This is another of my pictures originally posted to my warsonseblog in 2009. This uses a whole board full of 1F 2.5VDC super capacitors I got from an online surplus sales, I don’t remember which. I think they were all used since the leads were short. At that time I don’t believe that super caps bigger than 1 Farad were available, at least not for a reasonable price.
The Flashing JT uses a two transistor astable multivibrator circuit with assymetrical part values to make it stay off for much longer than half the time. The third transistor is the driver, which switches only the base current to the final Joule Thief transistor. This circuit uses more current than my Blue Blinky, but the flash is brighter due to the LED being on longer.
The solar cell is tiny and supplies only 20 mA on a really sunny day. This disappears into the 20 farads like a cup of water into an empty swimming pool. It takes quite a while for the bank of super caps to charge up.