Instructables
Picture of Color Changing Night Joule Thief
I got this inquiry from a teacher who teaches high school kids electronics - can we have a cool kit like Aurora mini 18, in a simpler and more affordable format? I suggested Night Joule Thief, but the teacher felt that it wasn't sexy enough for the kids. (ur... you know what I mean.)

So I combined the multi-color LED and Joule Thief in one, and got Colour Night Joule Thief. It's a mood lamp version of Night Joule Thief.


 
 
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Step 1: Features

Here are the highlights of the Colour 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
    * A multicolor/color changing LED
    * Automatic turn on via a light sensor (adjustable sensitivity level)
    * Energy efficient - works even with a run-down battery, down to 0.6V
    * Makes a great little mood light
ledartist (author) 1 year ago
This popular kit is now available at The Maker Shed!

http://www.makershed.com/Color_Night_Joule_Thief_p/mkla1.htm

Thanks!


raydar670 made it!2 months ago

I recently bought the kit from MakerShed and assembled it, but I found that a partially dead AA battery wasn't enough to power it (it's about 1.34V). I checked the voltage drop across the LED and it was only about 0.85V which wasn't enough to power the LED. I then decided to use my Arduino as a power supply and hook up 3.3V to the Joule Thief. It does light up, but the voltage drop across the LED was about 2.5V. So instead of boosting the voltage the circuit is lowering it. If I were to guess I think something is wrong with the capacitor or inductor. Is it possible I place the inductor in backwards reversing the polarity and changing the value? Also according to the parts list it's a 100uH inductor while this instructible states it needs a 470uH inductor. Not sure if that helps, but I'd love to get this working. Thanks!

IMG_20140712_184822.jpgIMG_20140712_184828.jpgIMG_20140712_184831.jpgIMG_20140712_184836.jpgIMG_20140712_184847.jpgIMG_20140712_184953.jpg

I got it working! I made a simple mistake of soldering one of the resistors in the wrong place. Once that was fixed it works fine with just an AA battery. The reason it still worked with straight 3.3V was because the way I had the circuit set up all the intermediate circuitry between the LED and the battery were bypassed so I was powering the LED directly with no boosting involved.

ledartist (author)  raydar6704 days ago
Glad to hear that you got it working. Sorry I could not respond sooner.
Regarding the inductor value - there's no performance change between 100 and 470 uH. Although in theory 100 uH should perform a tad bit better, due to it's lower DC resistance.
Also, inductor polarity doesn't matter with this circuit (in most circuit it doesn't. It usually only matter when you have multiple inductors nearby.)

Thanks for the reply! And just one more update (because I can't seem to edit my previous post). I had switched one of the transistors with another one, so there was no switching going on at all (it wasn't a resistor that was the issue). That's why it would work at 3.3V and not the ~1V. Also, thanks for the clarification on the inductors.

ledartist (author)  raydar6704 days ago

I suspect that transistor got damaged, possibly by having a wrong resistor and applying higher voltage. It's never a good idea to apply higher voltage than the circuit is designed for, _especially_ when something is not working.

JonathanC21 month ago

so uh.. how long will this battery power the led?

pocokk2 months ago

Thanks for the pulsed DC voltage hints. I was stuck at only Red Color using slow flashing RGB LED. Now I know why and problem solved. I hereby salute you smart guy ! haha. Thanks Pal.

Robert Powell3 months ago
You are so helpful! I don't want to buy it so i did this, I already had a joule thief on my breadboard but my 3 pin color changing led wouldn't work cuz the fast switching so I put a shotky diode and a 100 uf cap and it works so good! Thanks!
Robert Powell3 months ago
You are so helpful! I don't want to buy it so i did this, I already had a joule thief on my breadboard but my 3 pin color changing led wouldn't work cuz the fast switching so I put a shotky diode and a 100 uf cap and it works so good! Thanks!
TxFireRanger8 months ago

Anyone know the value of the LDR? And which ones will work?

coloquei esse circuito na minha pipa hehehe vlw pela ajuda ñ saibia qual usava
jayz019821 year ago
do you have branch here in the philippines? so that i can order it here
ledartist (author)  jayz019821 year ago
Hello!

I don't have a branch or reseller in Philippines, but I ship there. Please go to www.theledart.com, and shop.

Thanks,
Aki
lgore932 years ago
Do you think I could maybe replace the PCB with a couple of popsicle sticks glued together? I know that sounds kind of ghetto, but I'm looking for a very inexpensive project to do in class. It would be much cheaper if I could make a working model on popsicle sticks. I know it wouldn't look as professional, but things would be much easier.
ledartist (author)  lgore932 years ago
Yeah, you should definitely try that. Please post the result!

Aki
Okay thanks! One more question which is probably obvious... The smallest photoresistor I can buy from the site I usually order from is 5k-0.5M ohm. Would the circuit work with this difference? I realize 2k ohms is a significant amount, but is it really that much on this scale? I admit that I know much less of electronics than I would like to, but I love learning and building new things. Thanks for your help.
ledartist (author)  lgore932 years ago
That will probably work. I'd just try it, maybe on a breadboard.

Aki
My parts came in yesterday, and I built it. It's not the prettiest thing in the world, but it works very well! I decided to use a piece of cardboard instead of popsicle sticks since it allowed for some less than... perfect wiring. Also, I found out I was out of electrical tape so I had to substitute duct tape in. Haha
IMG_0323.JPGIMG_0324.JPG
i was prepared to electromagnet 9v battery how much turns required 24 gauge wire
Mechiver electronics! Woot!
ledartist (author)  lgore932 years ago
Umm... You are good.
Nano_Burger2 years ago
LED Artist,

Can you use different voltage batteries with this circuit? O have 3v, 6v and even 12v photo batteries I'd like to drain off as well. They are probably not up to those voltages since they became too weak for their particular device so a few volts short.
ledartist (author)  Nano_Burger2 years ago
If the voltage is below 1.6V or so, then it's safe to connect to this circuit.

ciliar2 years ago
Aki, you are a star - soon to put Colour Joule Theif into action! Keep you posted!
ledartist (author)  ciliar2 years ago
Thanks!
Yes keep me posted.

Aki
markallie2 years ago
In the pdf version of the schematic an MPSA05 is listed as a choice for the PNP transistor, Q1. It is an NPN transistor.
ledartist (author)  markallie2 years ago
Thank you for pointing this out. I've corrected the error.

Aki
GASSYPOOTS2 years ago
how bout a self charging/ no batterys needed after 1st charge
unfortunatly, I don't think thats realistically possible. the reason for that is that it is going to lose energy no matter what. if it were 100% efficient, it would be possible, but it's not.
sageserver2 years ago
Can another LED be used in place of D1? or is the voltage difference too much? Very instructive instructable.
ledartist (author)  sageserver2 years ago
D1 is there to rectify the voltage, so it has to be regular diode. LEDs have too high of forward voltage drop.
If you wan to drive two LEDs, you can simply add another LED in series to D2. The brightness will go down a bit, but it will still work.

Aki