[sdiy] Funky flip-flops

[harrybissell]

Yes Jay...

I'd like to add... decoupling caps. TTL is desperately in need of good power supply
decoupling.   I'd suggest a .1uF cap across EVERY single TTL chip.   I follow this rule even
with 4000 series CMOS... which could use probably half that amount.

About the RC on the ... clock line ??   I would not use a filter on the clock line... TTL needs
a good fast pulse to trigger well... although I have seen some times where a tiny tiny RC
helps in stopping a bounce (and mistrigger).  Better to fix the real problem than try to mask
it.

A modest proposal... switch to 4000 series CMOS.  It is way, way, way easier to use than TTL,
uses a fraction of the power...

...unless the TTL stuff was free, of course...

H^) harry

jays at aracnet.com wrote:

> Reset sounds funky.
>
> 1) Holding the reset lines low has the FF in a constant state of reset. They are active low and should be tied high (reset to +V) with a 1K-3K ish resistor. Or better yet put a cap in there between reset and ground (with the resistor in there) to form a RC that slowly charges up to V+ providing a power on reset. Also if you aren't using the resets individually you should just tie them altogether.
>
> If I were to guess I'd say there might be some interaction between the PS and the 10K reset resistors not providing a 'weak ground'.
>
> 2) If you tie stuff to ground don't use a resistor.
>
> 3) Put some sort of RC on the switches going to CP.
>
> 4) Put a pull up (1K-2K) on the ~set lines. It's active low to.
>
> Jay S.
>
> Karl Ekdahl <_nial_ at yahoo.com> wrote :
>
> > Hi all, i've got a strange problem. I have 8
> > flip-flops (4 * 7474) which all share a common ~SET
> > line and each have it's ~RESET tied to ground trough a
> > 10k resistor. Each flip-flop is connected to itself
> > via ~Q -> D and each is set/reset trough a push button
> > connected to CP. All Qs are connected to one LED each.
> > So, pushing the first button sets/resets the first
> > flip-flop. Pushing the 8th button while the first
> > flip-flop is set resets the FIRST one and sets the 8th
> > one. Pushing the 8th resets the 8th flip-flop and then
> > pressing the 1st sets BOTH flip-flops. All the
> > flip-flops reacts like this with eachother in all
> > kinds of strange patterns. The only way they possibly
> > COULD interact with eachother should as i understand
> > it be
> >
> > a) the comon SET
> > b) trough the RESET resistors to ground (?)
> > c) trough the 74245 that delivers the signals from the
> > pushbuttons.
> > d) powersupply noise (?)
> >
> > a) could probably be ruled out since they bot SET and
> > RESET eachother. b) and d) is the same i guess and i
> > have a pretty huge powersupply feeding only a couple
> > of TTL chips, so that seems unlikley. I had
> > powersupply problems earlier but fixed that. c) the
> > 74245 seems to give perfect result while looking at it
> > with my multimeter, so i don't think so...
> >
> > I'm stranded, anyone?
> >
> > btw. i might as well thank everyone for their help
> > with various things the last couple of weeks, i'll put
> > some pictures and stuff of what i'm doing somewhere in
> > some time..
> >
> > Karl