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]


40 thoughts on “Lighting LEDs With Raindrops

    1. That was my idea. But it’s a good idea, I would love to see something like that just lineing a pathway. Could do a solar power backup so it lights up at night, or when it’s raining.

    2. i think having them charge a capacitor solar engine style and using bright white leds would work well also. Depending on the capacitor, you would get bright pulses once every few seconds instead of lots of dim pulses that are hard to see.

  1. Put a counter weight on one side of the speaker and mount it on a vibrating surface.
    Wouldn’t this be enough force to generate electricity by driving/music/washing machine/…?

      1. NASA is actually looking into the matter. I remember reading about some physics student program they had where they developed methods of making really loud noises out of heat.

        The idea is, that you could develop a pistonless engine that creates just really loud vibrations and turns them into electricity, and put that in a satellite.

  2. Perfect for underneath my shower tray! I was wondering how I could see if there was a constant drip. If I make a grid of piezo buzzers and connect them to an LED matrix, not only could I remotely see if there was a drip, but I could get an idea of where it is exactly! (and it doesn’t consume power and would be electrically safe).

  3. The simplicity is neat.

    I wonder about a battery + transistor + solar cell to allow the LED the fire brightly. The battery and solar cell could be scavenged from those cheap yard lights and could probably power quite a few LEDs. I know that loses the ‘zero power’ elegance… I wonder if the PZ could be used as a switch, eliminating a transistor per PZ?

    Seeing a matrix of those from above, in subdued light, could be really cool. It should allow you to see the instant arrival of each striking droplet…

    Btw, many of the musical cards now feature “real” speakers, rather than PZ. I actually had trouble finding PZ versions while building hydrophones in Alaska to record whales. The hallmark cards were speakers, while the off-brands were PZ.

    Could you mount these on a bike helmet? The front of a car? Wind pressure on the PZ might be a problem.

  4. Could you use say 20 piezo to charge a capacitor over time that could then be on a discharged to leds to light say a stairwell for maybe a min or 2.
    put piezos under your rug in a hallway as you walk you charge the cap, a sensor says when you are about to hit the stairs and discharges the cap to the led strips to light the stairs for a few moments alowing enough time to get down the stairs safely…..
    just an idea with plenty of room to work and improve

  5. I’m pretty sure they don’t use piezo here, but this is kind of the idea…

    “Water is a huge part of our everyday lives. We use it almost without thinking: showering, brushing teeth, doing dishes, running the sprinkler. But what if we could collect energy from these everyday uses? With Splashpower, we can.

    A miniature hydroelectric technology innovation, Splashpower has the potential to dramatically impact the environment by harnessing power from everyday water usage.
    For example, a standard household faucet delivers roughly 24 watts of power. Splashpower can draw almost 70 percent of it for use in other applications. Water has never been so green!

    Splashpower opens the door to countless applications and design possibilities. Imagine no wires for sprinkling controls; automatic valves with no power needed; water toys with no need for batteries; and the list goes on. With both inline and end of stream solutions, power can be efficiently delivered to almost any appropriately adapted electrical device without the traditional constraints of batteries or cords. Splashpower is the technology that puts water to work.”

  6. My idea – put multiple piezos on an umbrella with the LED’s on the underside. Seal up the holes that the LED pokes through with silicone. On a hard rain, you might get an interesting twinkling affect.

  7. “Rain-glow” lighting- how cool! I love the rain and to have choreographed twinkling to accompany the falling drops . . . this could be awesome! I know what I’m making this weekend ;)

  8. Imagine adding this rainpower-harvesting capability to PV solar cells, or even roof shingles – a sheet of transparent piezoelectric material spread across each cell or shingle might add up to something worthwhile.

  9. Quick note, if anyone’s thinking of setting something up like this & leaving it outside for a long time – put conformal coating or something over the legs of the LED because they’ll most likely rust.

  10. Hook it up to an optical counter and make an optical rain gauge. With a few of these you could probably measure rainfall much more accurately than your typical home rain gauge setup. It would probably work especially well for low rainfall amounts, which are the hardest ones to measure.

  11. Rain gauge. The constant periodic drip with the funnel would give you a great rounded stat for how much rain is falling and when.

    Or put several in a sealed tube, you can have lights twinkle as the water splashes it’s way down the tube from sensor to sensor.

    That… might be something I have to build!

  12. If he put an infrared LED on this, instead of read and yelled real loud at the piezo he could have the worlds simplest infrared voice transmitter! (Although people would probably be able to hear him yell father than his infrared signal would transmit, if at all.)

  13. So this is where all that traffic came from! I’m the Steven one who did this piezo and raindrops experimenting. Thanks for pointing it out here and I’m glad to see it generated so much interest. I look forward to seeing what others come up with as a result.
    PS. Cool website you have here!

  14. Turn the water into a more direct application of kinetic energy.
    Let the watter accumulate in another container balanced on a tipping point.
    (Zen bamboo-garden-water-drum feature for example)
    When full, the balance will tip – emptying the water and have the other end of the balance strike the piezo. Thereby light…

    to improve the electronics to get a brighter light – use a converter to turn the very high voltage peak into a lower voltage higher current signal…
    Using devices like the LTC 35881 (pdf warning

    1. If you have downspouts filled with water from your roof then you can take this idea one step further and have a wheel of buckets. As one fills up, the wheel turns a few degrees to position the next bucket while a striker hits the crystal at a fairly rapid rate. With a circuit it may be able to keep the light lit continuously.

      Sadly we have a flat roof and our roof water drains through the sewer-gas vents in the roof straight into the sewer; no downspouts.

  15. These could be built into the reflectors that are placed alongside the road, so that when it rains, the traffic lines/lanes are easier to spot.

    I know here in Florida they’re using a new road paint (vs what was used 10+ years ago) that is magnitudes harder to see at night when it rains, thus making traffic lines more difficult to spot. Also, something about the reflectors changed, so they’re not as reflective.

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