This project describes how to build a hand crank Lego usb charger with parts from a Mindstorms kit and Radio Shack.

The charger uses a Lego motor to generate current which is passed through a voltage regulator and then to the usb port.

It would make a great stocking stuffer for anyone who uses devices that charge via usb. If you are getting it for a person who likes to build their own things, just collect all the parts put them in a ziplock, and put that in the stocking. Then when they want to build it you can show them this instructable.

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Step 2: The electronics

The 3 parts needed for this step are:
- Short lego wire, cut the block piece off one end and strip about a centimeter of the wire off
- +5V Fixed-Voltage Regulator 7805
- Female usb port

Plug the lego wire onto the motor as shown in the photos, test out which wire is positive by connecting the stripped wires to a multimeter and cranking the motor. Wire the positive end to pin 1 (input) on the voltage regulator. Wire pin 3 (output) to pin 1 on the usb port (if staring into the socket while the contacts on the inside are facing down, pin one is the farthest to the left). Wire pin 4 on the usb socket, and pin 2 on the voltage regulator to the negative lego wire.

Step 3: Ad ons

It is easy to create devices (ex: flashlights) that can be plugged into the motor or the usb port to provide power. For this project I enabled collaboration, so if anyone has any ideas for ad ons let me know and you can put them in.
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Raptor Z2 years ago
in my opinion its not worth it, as the motor costs 20-30 dollars, and you can buy a small dynamo hand charger for 3 dollars.
Brickman4 years ago
do you know which side of the lego wire is positive and negative? O and Radioshack carries the 7805 voltage regulator, i got it pretty easily.
Since the motor can be turned either way, I think the polarity can change. The next question is would this still work if a tiny rectifier bridge was added - like this one - It would drop a few volts mind...
thats.... thats INGENIOUS!!!!!
harry884 years ago
its so simple yet so good i dont no what to rate him
Fingers01105 years ago
Couldn't u use another motor attached to the crank in order to charge something instead of standing there for an hour cranking? Would work just as well, instead of tiring your arm out =)
 Then what is the use?
Find a power source, convert it to movement and then convert it back to power?
All you're gonna do is lose power on the way (goes to heat by friction). 

I've seen projects on instructables to charge USB devices using normal batteries (AA, AAA, 9V). Might be a better solution if you don't want to do some effort for the power. 

This is a nice thing to have with you if you run out of power without any batteries or other power source nearby. 
farmall4 years ago
could this thing be used as a usb driven motor?
so i can control my legos?
TarzanJr5 years ago
no lol
Chromatica5 years ago
did this all come out of one set of legos
where do you get the lego engine? Ive never seen one that actualy puts out electricity
it's just an electromotor. Normally you put electricity in it and rotation comes out, but he uses it as rotation in -> electricity out
Tetranitrate (author)  Impendingdoom7 years ago
It is the standard lego motor that comes in all mindstorms kits.
merijnvw5 years ago
wsx5875 years ago
do you need a voltage regulator
Otaconmgs6 years ago
Where did you get the voltage regulator?
just search for voltage regulator 7805 and order it
mikemike7 years ago
the worst of it is trying to find the right piece of junk to get the +5 volt regulator....i don't have a radio shack round ere'....:(....but still beautiful idea and i love it :D
Every old computer power supply and most other digital electronics will have 7805 regulator in them.
Derin Antpopper5 years ago
And UPS's.Definitely those.
pballpro445 years ago
can i use a different voltage regulator
DemeGeek5 years ago
What Mindstrom kit did you use?
He used RCX parts.
i actually dissected a flashlight that uses the crank (not as remarkable, sure, but,) and soldered the same USB stick you showed to make a charger for my iPod.
leevonk7 years ago
cool, I wonder if the pulsing of the charge isn't bad for the battery though. I don't know why it would be, but not sure.. also, if you ever rotate the thing in the wrong direction, wouldn't that create an oposite polarity of voltage which would harm the 7805 regulator (and maybe the ipod) ?
I understand your concern, however the voltage regulator IC should regulate the power enough to prevent it creating a problem. regarding polarity, assuming the motor output was DC, a diode could be used to ensure that the battery only receives the correct polarity. however if you wanted to charge the battery regardless of the direction of the motor turning, you could add a full wave rectifier, this would have to be implemented before the regulator chip. the downside of this, is that due to the diodes a small amount of voltage would be lost. depending on the motor, a better gear ratio could be used to make up for this. as long as the ratio doesn't make turning the crank too difficult. cheers
oops I just posted a comment on the whole diode thing, then scrolled down and saw your comment :D
geeklord5 years ago
I might be wrong but i recommend putting a diode (1n4001 worked for me) on the negative output of the generator, just in case it is cranked backwards.
mcdonn1236 years ago
You could replace the usb port with a 12v plug (the ones inside people's houses). Then you could charge your lego 'smart brick' or even your psp!
to charge any device via usb you simply need a usb charger cable

they arent hard to find google shopping gave me this in a second or so for a psp
You would also have to crank really fast for about an hour and use a 12v, 7812 voltage regulator to charge a smart brick with rechargables.
someone mentioned that you need to filter the chopped up DC current in order to not harm the 7805. You could easily put a capacitor in there...
what no one realizes is without a built in battery you would have to constantly turn the crank to charge the device, and because many items take several hours to fully charge this would only be useful in emergency situations.
You could just have a friend crank it while you plugged in a cellphone or something.
casperdixie6 years ago
I made this with a 1/10 gear ratio, you barely have to crank to generate a more than 5v charge.
leet hacker6 years ago
for all you who are wondering where to get a motor, if you haven't yet, try they have just about every single lego brick and piece ever made.
crapflinger6 years ago
Tetranitrate (author)  crapflinger6 years ago
Cool, thanks for letting me know.
cspannos6 years ago
Ah, ebay to the rescue... Do you have a model number or a suggestion on to which one I should buy??

cspannos6 years ago
What an awesome project! Do you have the specs as far as voltage and current that this puts out? Also, where can I get that Lego motor? I searched for Mindstorms kits with no luck... Thanks!
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