Undoubtedly you have seen many an instructable on how to make a larson scanner. There are also a lot of kits available out there too. I just made one from scrap parts, and I think it uses the fewest parts of any one I have seen.
Step 1: Parts
9 Leds, I had green ones on hand.
battery holder for 2xAA
Yeah, that is all I used.
Step 2: The Circuit
First things first, flash the tiny 2313 with the firmware provided by evilmad. Then assemble this circuit on a breadboard first. Then, once you have it working, transfer it to something more permanent, in this case perfboard.
I got my firmware from evilmad http://www.evilmadscientist.com/article.php/larsonkit
You could always make your own, but the one from evilmad is opensource, and has some nice pwm-ing on it... and I say if it aint broke, don't fix it.
Once you have the circuit working on a breadboard, and you understand how to wire it, move the leds to the perfboard. I spaced them out the way I wanted, and connected all the gnd pins across the top. When I clipped the gnd pins I save the leads, they are needed to extend some of the vcc pins on the leds, because some of them are too short to reach the tiny2313
Put the tiny2313 in the perfboard, pay close attention to the orientation of the chip, and wether you put it on the top of bottom of your target board.
I soldered the leds right to the pins if the tiny2313, the perf board to aligns the leds nice and flat. I used the chip orientation you see in the pictures to make it easier to solder it all together.
2AA batteries = 3V my leds can handle it, and I don't need any resistors.
Last just solder on the battery
Step 3: Video
Here it is working nicely.
Some additions would be to add a button, I believe the firmware supports changing the brightness of the leds, but this worked fine for me.
You could also solder in a socket for the chip, so the chip is less permanent, but that is an additional part.
Now go jam this baby in a pumpkin or something!
If you find the instructable is too difficult for you go buy a larson scanner kit from evilmad!!!