This spiffy little gum stick sized circuit flashes a LED every couple of seconds. Powered by a small solar cell which charges a super capacitor, it can blink for ~36 hours in total darkness when fully charged. Ambient room light during the day seems to be enough to keep it going through out the night. I also have one powered by an AA battery which has been blinking since March of 2015 with no signs of slowing down.
P1: A small solar cell with 4 elements such as like you would find in a hand held calculator. It should have an output of about 2 volts or so.
C1: A one farad super capacitor
C2: 200 nano farad capacitor
C3: 100 micro farad capacitor
R1,3: 1 million ohm resistor
R2: 20 million ohm resistor (two 10 million ohm resistors in series in my flashers)
R4: 1 thousand ohm resistor
R5: 100 thousand ohm resistor
R6,7: 33 thousand ohm resistor
R8: 220 ohm resistor
T1,2: Small NPN switching transistor (example: 2N3904 or 2N2222)
T3: Small PNP switching transistor (example: 2N3906)
L1: Light Emitting Diode aka LED. A LED with a forward voltage of up to about 2.5 volts can be used. In my flashers, a high output green LED is used. Note that some green, blue, or white LEDs may exceed that so be sure to test your LED first.
P1 and C1 can be substituted with a 1.5 volt battery if desired.
The blink rate can be changed by varying R2 and/or C2. I suggest experimenting with this circuit on a breadboard to see what you like before making anything permanent.
Other Blinky Links:
Still going strong after nearly twenty years, this blinky in part inspired me to make mine.