Since this question in reality covers - General Electronics, Programming, Arduino... so i got thinking.... an LED chaser (old skool) the most basic of basic, would simply be a 555 hooked up to a 4017 and have however many pin outs it supports (8/9? off the top of my head)
So for a couple of bucks each, and a small breadboard, i may not be able to Multiplex or send Binary Data down the wire to say I want pin 5 on, but it does have the ability to encode/decode and count up to 8 or 9, now 3 outputs from arduino to 3 4017's, you could have 1 - 8 light up (in sequence) and then have the 2nd out to another 4017 and so on, you could quite easily get a giant chaser going ..
Anyone see anyone down sides to this? $2 vs $15-$20 a pop for something not too dissimilar if all you're after is an LED chaser or crystal timer outputting the time or something... maybe someone's already seen a thread like this already, but i've got quite a few left over IC's, Quad Comparators, OP-Amps, audio waveform (siren) generator, and a few other logic IC's all of which have been made a bit obsolete with Arduino and now i'm thinking of putting them to good use again..
3 4017s (9? outputs) 27 semi controllable sequenced LED's (for example, the first row could fire up and then have the 2nd pin fire on the 2nd pulse, the 3rd 4017 gets activated when the 3rd high/low signal gets sent) you could then speed each of them up or down, or have them flash in sequence, if you're going to be a little creative i'm sure you could do some quite impressive displays with a few simple 4017's sure you don't have the complexity of dedicated IO extender IC... but really is it justified?.. 8 4017's then multiplex them, send a pulse out to the 1st pin, 2nd pin, 3rd pin,... i think you get the point..
and if i remember correctly, 4017 has a decent amount of source current to...