4017 IC with Arduino.

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...

http://www.youtube.com/watch?v=kyXzn5gb1Wg

now imagine controlling 8 4017's :D

The 4017 is a counter AND a (10pin) decoder, intimately connected internally. If you wanted to drive 2^n LEDs (one at a time) from n pins on an Arduino, you just need the "decoder" part, like a 74hc45 (10 outputs from 4 bits) or a 75hc138 (8 outputs from 3 bits)

If all you want is a giant chaser, you can cascade 4017-style chips together without any arduino, but it's somewhat limited in its flexibility.

Or the other way, an Arduino can "somewhat easily" make a chaser with 182 LEDs (14x13 array using "charlieplexing") with no additional chips at all. With full control over the pattern, etc... (and then you can take it apart and do something else.)

If you're willing to build your own board, the "Arduino guts" are about $5, rather than $15-20. Or closer to $3 if you're willing to go back in time and use an ATmega8...

The 4017 is pure nostalgia to me - a long long time ago I built a 6-decade counter using 4017's and ten LEDs per decade (rather like a dekatron circuit!) - it could run as a timer (using discrete 1MHz CMOS Xtal oscillator circuit) and possibly a frequency counter as well. In those days LEDs were not bright at all (not visible in daylight when driven from 4017's). IIRC the 4017 has an interestingly random pinout and interestingly random state on power up (more than one output active).