# Rainy Day Fun by Calculating Pi

If you need a truly random event generator, just wait till your next rainstorm. Whether any given spot on the ground is hit by a drop at a particular time is anyone’s guess, and such randomness is key to this simple rig that estimates the value of pi using raindrop sensors.

You may recall [AlphaPhoenix]’s recent electroshock Settlers of Catan expeditor. The idea with this less shocking build is to estimate the value of pi using the ratio of the area of a square sensor to a circular one. Simple piezo transducers serve as impact sensors that feed an Arduino and count the relative number of raindrops hitting the sensors. In the first video below, we see that as more data accumulates, the Arduino’s estimate of pi eventually converges on the well-known 3.14159 value. The second video has details of the math behind the method, plus a discussion of the real-world problems that cropped up during testing — turns out that waterproofing and grounding were both key to noise-free data from the sensor pads.

In the end, [AlphaPhoenix] isn’t proving anything new, but we like the method here and can see applications for it. What about using such sensors to detect individual popcorn kernels popping to demonstrate the Gaussian distribution? We also can’t help but think of other ways to measure raindrops; how about strain gauges that weigh the rainwater as it accumulates differentially in square and circular containers? Share your ideas in the comments below.

# Shapeshifting Material For Weather Adaptive Structures

Where [Isaac Newton] had his apple (maybe), [Chao Chen] found inspiration in a pine cone for a design project that lead to a water-sensitive building material. He noticed the way some pine cones are sensitive to water, closing up tight when it rains, but opening up with dry conditions. Some dissection of a pine cone revealed [Mother Nature’s] solution – different layers that swell preferentially when exposed to moisture, similar to how a bimetallic strip flexes when heated. [Chao Chen’s] solution appears to use balsa wood and a polystyrene sheet laminated to a fabric backing to achieve the same movement – the wood swells when wet and pulls the laminate flat, but curls up when dry.

As [Chao] points out, the material is only a prototype, but it looks like a winner down the road. The possibilities for an adaptive material like this are endless. [Chao] imagines a picnic pavilion with a roof that snaps shut when it rains, and has built a working model. What about window shutters that let air and light in but close up automatically in that sudden summer storm? Self-deploying armor for your next epic Super Soaker battle? Maybe there are more serious applications that would help solve some of the big problems with water management that the world faces.

Make sure you check out the video after the break, with a more decorative application that starts out looking like an [M.C. Escher] print but ends up completely different.

# Visual rain sensor — so you never have to look outside

Now you can find out how hard it is raining outside without leaving the confines of your mancave/womancave. Pictured above is the sensor portion of what [Frapedia] calls his visual rain sensor.

Most rain gauges just use a graduated cylinder to capture water as it falls from the sky. That will give you a reasonably accurate measure of how much it rained, but it tells you nothing about how hard it rained. The measurement made here is based on sound. The harder it rains, the lounder the sound will be from water hitting an up-turned metal bowl. The unit above turns the system on when water bridges the traces, then a microphone is used to monitor the sound from the bowl. This is visualized by a VU-meter chip on a column of LEDs mounted inside the house.

After the break you can see the project box that houses the status display. We say it’s too small an needs to be replaced with a much larger LED meter.

# Lighting LEDs with raindrops

[Steven] had one of those musical gift cards laying around, and thought he might as well reuse the piezo speaker inside it. Without a particular project in mind, he soldered an LED to the piezo and tapped on it, which caused the LED to illuminate as expected. He started to wonder what quantity of force would be required to light the LED, and if it could be done by a raindrop.

He first tested his theory in the shower, and as you can see in the video below it actually worked, though the light was dim and sporadic as you might imagine. He eventually discovered that for optimal lighting, the piezo worked best when struck by single droplets falling with pauses in between, from a minimum height of 4 feet. To achieve a water flow within those specifications, he built a rain funnel so that he can control the droplet frequency and intensity.

It seems to work pretty well from what we can see. Off the top of our heads we can’t seem to come up with any practical applications of the water powered LED, but it is an interesting set of experiments nonetheless.

Have an idea to use this setup that we totally missed? Let us know in the comments!

[Thanks, Rob]

# Blade Runner umbrella saber

Here’s a Blade Runner umbrella build that is done just a little bit too right. It delivers a double-dose of geekery with its lightsaber-gone-rain-protector look but where we think it crosses the line is at the built-in audio system. When you turn it on it plays recordings of popular lines from Blade Runner, something that might not fly in public. But the quality is in a different galaxy compared to the dollar store illuminated umbrella that we looked at last year.

[Erv’ Plecter] replaced the central support rod for the umbrella with a clear polycarbonate tube. An optic cable snakes through the hollow tube, illuminated by a Luxeon LED in the handle. The custom PCB and 900 mAh battery are both housed there as well. Take a look at (and listen to) the demo after the break. We’ll need to add this to our future projects list right after that Lightsaber movie replica build.

# Beach stereo

[Adam] wanted a stereo that could stand up to rain and keep sand out. He ended up building this beach stereo out of a cooler. The cooler’s already made to be water tight. He cut holes in the front and back for marine speakers and added a water-tight bezel and cover for the controls on the deck. Inside you’ll find a marine battery to power the unit. Now he and his friends can rock-out even in poor weather thanks to this portable and rugged unit.

# Motorcycle visor rain disk

[andrew] sent us this proof of concept. Based off of the Spiech Clear view screen, used in marine applications, it uses a spinning disk to keep a part of your vision free of water droplets. While you may not be too impressed by watching the video initially, keep in mind that this was a quick prototype. With some planning and a little work, this could be moved to a more convenient location and run by a side mounted motor. It could even be made to be removable for fair weather. It probably doesn’t do so well with mud though.