[sdiy] trouble driving cmos from modular signals

[Colin Hinz]

On Fri, 14 Sep 2012, Ullrich Peter wrote:

> Hi!
>
> The problem with the 4017 could be that not the levels are the
> problem but the signal edges. The 4017 needs fast edges to work
> properly. Slow rising signals will not work.
>
> So a Schmitt trigger on the clock input could be necessary.
> Something like a 40106 (Schmitt trigger inverter) - use two if
> non inverting is needed.
>
> Ciao
> Peter

This.

Edge-driven logic requires, quirkily enough, a nice sharp well-defined
edge in order to function. Often, the datasheet will be kind enough
to define what "sharp" means in terms of a risetime parameter.

- Colin