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I search on electronics.stackexchange.com but I not found an answer.

I want make a output on my keyboard to charge an usb device (ie: mp3 reader or smartphone).

- In first time I want to know if is there a mechanical computer keyboard generating current with keystrokes? (with current generation in keyboard)

- In second time I want to know how is possible to make that?

EDIT #1 : The journal ACS Nano published an article on it in December 30, 2014.

This article describes a keyboard, which can among other features, harvest energy. But the abstract does not reveal the harvesting method and it is not clear if the harvested energy is sufficient to fulfil its own tasks.

EDIT #2 : http://ieeexplore.ieee.org/document/6136691/

This paper presents a hybrid energy harvester which combines piezoelectric (PZT) and electromagnetic (EM) transduction mechanisms to scavenge vibration energy from a keyboard. The system comprises of improvements to the dome structure presented in previous studies, in which only PZT transduction mechanism was used to harvest 16.95 μW of experimentally verified power. An in-house modeling and simulation tool is first introduced in this work to evaluate the integration of EM transduction into the PZT system. The tool combines analytical mechanical equations and FEM results for magnetic fields for the optimization of the electromagnetically generated power. Two designs of different cost are then compared. It is concluded that the design utilizing the frequency-up-conversion technique at an incrementally higher cost is superior due to significantly higher contribution to the generated power compared to the alternative implementation without frequency-up-conversion. Modeling and simulations show an additional 2.81 μW power can be generated through EM integration to the previous PZT based keyboard energy harvester system.

According to user287001 comment:

only 4077 years needed for 1 kWh..

I think (fix me if I mistake) USB device need 500 mA to charge 5V.

- I ask me how many times is needed to charge an usb device?

EDIT : I feel that this question goes beyond me

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Nolwennig
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    It is possible to make, for instance by implementing a solenoid under each key. What do you want it for? – Dampmaskin Jan 16 '17 at 10:33
  • http://www.techeye.net/hardware-2/piezoelectric-keyboard-could-power-your-computer – JimmyB Jan 16 '17 at 10:34
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    @JimmyB I was thinking piezo, too. But, this clickbait article... The title: "Piezoelectric keyboard could power your computer" and the conclusion: "Despite the best efforts of chipmakers, the power drain for chips is still too high for this sort of technology."... You don't say!! – dim Jan 16 '17 at 10:39
  • @Dampmaskin I want make a output on my keyboard to charge an usb device – Nolwennig Jan 16 '17 at 12:29
  • To charge a smart phone: at least 20 years of continuous typing. – polwel Jan 16 '17 at 13:05
  • @Nolwennig Ok, forget about it, then. If you want to charge something just using your muscle's power, make (or buy - it exists) a dynamo USB charger. – dim Jan 16 '17 at 14:04
  • "I think (fix me if I mistake) USB device need 500 mA to charge 5V." If you want to generate enough for 5V*0.5A, that is 2.5W. So you would need about a million keyboards in order to reach that power. However, you don't necessarily need 0,5A to charge an USB device, but at a millionth of the power, you theoretically need a million times as much time. – Dampmaskin Jan 16 '17 at 14:31

2 Answers2

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First, to charge a USB device takes a certain amount of charge, not a certain amount of current. So it might be 500mAh which is 500mA for 1 hour, or 1mA for 500 hours, or 10 uA for 50000 hours (that's about 6 years).

Whatever, 500mAh converted to units of charge (Amp-seconds, or Coulombs) is 1800 Coulombs. And at 5V that's 5 * 1800 = 7200 Joules.

Now let's assume you can design a perfectly efficient keyboard. My full size keyboard has a key travel of 4.5mm and AS NEAR AS i CAN MEASURE (sorry I measured the caps lock key) about 40g or 0.4N to operate the key. So each key press requires 0.4*0.0045 joules, or 0.0018 Joules.

So after 7200/0.0018 keystrokes, or 4 million keystrokes, your device will be charged. Assuming you manage to convert all that energy into electrical power with 100% efficiency.

And you'll have written the Lord of the Rings.

Twice.

  • And unfortunately, the self-discharge of the device will probably be faster than the rate at which you can charge it with this method. You'll be doomed to write and rewrite Lord of the Rings as fast as you can. Forever. – dim Jan 16 '17 at 19:34
  • A million monkeys charging a phone while writing a new novel. –  Jan 16 '17 at 20:11
  • I wonder how many Wh the average typist produced during a work day in front of a mechanical typewriter back in the days... – JimmyB Jan 17 '17 at 13:13
  • [@Brian](https://electronics.stackexchange.com/users/16324/brian-drummond) I will use children slide on toboggan instead ;) – Nolwennig Oct 26 '17 at 08:29
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http://ieeexplore.ieee.org/document/6136691/

This paper presents a hybrid energy harvester which combines piezoelectric (PZT) and electromagnetic (EM) transduction mechanisms to scavenge vibration energy from a keyboard. The system comprises of improvements to the dome structure presented in previous studies, in which only PZT transduction mechanism was used to harvest 16.95 μW of experimentally verified power. An in-house modeling and simulation tool is first introduced in this work to evaluate the integration of EM transduction into the PZT system. The tool combines analytical mechanical equations and FEM results for magnetic fields for the optimization of the electromagnetically generated power. Two designs of different cost are then compared. It is concluded that the design utilizing the frequency-up-conversion technique at an incrementally higher cost is superior due to significantly higher contribution to the generated power compared to the alternative implementation without frequency-up-conversion. Modeling and simulations show an additional 2.81 μW power can be generated through EM integration to the previous PZT based keyboard energy harvester system.

That's really not a lot of power. About the same as the tiny solar cells on calculators.

pjc50
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    only 4077 years needed for 1 kWh. This could be available today if Ramses the 1st had taken the right equipment into use. –  Jan 16 '17 at 11:37