Thanks for that. I've moved the chips around a bit, but still no luck.
I may have a go at building the circuit on some perfboard to see if
that makes a difference. All depends on available time!
Thanks again for the explanation.
--- In firstname.lastname@example.org, "wilf_nv" <wrigter@...> wrote:
> Hi Jo,
> Probably only occurs on the bread board with the larger stray
> capacitance between contacts.
> The second resistor in series with the inverter input together with
> the stray input capcitance acts like a small RC filter that can slow
> the rise and fall times of the input waveform long enough to permit
> double transitions in the output waveform during switching. These
> double transistions are divided by the FF with the result that the
> FF output seems to follow the clock input.
> Lowering the value of the series resistor to the minimum that will
> still generate 50% dutycycle, will reduce the likelyhood of the
> double transitions
> Another way to test if this is a breadboard issue is to use a
> different layout of inverters with corresponding different stray
> capacitive coupling.