3 LED flasher circuit

[Firefly]

I need a circuit to flash 3 LED's such that:

1. LED 1 comes on
2. About 1/2 second later, LED 2 comes on and LED 1 is still on
3. About 1/2 second later, LED 3 comes on and LED 1 and LED 2 are still on
4. About 1/2 second later, all LED's go off and the cycle starts over.

Could someone please point me to such a circuit or give me some idea of the chips (ie.555's?) and stategy I could try. Thanks in advance.

(Excellent board, by the way)

 

[bogdanfirst]

you can do this with a simple 4017 counter with some diodes and a pulse generator(like 555).
connect the first led with 3 diodes to the first, second and third outputs(use a transistor to drive the leds)
the second led connects to second and third output.
the third led only to the third output.
now, to the reset you can conect the 5th or whaterer output acording to the timing you want. i don't have thime to draw a schematic right now, and i hope you understand.
you need a 2Hz time base.