Turn the coil into a bifilar, or trifilar, so you can re-coup the B-EMF, as in a Joule Thief, in order to charge the same, or another battery. Using an LM-7805, and a TP-4056, you can do it. Use a Lithium-Ion battery.
my ,it s works since one year with AAA battery , selfstart ciruit ,ironless , like endless clock , and on top is a weight for agjust lower tact and hope for two years ,also there is build in a led in the pendel stick clouped with copper feders , but extra battery , you have a beautiful channel
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