@bobricius could you please tell me more about the charging system? Do you have brown out disabled to maximise the runtime? If possible posting a png of the schematic would be great as I am stuck on a mobile phone with no EDA for a while. Is it just a resistor? How did you determine the charge rate? Thanks 

Hi, I randomly pick for charging only 4R7 ... nothing special, just usb and supercap. yes, brown out is disabled it consume about 20uA and between flashes is MCU in deep sleep with watchdog wake up, also when led is on is MCU in sleep to save power. With this setup can it flash hours and hours ...

Thank you. 

add solar panel and ... clock binary or normal.

very interestin project

Interesting concept, what is the advantage of using a supercapacitor instead of a battery?

unlimited life, fast charging, cheap, reliable, small ...

I thought the main disadvantage of supercaps is that they are expensive. 

I read they have issues with leakage current. Does this concern you?

Also, the discharge of a supercap is linear, so the voltage would likely drop below the level required to power the Atmel chip before it has discharged. Compared to lithium cells, which have a flat discharge rate, this seems disadvantageous.