Here I will post a few simple to build FE related projects.
But it is not so simple understand how they work ;)
How to build Kulibin's fountain
(about inventor https://en.wikipedia.org/wiki/Ivan_Kulibin)
Gravity assisted battery
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Under gravity influence concentration of salt in water depends on height same as air pressure
depends on height. If we insert two electrodes in the tube, one near top and one near bottom, due
to difference in ions concentration some EMF appear between electrodes and if we close circuit
there will be some electric current flow. In such buttery plus will be on top terminal and minus
on bottom terminal. If you turn it upside-down polarity will change. I think if we periodically
turn such battery upside-down, polarity will change periodically and we can control (reverse)
processes on electrodes and avoid chemical destruction. So, theoretically, such battery can have
quite long life time.
Flower Power – unusual battery design
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Some years ago I saw an article in Nuts & Volts magazine where somebody used flowers as
power source. It said that if you connect one wire to the ground and one to the flower's top
leaves some voltage appear and very small current can be obtained. This article puzzled me a lot.
It is not typical chemical battery like "lemon" battery which works similar to regular batteries.
I made some information search and to my surprise found that it is well known fact...
Perpetual blinker
Combination of Joe Tate Ambient Power Module (http://www.rexresearch.com/tate/tate.htm) with LED flasher circuit.
"Drinking" clock
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I think everyone knows about "Drinking bird" toy (https://en.wikipedia.org/wiki/Drinking_bird).
Here I would like present "modern", solid state analog :)
Take a Peltier element and put wet rag on one side and big heat sink on the other side.
Water will be evaporating from the rag and it will be cooling.
This creates small (about one degree) temperature difference for several hours.
Using modern DC-DC converter for energy harvesting (like LTC3108) some small electronic device can be powered e.g. clock.
I also believe that it is possible build similar system with "closed cycle" where water (or perhaps some other coolant circulate inside device).
This, however, presents much more serious engineering challenge.
Energy-Harvesting-power-supply:
http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy (http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy)
Peltier modules
http://www.ebay.com/itm/TEC-12706-12V-40mm-X-40mm-X-3-75mm-Thermoelectric-Cooler-Cooling-Peltier-Plate-/262034289314?hash=item3d0275f2a2:g:yHEAAOSw0JpV6aWQ (http://www.ebay.com/itm/TEC-12706-12V-40mm-X-40mm-X-3-75mm-Thermoelectric-Cooler-Cooling-Peltier-Plate-/262034289314?hash=item3d0275f2a2:g:yHEAAOSw0JpV6aWQ)
No telling what this kid (https://www.youtube.com/watch?v=7WoNWslRx1g) will accomplish when his voice eventually changes.
Scary kid!