[sdiy] Funky flip-flops

[harrybissell]

They even made SOCKETS with the decoupling cap tied right to the power pins... so that
the inductance was at a minimum... and of course it saved a lot of board space without
one cap per IC...

otoh JIM PATCHELL seems to have no problem fitting in one cap per power supply pin
per chip.  GO JIM !!!

(I do the same :^)

H^) harry   (I'm not just the president of capacitor club for diy'ers... I'm also a member)

Scott Gravenhorst wrote:

> harrybissell <harrybissell at prodigy.net> wrote:
> >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.
>
> This was the configuration of DEC mini-computer boards, though I can't remember what the cap value
> was.  It was all made with TTL of one flavor or another, and each IC was bypassed.
>
> >I follow this rule even with 4000 series CMOS... which could use
> >probably half that amount.
>
> I second this.
>
> >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
> >
>
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