Hi there - I want to make a device that blinks two LEDs both with 50% duty cycle and with a 180 degree offset to each other. They don't need to be super bright - 1-2ma I'd guess. I want it to run 24/7. It will be running inside and will be subjected to electric light during the day, and will be in the dark at night. I want the LEDs to run even when it isn't in the light. That means some sort of energy storage device.
I'm thinking a supercap for this: http://search.digikey.com/script...
So 100F at 2.7V gives me 364.5J (.5CV^2). So unless my maths are failing me - that means, if I'm pulling 1ma at 2V, I'd get about 50 hours run time ((364.5 W * seconds) / (2mW)) * (1 hour/3600 seconds), assuming perfect DC/DC efficiency. Of course I probably won't have have a DC/DC (unless somebody knows of one that would work well here - I'd just assume quiescent current would make one not practical). But still 50 hours is way more than I need. I really need only about 10 or so - so this seems reasonable.
Now for charging this capacitor - I was thinking I'd do something stupidly simple - diode in series with a solar panel (to prevent reverse current) connected across the leads of the capacitor. Zener diode across the leads of the capacitor to make sure it doesn't get overcharged. Or maybe is there a better way?
What do you all think?