)  fejfish2 years ago
It is amazing what a mass production can do... However where's fun in just buying things? Building things with your own hands and learning from the process - isn't that the DYI spirit?
I've read where there are a few people that seemed to be highly focused on a narrow definition of Joule Thief. But isn't the main focus here intended to be on electronics rather than grammar or semantics? Besides, the meanings of names often change over time. Like, "I'm using a mouse to operate my computer even though we don't live with mice and I'm not really computing anything. Surely using these words this way isn't seriously confusing or worth fussing over. If something acts almost exactly like a "Joule Thief," why default to a more general term like Voltage Converter, etc...

Not only that, I'm rather biased with by the work of ledartist since I successfully used part of his circuit (diode and cap) to get my particular IC and inductor only "Joule Thief" to work with a flashing, multicoloured LED. Otherwise, I wasn't able to get this flashing LED to work with my circuit - see "Joule Thief" circuits, crude to modern...
ledartist (author)  acmefixer4 years ago
I know the original circuit only uses one transistor, but the two conductor inductor is harder/expensive to purchase, and winding own inductors is a bit of work. I think using one extra transistor is a good trade off for not having to wind an inductor by hand. It also makes economical sense. (transistors are very cheap, so are single coil inductors.)

I did mention that my version is a _variation_ of original, which I find very often on the net. I also think that showing different ways to achieve the same result can be inspirational.

I also contacted the person who named the circuit "Joule Thief" (Big Clive) and he did not have a problem with me using the name.


ledartist (author)  acmefixer3 years ago

I'm sure it's easy for people who already has wire, etc. in hands, to make their own inductor. However even I (who tinker with electronics all my life) find purchasing the wire, and winding the coil to be cumbersome. So the reality is that most people will find it to be too much work.

Those who don't mind winding their own inductors most likely have already made their own Jule Thief.

I'm trying to get the widest audience to be interested in this (variation of) Joule Thief, so I designed the circuit to be as fool proof as possible.

Having said all that, I really think you should post your Joule Thief on Instructables. There are many people who want to know exactly how the circuit works, how to make the best inductor, etc.

Acme, I encourage you to fix the Wiki for JT then. If you have the knowledge needed for the task, and the time of course, then you should go ahead and fix the wiki. That's what make Wikipedia work, having the world maintain the global knowledge base. Thanks for letting us know that the information is not correct.
colin553 years ago
Here's a Joule Thief with 10 LEDs on a 9v battery:

The inductor is simply a nut and bolt. It works just as efficiently as a ferrite core and it's easy to find.
Good day, can you please give illustration on how to wind the wires on the bolt and in which part did you joined the wire to make it out of phase. I would like to make one like this from above pictures. Thank you so much.
Today I put together the first of the kits that I bought. For an electronics newbie like myself identifying each pert with a picture would have made life easier. Anyway, I managed to use the photos in the instructable to get it right. The thing does not work for me though. I have checked everything twice and still nothing. I even wrapped the battery in paper in case it's housing was shortening out the circuit. Still nothing. My only thought is that part L1 (470uH) is polarity sensitive. One pin was shorter than the other but there was nothing in the instructions to indicate that it should go in a certain way. Before I start desoldering can you tell me if this is likely to be the cause.

Thanks, Wayne.
I feel so foolish - the problem was not the circuit but the power supply. 3 out of 3 batteries that I tried it with were all dead flat. It is all sorted now. Hooray!
ledartist (author)  waynevanwijk3 years ago
Ha! Congrats anyway!

ledartist (author)  waynevanwijk3 years ago
Hello Wayne,

Inductors don't have polarity par-se, but they indicate the polarity in terms of magnetic field. Only matters when you have two or more inductors sitting close together.
So if your unit is not working, please check other things, such as;
- polarity of LEDs
- correct transistors - Q1 and Q2/3 are different
- resistor values
- quality of solder joints (open or short to adjacent pads).

Did you look at this i'ble? http://www.instructables.com/id/Joule-Thief-LED-Night-Light-Kit-Step-by-Step/

Lastly, make sure to test your unit in a very dark place. Also test with the trimmer turn to the both extremes.

Good luck,
Tinkerteem3 years ago
pongpak3 years ago
Is ti possible to bypass the CdS cell and Potentiometer with a switch. Would I have to change the resistance of R3
ledartist (author)  pongpak3 years ago
That's pretty simple. Just leave the CdS out, and put a switch where the pot was. See the PCB image with note.
No need to change R3.

or is there any possibility that i can buy your circuit board here in the Philippines? have you distributed already your circuit board in the market? please help me get one of it. thanks a lot.
ledartist (author)  rainbowrider423 years ago


Yes you can purchase the PCBs. Please see the pricing/details here:
hello. My name Is MJ Laurel. Actually I am from the Philippines. I m an avid fun of DIY projects at instructables. but I am fascinated more with your bright idea of using used batteries through your Joules circuit, I would like to know how much is the cost of your Joules circuit board. I really want to assemble one but I do need a circuit board. I got a little knowledge about electronics but i know how to read the instructions and the circuitry. Is it possible for me to get one of your circuit board? how much it will cost for me? I do hope you will reply me. thank you so much for this very bright idea.
ledartist (author)  ledartist3 years ago
You can also leave out Q1 and put a switch between battery positive and R1.
jimengn013 years ago
I think this is a great idea, I have a project I am working on and need someone to help me design a prototype PCB board. I am willing to pay once the non discloser and non competes are signed....... Great job !!
ledartist (author)  jimengn013 years ago

Sounds good. Let me know when you are ready!

Aki, I am ready, I am new to this forum, we need to be able to communicate outside this forum, how do you suggest we do that, are we able to exchange data here ??
ledartist (author)  jimengn013 years ago
I will PM you.
lol now i feel dumb ! PM ??
ledartist (author)  jimengn013 years ago

You can send personal message via profile page. I already sent you one, so you will get it.

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