Now you can have a regulated power supply constantly at your fingertips with NO batteries to replace or recharge! This Instructable shows you how to modify a keychain dynamo flashlight into a lean mean supply that can replace batteries for any projects requiring quick 5 volt direct-current (5V DC) power.

If you've even included digital logic, analog chips, or a microcontroller into a project there's a good chance you've had to find a way to provide 5V DC to your circuit. There are few primary sources of 5V, so you can use a wall wart to convert AC power (which obviously limits where you can take your new gadget) or you can spend extra time building a regulator circuit to get multiple 1.5V batteries to the needed voltage. These solutions are required for some circuits, but for smaller gadgets, wouldn't it be nice to have an always-ready supply so you can go straight to working on other aspects of the project?

By adding a few electronic components to a widely available dynamo flashlight, you can power small devices for short periods without using up outlets or batteries. The improved dynamo is great for the workbench or showing off new projects just about anywhere.

This Instructable covers how to assemble and install a step-up DC-DC converter that turns the varying low voltage of the keychain dynamo's generator into a constant 5V. The step-up circuit charges a large capacitor which provides energy storage and some power even when the dynamo isn't turning.

By following the steps in this Instructable, you can accomplish all this without manufacturing a special circuit board or using hard-to-solder surface mount components. To get the electronic parts inside the keychain case requires some circuit origami, but after about an hour of tinkering you will have a neat device that can source up to 50 milliamps of current at a constant 5V DC while winding and milliwatts of power for minutes after!

Step 1: How it works

Electric generator
Current flowing into a motor creates a magnetic field in coils attached to the shaft, which turns in the presence of a magnetic field from fixed magnets. When a motor is run in reverse -- power is applied by turning the shaft -- a voltage is induced in the coil. Faraday's law says this voltage is proportional to the rate the magnetic field changes in the coil. Thus the faster the shaft is turned, the greater the voltage.

Gear ratios
A series of gears are used within the keychain to get the generator spinning as fast as possible. When you crank the handle, it sets three compound spur gears in motion. One half of each compound gear has a small radius and the other half has a large radius. When the small radius is turned, the teeth at the edge of the larger radius change location at a proportionally faster rate. By cascading these compound gears, the cranking rate can be multiplied several times and the generator shaft can be turned much faster than a human could turn it.

The need for the step-up converter and storage capacitor
The keychain's gear ratio can generate a few volts with reasonable cranking, but the voltage is not high enough to reach 5V. This voltage also varies quickly based on the shaft rotation rate. To get a steady 5V output, a step-up converter is needed. The specific integrated circuit chosen -- the MAX756 -- can turn voltages as low as 0.7V into 5V and comes in a handy 8 pin package. The step-up circuit is based on the application circuit in the MAX756 datasheet.


Even though these dynamo keychain flashlights are advertised as needing no batteries, they appear to have three coin-sized batteries inside. The generator is soldered to this coin battery stack in a somewhat crude charging circuit. However, I do not think these batteries are meant to be rechargeable, and they tend to drain quickly after the initial discharge. This Instructable replaces this coin stack with a large capacitor that can be recharged more frequently and is more efficient.

See the schematic for the layout of the entire circuit. The specific components were chosen for easy hand soldering while being the smallest sizes that were still rated for the voltages in the circuit. Note: The MAX756 datasheet has C3 as a 150 uF capacitor. The 150 uF capacitors I found were much physically bigger than the 100 uF ones and wouldn't fit within the small keychain. Thus I replaced C3 with a 100 uF capacitor and it appears to work fine.
<p>I like the idea but I am going to incease the size of the leds and as you fit a super capacitor to see what happens hopefully I should be able to get 10min of light </p>
Since I'm trying to create this Joule thief supply with no dynamo flashlight, I'd like to know the reference for the diode D1.
Very detailed tut, just what i was looking for, got a few of these from DX with the intent to make a hand cranked arduino project, and your sweet little circuit origami is just what i needed to give these babys a little extra kick :) im actually thinking of custom casing with 2 generators on 1 crank, and (if i manage to tweak the components and still get it to work) will prolly try rebuild your circuit with a bigger capacitator that can deliver more mA. <br> <br>I want there to be enough power for some cool things, was thinking of a small rgb pixel matrix and some buttons and joysticks to make a hand cranked little handheld game :D though its kinda far fetched looking at the needed power and what can be achieved with these hand crank units, even when beefed out with your circuit. <br> <br>Either way, thanks for the great ideas &amp; details! <br>
Wow, I really like your origami :-) I bought one of these keychains from dealextreme, and instead of simple coin cells they contain a 160mAh rechargeable battery ! (about the same dimensions as your 0.33F capacitor). Seems ideal for your project. I've got a question about the inductor you used, the datasheet specifies a much higher saturation inductor, did it work well anyway or did you have issues with the max. current or efficiency ?
Can you post a link to the keychain from dealextreme that had a 160 mAh battery? Did it include the actual charging circuit too? That could be an even better candidate for this project. I will do a test with the breadboarded version and a variable power supply and see if the efficiencies are close to the datasheet's.
This one : <a rel="nofollow" href="http://www.dealextreme.com/details.dx/sku.12932">http://www.dealextreme.com/details.dx/sku.12932</a><br/>Actually, it's 20mAh, and not 160mAh ... It's nearly identical to the keychain you used. It brings me another question : why didn't you use the battery that came in your keychain ?<br/>
or this<br> <a href="http://www.harborfreight.com/mini-dynamo-keychain-flashlight-99859.html" rel="nofollow">http://www.harborfreight.com/mini-dynamo-keychain-flashlight-99859.html</a><br>
I really like the origami, but isn't you motor producing over 5 volts? <br>(therefor shouldn't a step down switching regultor be used?)
Great tutorial : <br> <br>Stupid question, What would happen if you increased the size of the capactor?
Does the step up converter limit current? I have a single 10Ah 3.2V lifepo4 battery left over from an EV project and would love to turn it into a field charger for my andriod tablet
After reading on the data sheet I realize my question is vague. The datasheet shows 500mA in the setup I described, my real question is if I put a large load on this device will it limit current to the 500mA or will it deliver more and burn up?
this &quot;dead bug&quot; packaging is a work of art!
Agreed. I prefer a experiment card as it's easier for me to connect the leads. It seems that I don't have a talent for creating a dead bug!<br><br>Really impressive instructables, it's a piece of art. Thank a lot for that information about MAX756, it'll solve some of my problems about a good 5V source!!!!! :D
I built something like this a while back, but it was with a dead dynamo flashlight that had the little plug on the side for cellphones. I pulled the LED assembly out and hot glued a USB port in its place, soldering it to the pins on the power output on the side
Classic Radio Shack mini-multimeter! I got tired of replacing those coin batteries and modified it to work off three AAA batteries. I haven't replaced them in three years now! Haha.
Great instructable, very clear and well designed! Would any of the other maxim DC-DC converters work for this? The max856 looks like a good alternative.<br>
You know you can find little dynamo keychain things like this that actually have USB out on them. I've seen them on ebay for less than $5. It might be a lot easier to add a battery to one of those than to make a step up circuit.
well done i want that typ of flash light &gt;.&lt;
Really nicely done mate everything with pictures and stuff :D gonna ask around for a dynamo flashlight :P would love to charge everything :D
<p>I DONT GET WERE R1(1) GOES IN STEP 10 (C)</p>
&nbsp;If you look at the 2nd and 3rd picture, D3+ is the end that is being soldered to R1(1).
<p>I was&nbsp;struggling to put&nbsp;a similar max756 circuit&nbsp;with usb in the removable solar panel/battery pack of my&nbsp;<a href="http://www.ikea.com/us/en/catalog/products/90154371" rel="nofollow"><font color="#ff5200">Ikea Sunnan</font></a>&nbsp; lamp, to use it as an&nbsp;PDA-battery backup. <strong>Your origami idea&nbsp;is a very space efficient&nbsp;solution! </strong>( But I wont not solder directly on IC, too affraid to burn it).<br /> <br /> I also plan to hook the battery pack to a forced ventilation woodgas stove ( <a href="http://www.instructables.com/id/Easy-large-portable-woodgas-stove/" rel="nofollow">like this </a>) and use it on&nbsp;a trek in the Spanish Pyrenees.&nbsp;While I'm at it, I could even&nbsp;stick a peltier to the stove and use heat to recharge the battery pack&nbsp;a bit. If I ever get to making an instrucatble of it, I'll link to yours.<br /> <br /> Keep up the good work!<br /> <br /> &nbsp;</p>
Wow!<br /> This Is a very Professional Instructable.<br /> Wonderful Pictures By the Way!<br /> Well Done!<br /> 5 *<br />
great :)
Thank you, Bongmaster.
just got one off ebay and looked inside.. not much space to work with XD gonna see what i can come up with tho :) prolly wont be as compact as ures but i will be making it part of a permanent microcontroller project anyway :)
Hi Griswold Lighting - great Instructable, thank you! A couple of questions, with reference to the the MAX756 datasheet: - if I want the output to be 3.3V, I just need to tie pin 2 to the input voltage (high) by moving its connection to the other side of C3 (or even connecting it straight to pin 1)? - If I wasn't too worried about getting it all back into the case, what's the easiest way to upgrade the stored capacity? Can I just make C3 as big as I can get? I want to hook this to a micro wind turbine to power a small weather station (actually, mainly the XBee that's transmitting the data). Thanks in advance for you help.
- Yup, to get 3.3V you could just tie pins 1 and 2 together. The circuit would work with a micro wind turbine if the turbine is putting out between 0.7V and 3.3V. If the turbine is actually generating >3.3V, you might be able to just use a voltage regulator. - C1 stores most of the energy. If your volume isn't limited you could use a bigger cap for C1 as long as it was rated for at least 5.5V (if you're stepping to 5V) . The charging time will be proportionally longer.
I like the idea. Butttt if you did it with a bike dynamo you could get fit and charge battery. Just a though I think way to much.
A bike dynamo might be the next project. I chose this small size so I could potentially attach it to a development board.
Wow! Nice details and great pictures.
Thanks. I have an SD card filled with pictures of it.
That's fantastic!
Thank you.
is there a way to put an extra 325 ma on this
Not 'as-is' with this tiny motor and circuit...I'd guess the highest it can go is 100 mA. You could probably get 100's of mA with a design based on the larger flashlights.
Great solution!
Thanks NoodlesVA!
Nicely done. I want one!
Thank you. If you have the time it's a fun build.
Thank you very much.
All I need to do is recruit my army of hamsters and connect their wheels to this generator and I can RULE THE WORLD!
An even better reason to use the keychain-sized dynamos....
This is one of the better instructables I've read for procedural details and instructions... and good pictures. Thanks. I'll keep an eye out for the crank lights, sounds like a neat project. And I love the origami.
Thank you. It was a fun project to work on -- it took awhile to find a way to get the parts as compact as possible.
can i use the step up circuit with a 1.5v DC battery?
Definitely. The MAX756 can work with a voltage as low as 0.7V.

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