A Low Cost, Solar-Powered Swamp Cooler


A looming, torturous summer is preparing to bear down on many of us, making this dirt-cheap swamp cooler build an attractive hack to fend off the heat.

Though this is a pretty standard evaporative cooler, the design comes together in a tidy and transportable finished product. The base is a ~$3, 5-gallon bucket from a local hardware store with its accompanying Styrofoam liner. Three 2 1/8″ holes carved into the side of both the bucket and liner will snugly fit some inch-and-a-half PVC pipe with no need for glue.

One last cut into the lid to seat a small desk fan rounds off this build—or you can chop into the styrofoam liner’s lid if you prefer. The video demonstrates using a 15W solar panel to run the fan, and we have to admit that the cooler seems to be an excellent low-cost build. It does, however, require a frozen gallon jug inside to pump out the chilled air for around 5-6 hours per jug. Maybe one of our frugal and mathematically-inclined readers can throw out some guesstimations for the cost of stocking the bucket with a jug of frozen water a couple times a day? Video after the jump.

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CartoLucci: A Candle-Powered Christmas Card


If you’re looking for a last-minute Christmas present, you probably won’t have enough time to reproduce [Helmar's] candle-powered Christmas card. He’s been working on it for a few years now, since his first prototype in 2010. Though he pieced together the original card with parts lying around his workshop, the most recent iteration looks like it belongs on the shelf in a store.

We last saw [Helmar's] work two years ago, when he shared his Full Color Laser TV. This project is a bit more compact: the circuitry was printed with conductive ink on the cardstock, and all the required components are held together by conductive adhesive. To power the electronics, he decided against a battery and instead chose to embed a solar cell on the inside of the card. Placing a lit candle inside the open card provides enough juice for the exterior of the card to shine.

You can see a video of both the current and prototype versions of [Helmar's] cards after the break.

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Solar Powered, Tweeting Bird Feeder


The folks at Manifold created their version of a tweeting bird feeder, and [Chad] wrote up a behind-the-scenes of their design. The goal is something we’ve seen before: When the bird lands to eat, take a picture and tweet it. In this case, they had some corporate money behind the project, and that allowed them to buy a nice solar panel and battery pack to keep the whole thing running.

The write-up is full of the experimentation that we all enjoy: They found that detecting motion through the camera feed wasn’t reliable, so they switched over to a PIR sensor. The PIR sensor was too sensitive to heat changes during the day, so they went with an ultrasonic rangefinder, but wind caused issues there. They finally came up with a solution which involves using two sensors to confirm motion. This seems a bit more complicated than it needs to be, but it works well for them.

We think it is nice to see companies getting behind quirky projects. All told, they spent dozens of hours on this, and they chose to give all of their findings back to the community in the form of thorough explanations and project diagrams. It would be nice to see more of this.

The weather in Colorado hasn’t been the best lately, so the birdhouse hasn’t been tweeting for a while. In our experience, a project that’s turned off is in the dangerous position of being scavenged for parts. Hopefully that isn’t the case here, and we will see it back in action when Spring starts.

Hack a Solar Garden Light Into a Flashlight


While browsing through his local dollar store, [Taylor] came across a suspicious looking rock that, upon closer inspection, turned out to be a solar garden light. He scooped it up, took it home and cracked it open, modding it to function as a handheld solar flashlight.

Inside was a pathetically small 40mAh rechargeable battery, which he upgraded to a more standard rechargeable AA. The garden rock came pre-built with its own boost converter to kick up the voltage for the LED, but it was fairly dim. We’re guessing [Taylor] didn’t bother reverse engineering the converter and instead simply did some trial and error, but he managed to increase the LED’s brightness by slapping on a different value inductor.

As fun as it may be to have a rock for a flashlight, [Taylor] decided to cobble together a custom case out of a spare USB charger, making a battery holder and adding a pushbutton. The result is a handy solar flashlight that takes around five hours to charge. Check out some other custom lights: a lithium-powered PVC flashlight or one with a snazzier aluminum body and interchangeable heads.

Making keys after the apocalypse


Making keys is an amazing art with a lot of skill and technique involved. For those of you living in a post-apocalyptic world, [Dan] has a much simpler solution to the problems of having one too few keys for your locks and deadbolts – just cast them out of scrap with the power of the sun.

To make the mold of the key, [Dan] is using a two-piece plaster of paris mold. First, a thick layer of plaster is laid down in a small container and the key floated on the surface. After drying, sprues are put in with clay and the key embedded in a curing plaster block. After a few hours, a proper mold is created ready to receive molten metal.

The casting material is zinc – not as hard as the original steel key, but more than strong enough to turn a lock. This zinc is melted in a steel and plaster crucible with a gigantic fresnel lens.

As for the utility of this method of copying keys after the apocalypse, we’ll have to wonder how practical this method is. A giant fresnel lens isn’t just something you randomly find unless you’re going house to house looking for projection TVs, and finding a can of mold release after the end of the world is beyond credulity. That said, it’s a cool demonstration of metal casting that can be easily accomplished at home or at any hackerspace.

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Hardware store goods and an mbed combine help solar panels track the sun


If you have the space, and can build a tracking rig cheaply you’ll be able to get a lot more out of your solar panels. That’s because they work best when the sun’s rays are hitting them perpendicular to the surface and not at an angle. [Michael Davis] hit both of those stipulations with this mbed powered solar tracker.

At a garage sale he picked up an antenna motor for just $15. The thing was very old, but still wrapped in the original plastic. It’s beefy enough to move his panels, but he first needed a way to mount everything. After checking his angles he built a base out of wood and used galvanized water pipe as an axle. Cable clamps mate his aluminum angle bracket frame to the pipe. This frame holds the panels securely.

To track the sun he used two smaller cells which aren’t easy to pick out in this image. They are monitored by the mbed microcontroller which measures their output in order to point the assembly in the direction which has the most intense light. A couple of limit switches are included to stop the assembly when it reaches either side.

This technique of using small solar cells as the tracking sensors seems to work well. Here’s another project that took that approach.

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Solar powered hovercraft


It looks a little bit like an octocopter, but this solar-powered hovercraft is distinctly different from its free-flying brethren. It depends mostly on ground effect for operation and to get it just a bit into the air you need a pretty large reflective rig nearby.

The vehicle needs to be even lighter than traditional quadcopters in order to function. It doesn’t carry any battery at all which presents a problem when trying to program the microcontroller board. For this it is connected to an external battery, which is removed before flight so that the control can be powered from the solar array.

What’s not shown in the image above is a mirror array used to focus more intense sunlight on the panels to bump up the available electricity. Not much is said about this, but there is one image on the project page which shows the creator standing in front of the set of four mirrors (perhaps sheets of mylar?) strung up between a couple of trees.

Alas, we couldn’t find a video of the aircraft in action. With such a delicate balsa wood frame we’re sure this thing is affected by every air current that passes its way.

[Thanks Laimonas]