This circuit pulses an LED at an adjustable rate (set by capacitor size chosen and charging resistor) ranging from several Hz down to once every few minutes or so. The flashes are fairly bright and can be noticed from many yards away in slightly dim lighting.
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SMD Pulser No Boost Basic 5mm LED V2_2023-06-07.zip
Great Idea! I actually did that with a version of this circuit a year or so ago. That circuit used a solar cell from a calculator to charge supercapacitors during the day. It would last about 3 days after being charged in direct sunlight for ~30 minutes. Unfortunately I was never able to make the circuit operate by just using the solar panels to power the circuit directly using indoors ambient light, so I'll definitely be trying that next!
If you use blue or white LEDs they are much brighter but you'll have to use 3V cells because of the higher forward voltage.