redoing some electronics

[Dovaka]

im trying to make a demultiplexer after looking around i found a schematic for it but it only uses 6 leds i want to try t omake one with 16-20 leds here is a very badly drawn version of the original http://draknet.com/wicca/dovaka/work/flasher.gif if anyone can help me out that would be awesome also if anyone knows of a cheap schematic program the only ones i can find are very expensive

[Graham]

Dovaka,
You can cascade the 4017 chips, the diag you have there could use 10 led's, just put one from each of the pins along the bottom row to the 0V line. As drawn the leds in the middle of the sequence will be on for two cycles, and those attached to pins 1 & 3 will be on for only one cycle, if this is not important then you can do as I said above to get ten.
Off the top of my head I cant tell you how to cascade two or more 4017's, but it is a simple job.
I will do some searching.

G

[randy48]

OK so what does a demultiplexer do?

[Graham]

Dovaka
Try http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm http://www.eleinmec.freeserve.co.uk/issue8.htm#art1

for some more info.

G

[Dovaka]

its the flashing red light in the front of the knight rider car

[randy48]

Check this out, it's a LED Chaser kit from All Electronics, 10-lights, $6.50. Good place to shop, good service/shipping!
http://www.allelectronics.com/cgi-local/SoftCart.exe/online-store/scstore/p-AEC.html?L+scstore+mqvz8348ff4c7f4c+979279699

[Graham]

Dovaka & Randy48,
What is described here is not a demultiplexor, you might call it a sequencer, or even a flasher, but not a demultiplexor.

G

[Dovaka]

well after digging thru about 10,000 notebooks i found this http://draknet.com/wicca/dovaka/work/Dscf0018.jpg i dont remember where i got it from it uses 16 leds but now i have a new problem the chip in the middle of the bottom diagram #74LS193 i can not find anywhere luckily i managed to take a pic of this one it would of taken me forever to draw it out

[Graham]

Looked at my usual suppliers (UK), no joy, searched though my 74 series draw, no joy, did a google search, first link
http://www.web-tronics.com/ls193.html

G

[Dovaka]

i actually found some at a place called mouser.com but they had discountinuded them and only had 10 left that werent even in the catalog but they want i thik 4 bucks for them

[Roy]

I'm not sure, but I think there is a 556 timer that has two outputs that alternate. These could trigger two 4017s to give you 20 sequential outputs. I guess you would have to stagger them if you want a 20 LED chase effect.

Or, you could take outputs 1 and 6 from the first 2017 and trigger two more 2017s. I'm not sure how the resulting outputs would time out.

Or, you could find a shift register that has 20 outputs instead of 10 ...