Small balcony windmill to power Arduino (or ATtiny85). Feasibility?

Hi, I'm looking for some early inout and feedback on a project I have been thinking about lately. See below for background and questions. Your input would be very welcome.

The idea I'm thinking about building a small windmill on the balcony to power my arduino, or (better) an ATtiny85. The idea is to collect energy from the windmill and store it in a capacitor. When the capacitor is full, it will somehow discharge and power the microcontroller which does some kind of computation (still to be defined what, but let's say blink an LED).

The approach My basic idea is to glue magnets to a disc and have them rotate over some coils to generate electricity when the wind turns the mill. The electricity will go into a bridge rectifier and then into the capacitor as described above.

To get me started I already bought these - Bridge rectifier http://www.kjell.com/content/templates/shop_main_details.aspx?item=90050&path=239000000,266000000,268000000 - 4 x Ring magnets http://www.supermagnete.de/eng/R-15-06-06-N

I also have a 5V super capacitor lying around somewhere.

Questions:

A - Is this feasible? Is there a better way to do this? General thoughts?

B - What kind of coils and how many should I use? 1 coil? 2 coils? 4 coils? How should I hook them up to the rectifier? Where can I source the coils? Make myself? How?

C - Any pointers to similar projects? I did some naive googling, but didn't find anything useful. I bet I'm not the first though. All/any pointers welcome

Thanks/Anders

Check - http://www.instructables.com - for windmill designs that drive a small dynamo.

e.g. - http://www.instructables.com/id/DIY-1000-watt-wind-turbine/ - ??

You couldn't find any hits on home made generators? Try again. The windings you make will determine the voltage & current you can create. Go take a look at a bicycyle generator, get some construction ideas.

Luckily you only need 5V, 50mA or so.

Luckily you only need 5V, 50mA or so.

1.8V (low voltage version), less than 8mA for the processor.

"1.8V (low voltage version), less than 8mA for the processor."

Aruino would have to drop to 4 MHz for 1.8V. I have no ATTiny experience. Gonna make interfacing to any thing a challenge at 1.8V.

CrossRoads: Aruino would have to drop to 4 MHz for 1.8V. I have no ATTiny experience.

Ditto for the Tiny.

which does some kind of computation (still to be defined what, but let's say blink an LED)

Gonna make interfacing to any thing a challenge at 1.8V.

But perfect for an LED. And the extra low power consumption would allow the application to run long after the wind stops.

As others have said, the internet is FULL of winding / generator / blade howto's. There are a ton of variables to tweak in the design to determine exactly how much power out.

No matter what you do, though, you'll have enough power to make an ATTiny power up for a second or two. Storing in a capacitor is perfect for this. How long the charge / voltage in the capacitor is good for really will determine on the load your ATTiny is controlling as the ATTiny will (more than likely) use a fraction of the power your load will.

Good luck!

Ok, thanks for all the input and pointers. As usual, I got some new angles that I hadn't thought of before hand.

Several challenges for me as a newbie in this one. No idea how to trigger the discharge of the capacitor when ready for instance, but I guess that will be a specific topic for later.

Thanks again!

//Anders

No idea how to trigger the discharge of the capacitor when ready for instance

Will you need to? If the power consumed by your gadget is less than the typical power provided by the generator, won't the capacitor charge from the excess power?

What do you mean by discharge? I was under the impression you were just using it like a battery.
Does the attiny have brown out detection that you can set so the chip does not attempt to power up when the source voltage is too low?

CrossRoads: Does the attiny have brown out detection that you can set so the chip does not attempt to power up when the source voltage is too low?

Yes. It is similar (or identical; I'm too lazy today to go check) to the one in the ATmega328.