Are you looking for a circuit that lets you flash or drive an LED from a single battery? This article from EDN has just what youre looking for:
Simplified white-LED flasher operates from one cell .
Heres some of the highlights of this clever design:
Uses a low-voltage logic gate to allow one-cell operation uses an inductor whose value is not critical operating voltage ranges from 0.8V to 3.6V, so even somewhat spent batteries can run it can be converted to non-flasher by omitting components low Parts count includes stuff you probably already have in the junk drawer
Back in the day, the LM3909 used to be a popular, simple solution, but its discontinued (although you can scrounge old stock occasionally)
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