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Pizoelectrical Flashlight concept help

  1. Aug 20, 2013 #1
    Hey guys, I have been thinking of creating a flashlight that is powered by piezoelectric (pressure) energy. I have watched several videos so far and I noticed that in order to actually generate electricity, one would have to constantly tap it rapidly in order to power an LED light.

    However, I want to try to minimize the input requirements of rapidly tapping the pizoelectrical sensor. I know that pizoelectrical sensors generate electricity by being deformed so I was thinking of ways to try to still deform it and generate electricity with smaller and more gentle/effortless movement. The main idea is that I want to reduce the effort needed by the user to power up the flashlight, without rapidly charging it for immediate use or charging the device.

    -I was thinking of trying of either trying to use small stroking/rubbing movements where a small flexible mat with multiple points at the bottom can deform the sensor. If that is not enough force, then I would have to figure out someway to get mechanical advantage.

    -Some kind of small wheel has some points on it and when you roll the wheel back and forth, the teeth at the end would deform the pizoelectrical sensor.

    -Some sort of mechanical advantage to reduce the tapping force of the user and using mechanical advantage to raise the force of the minimize tapping motion to meet the LED's requirements. I wonder if a spring can be useful here.

    Will these ideas work? Do you have any better methods I can use?
    Last edited: Aug 20, 2013
  2. jcsd
  3. Aug 20, 2013 #2


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    Staff: Mentor

    Remember that the energy out (in the form of light) can't be any more than the energy in (in the form of work done by the person working the flashlight). So the best mechanically powered flashlight would be one where the user could comfortably work a crank or other ergonomic & mechanically efficient mechanism to put energy into the flashlight. Work is force through a distance, so tapping a thin membrane is not going to efficiently let you do work. You need a longer distance to apply the force through to efficiently convert human power to electrical energy.

    Having said that, you might look at ways to convert longer motion by the human into higher frequency "taps" on the piezo strips to see what the relative efficiencies are compared to just turning a dynamo lever. I don't think it would be more efficient, but more detailed investigation might prove me wrong...
  4. Aug 21, 2013 #3
    The key to make the pizoelectrical flashlight more efficient than a flashlight with a crank is to somehow use multiplied force or somehow increase the oscillation of the membrane. The pizoelectrical sensor can generate electricity by it simply vibrating and being deformed, so somehow getting the membrane to oscillate more with minimal effort would help. I don't think that multiple taps rapidly are really needed, but the act of getting the sensor to deform and vibrate more is. I need to figure out a way to produce more force or maximize vibrations through a single tap. The goal is to have the user apply minimal effort (gentile and light taps or gentle strokes) to operate the flashlight.

    I feel like using a machine with mechanical advantage that multiply force and distance is the key to getting this flashlight to work. That or getting more vibrations

    I also realize that velocity (as well as mass) could contribute in producing more force (momentum formula). With that said, I think that a using a wheel that the user can roll back and forth constantly that strikes into the membrane can help increase force. Distance is still something I need to consider though.

    I know that I have to somehow incorporate distance, so I was wondering, how does a crankable flashlight apply distance? The length of its crank?

    I believe that this problem can be solved through through thinking and innovation, it's not really a complicated problem to solve, I just need to figure out a way to do it. Mind if you give me a few pointers on the application of distance in machines and power generation? I need to learn how to apply distance more in order to get this to work.
  5. Aug 21, 2013 #4


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    Staff: Mentor

    I think you're missing a critical issue here: conservation of energy applies. You can multiply force with a lever, but you can't multiply energy and any power generator converts mechanical energy to electrical. So when you set the sensor vibrating, then start to extract electrical energy from it, that stops the vibration. I have a pair of skis that dampen vibration that way.

    Hand-crank generators are pretty efficient; much more than a piezo generator would be.
  6. Aug 21, 2013 #5
    Like I said, I need to figure out a way to have the sensor constantly vibrate, and at the moment, the most common way is to rapidly slam your finger into the membrane multiple times. I want more efficent tapping.

    The multiplied force will create the same force of a slamming of a finger with smaller movements of the user.

    Now the problem is that that I need to get the sensor to vibrate more. This is why people constantly tap it to light up an LED. The problem to solve is how can I create "mutltiple taps" with minimal effort. I think that the ability to create the same amount of force within each tap by smaller tapping movements makes it less annoying for the user to rapidly strike the membrane, but I want to try to accomplish more and figure out a way to create more vibrations. This is one of the reasons why I suggested the wheel idea, a wheel rolled back and forth and strike the membrane multiple times for more vibrations. If each strike of the wheel can be the same force as the tapping of a finger, then this can actually help create enough work with minimal effort of the user.
  7. Aug 21, 2013 #6


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    Staff: Mentor

    What does "more efficient tapping" mean? There is a certain force and a certain displacement. This mechanical motion is what it is; there is no efficiency associated with it.
    If you use a lever to decrease the distance, you increase the force.
    Impossible. Conservation of energy and the functioning of levers prohibit that. If the movement is smaller, the force must be larger.
    I think you may also be misunderstanding that force is not work. Work is force times distance.
  8. Aug 21, 2013 #7
    When I said more efficient tapping, I meant lighter, less rapid, and smaller taps instead of rapidly tapping it hard.

    What do you mean by decrease the distance? Like reducing the length of the lever? Reducing the height of the finger/tapping head?

    I am not saying that I am getting rid of distance or reducing it, I am saying that the taps should have less distance to make the user comfortable, but get the distance and force from somewhere else. For example, I was thinking of a single tap that would slam a long hammer into the membrane like a typewriter or piano hammer (once the hammerhead have more mass). The tap itself isn't going to power up the flashlight, a simple machine will help maximize the output of the user.

    Yeah, the wheel thing was a sample idea to a design, I didn't think it would work at this stage yet. If I could figure out a way to incorporate distance into that, then it may have potential.
    Last edited: Aug 21, 2013
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