There might be an MCU in this design to help manage energy, but even if there is no MCU, this nifty device is a great fit with our tagline: "Changing the world, bit by bit." It is a gravity-powered LED designed for rural areas far from power utilities, and scheduled for field trials in Africa.
The device came to my attention through a reader post here on Microcontroller Central. (For those who don't know, there are Reader Message Boards where you can start up discussions of your own. Click on "Messages" above the orange line, then on "reader boards" on the page that comes up.) I thought it was a marvelous idea as well as a clever bit of engineering. It is the GravityLight, and it aims to bring reliable, low-cost electric lighting to rural areas.
Basically, this is an LED lamp with a dimmer and a built-in generator. The key thing is that the generator is powered by gravity, using a falling weight as in a grandfather clock to create up to 30 minutes of lighting. No battery. No hand crank. No solar panel. It can be set up and used virtually anywhere, and only needs user action every half hour or so to keep the lights burning. From the video it appears to be fabricated mostly out of high-strength plastic, including the gearing that turns the slow drop of the weight into the fast spin of the generator that provides the electricity. If there is an MCU in there, it probably serves to control the LED drive circuitry.
There are several things I admire about the engineering that has gone into this design. One of them is the abandonment of the more traditional battery approach to use pure energy harvesting to power the light. Another is the efforts made to keep the design simple and rugged to maximize its field life. Cost-saving measures such as re-using the storage bag as the weight holder, and using local dirt or rocks as the weights, are another noteworthy touch.
The GravityLight is still in prototype stage, and the creators, who work for design consultancy Therefore, are looking for funding. They aim to fabricate a prototype run of 1,000 units for donation to villages in Africa, where they will provide the villagers with free electric lighting and the creators with a field trial of their design. Their funding effort with Indiegogo runs through January 15.
Aside from the great social benefit this design can provide, I am impressed with its merits as a commercial product. I can imagine backpackers, for instance, carrying one along instead of gas lanterns or batteries. It would also make a great compact emergency light for home use. It could have been very handy for those folks without power on the US East Coast after Hurricane Sandy a few months ago.
MCU or not, this seems to me worthy of mention here as a well-thought-out bit of design engineering. Simple, elegant, functional, practical, durable, and inexpensive. Wish I could have done half so well with my efforts.
Rich Quinnell 12/21/2012 3:27:44 PM User Rank Blogger
Re: Quick Computation
If I have guessed correctly, this light uses the weight to slowly turn a gear, that causes a faster gear motion at the generator to generate sufficient voltage. I doubt there is a flywheel or other energy storage, except maybe a supercapacitor for keeping the light going while the weight is being raised. But there is no way the system can raise the weight by itself to reset itself for an additional half hour's operation. That would violate conservation of energy.
Davidmicro 12/19/2012 3:55:44 PM User Rank Program Manager
Re: Quick Computation
Exactly, so, initial energy comes from user actions that are pulling the pre-loaded weight to turn light on, I guess that we might use Gyro concept to store the moment energy that user forces. But, it is very crucial to calculate power consumption of mechanical behavior by experiment in my opinion.
Rich Quinnell 12/19/2012 2:23:10 PM User Rank Blogger
Re: Quick Computation
Not sure I understand what you mean in your proposal. You mentioned in your original post the MCU periodically sending the pre-loaded weight in the other direction. So, do you mean having it fall, then rise, then fall again? You would need an input of energy in order to make it rise.
Davidmicro 12/18/2012 10:28:40 PM User Rank Program Manager
Re: Quick Computation
->only needs user action every half hour or so to keep the lights burning
my intention is to minimize or remove your action every 30 [min] by using MCU. Gravity action might be automatically controlled. Of course, at the first time, your action is required to turn light on. After that, all internal mechanism is automatic, until user action is triggered to turn light off. Does this method violate Energy Conservative Law?
Rich Quinnell 12/18/2012 11:56:58 AM User Rank Blogger
Re: Quick Computation
David, ultra low-power MCUs are available and a supercapacitor could store enough charge to run the MCU for a while, but why bother? If you want the light to stay primed and ready to come on only when needed, you could add a simple light sensor and have it controlling latch or brake on the weight mechanism. The ambinet light would provide the power needed to do so, and when ambient light faded the brake would release and the gravity light take over. Still seems an unnecessary complication, though, for the intended application.
Davidmicro 12/17/2012 9:53:41 PM User Rank Program Manager
Re: Quick Computation
I guess that power energy should be calculated correctly for using MCU. But let us assume that this system can provide enough energy sources to ultra low power MCU for a certain period. Then as implementing the timer with switch, automatic triggering light might be designed without using hand continuously every time. To do this type design, an appropriate weight should be pre-loaded. Output of MCU commands the switch to go pre-loaded weight to other direction, when timer is expired. Timer control bit is configured at MCU.
Rich Quinnell 12/17/2012 3:09:57 PM User Rank Blogger
Re: Quick Computation
You may well be right that the mechanics of the generator in this design could be scaled and adapted to provide more electricity and use a different mechanism to drive the generator. I'll bet someone could come up with a mechanism that could work that way. I can envision a giant hourglass type mechanism where sand trickles into a bucket on a wheel that turns a gear to pull the strap that goes through the light. It could be pre-loaded with sand enough to run for hours and perhaps power multiple generators off of the same wheel.
These guys, though,were looking for a low-cost, portable, rugged one-person mechanism that could use whatever was at hand to form the weight driving the generator. It's a specific set of constraints that solar and batteries don't address. Needing water is an issue, as well, and even if you get past the supply issue you need to find a way to raise that water to a height and store it there to run the generator. As to using a fine powder as a fluid, we then have the problem of airborne dust to face. That dust is both an irritant to the users and potentially damaging to the mechanism.
Within its target constraints, I think it is a pretty good solution.
Rich Quinnell 12/17/2012 2:51:14 PM User Rank Blogger
Re: Not exactly "Harvesting Energy"...
You have valid point about not calling this "energy harvesting" in that this involves the deliberate input of work to run the system. As this requires the continual input of human energy that would not otherwise have been involved, it is probably better described as "pure generation" (as opposed to needing batteries.)
Massimo Manca 12/17/2012 2:49:26 PM User Rank Blogger
Re: Quick Computation
@Rich: sure, it is only for individuals but the point is that it delivers too little energy. I know that Africans have problems also with water but wait just a moment and suppose they have.
If you can transform gravity in electrical energy you need some sort of generator so I suppose that their idea is to move a rotational generator with a weight coming down at low speed. But more energy you need more heavy the weight have to be and more difficult is to move it when it will be on the floor. So, the answer is a "home made dam" with a generator that should be a nano turbine or may be a simple wheel, it doesn't matter so much because also if the gain is a lot under of unity it makes possible to move more weight with less (unitary) effort.
So, the problem should be to use a different fluid because there is not so much water in Africa to use at home to produce electricity. May be that with very fine powder it can work quite well and so they should generate more energy for more time.
Rich Quinnell 12/17/2012 2:09:06 PM User Rank Blogger
Re: Quick Computation
Massimo, I think they mention that 30 minutes is the run time, not an hour, and the problem with batteries is their cost and need for replacement. Depending on how rugged this is, it could last for years with no need to replace anything.
For an entire village the solar system you propose might make the most sense. I get the feeling this is intended to be an individual solution.
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