Discussion in 'The Projects Forum' started by jack mcleod, Dec 9, 2008.
How are three 4017s connected to give 24 consecutive outputs and then recycle?
A CD4017 is a decade counter. Two of them can count to 24. Possibly you mean something else by "24 consecutive outputs"?
What is required is 24 outputs that go high one after the other then recycle.
My limited knowledge has my first 4017 counting units but my second 4017 is counting 10,s and the first 4017 recycles rather than stopping. Help!
That won't work with 4017's. Each only has 4 outputs, and they are BDC coded. It sounds more like a shift register is more the thing than a counter.
Can you post a schematic?
Ahhh, 4017's are 5-stage Johnson counters; they have 10 outputs, only one of which is high at any given time.
When cascading 4017's, you need to use a couple of AND gates. The first 4017 will have 9 outputs, subsequent 4017's will have 8 outputs, for a total of 25 unique states.
See the attached schematic.
If you want it to recycle at 24 counts, on the rightmost 4017 move the Q9 output's connection to the Q8 output.
You could use 4011's for the AND gates. Make sure to tie any unused inputs to GND or VDD.
Neat! I'd been thinking in terms of one "master" mux/demux chip controlling others through the enable pin. This is much neater. Here is the datasheet for a 4017.
You're right. I peeked in my logic manual and saw "Decade Counter" and concluded another BCD counter like a 4029.
Thanks to all especially Sgt Wookie. The second part of this project will be posted under 4017's Part Two.
This is one of my favorite light chaser chippies. Here was the last one I helped with...