Need help with a cascaded 4017 sequencer circuit

[CremeDeMentia]

Hello everyone.  I've read posts here and there on this site, I've been bending stuff for about 3 years now.  This is my first post (that I remember, any way).   

I already posted this to a similar forum that I just joined, and I hope you don't mind me being a bit lame and posting the same message rather than retyping it:

Hi everyone!  I'm starting to work with ICs and I have an idea in mind that I need to get out of my head.

I've been working with 4017s and 555s to make a sequencer that will in turn cue sounds from a toy. I want (I think) a clock signal supplied by a 555 because I want to be able to adjust not only the frequency of the clock signal but also the *length* of the clock pulse. I want (I think) 4017's so that I can vary the number of steps in my sequence.

My original source for the circuit I came up with is:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm

specifically:



I used the cascaded 4017 18-stage sequencer circuit (above) to come up with this:



It cycles nicely through 16 steps. What I don't understand is what is going on with the logic gate created by the 1N914 diodes; I actually came up with this circuit just by playing with the one from the page I mentioned earlier, not through any math or innate understanding of ICs.

What I would like to do, but can't really figure out, is how to modify the circuit so that I can manually change the number of steps in the sequence. I'd like to be able to install maybe a rotary switch which would set the amount of steps in the sequence by connecting the necessary RESET pin to different pins from the 4017s . This would allow me to assemble and sequence patterns in different time signatures, but I don't know if it really works like that.

Is there a simpler way of cascading two 4017s?

Any body else out there working on similar sequencers?

Any comments, suggestions, questions, etc. are very welcome, this is uncharted territory
for me.

--Austin aka Creme Dementia
http://www.myspace.com/cremedementia

[superset]

Hey, this is my second post ever, and both are today... not that it matters but i have some thoughts for you.

First off... I haven't yet tested the below circuit.  I have built the sequencer portion and it works beautifully, but like you I need a counter to control the total steps in a sequencer.  Below is the design... although it uses a 4067N (16 channel multiplexer) the principle would be the same.

What I think you need to do is have another counter (4017) and instead of controlling it w/ a clock control the output with a manual momentary switch... each press of the button will up the counter by one holding the outputs at this value.  Next, use a comparator to compare the output of this counter to the position (total count) of your sequencer...  Then, route the output of the comparator to the 'reset' input on your sequencer 4017.  This way, when the voltage goes high on your comparator output (due to a match in values between the manual counter and sequencer counter) it should trigger the reset on the sequencer, starting over at 0.  in theory anyway.

I've added the schematic to what I've designed for myself to give you some ideas.  I plan on testing this soon... once I do I'll post again with some follow up feedback and ideas.

I hope this helps a bit

-Dave


...Just want to add another note... in my design I use 4 bit binary counters (4520) which when thinking of the signal flow you would substitute with your 4017s.  obviously you have no need for the 4067.

[Dj Task Manager]

has anyone tried and successfully got a darlington pair (flip flop) to alternately trigger two 4017's for more steps?
if so i'd like to see a schematic!

[Gordonjcp]

I don't know why you'd need a Darlington pair, the current needed to drive the 4017 is tiny.

[Dj Task Manager]

Like I said I was thinking of triggering two 4017s alternately from the two sides of the flip flop to get more steps...  
Perhaps though there is a more elegant approach...

[Gordonjcp]

Typically you'd use a Darlington pair to switch something drawing several amps at least.  The inputs to CMOS gates draw something in the region of nanoamps...

Somewhere at the start of this thread there is a circuit for a multi-step sequencer that cascades two 4017s.  It ought to be possible to extend it further.  It works, but you need to be careful about how you load the outputs.