[sdiy] Funky flip-flops

[Karl Ekdahl]

I changed to 40 series logic (+ a few 74LSs) and it
all works great! didn't go down THAT much in
powerconsumption but enough! Thanks a LOT all of you
who helped me, now maybe i'll get this damn
drummachine working before i leave the country (i've
got one week)..

/Karl

 --- Harry Bissell Jr <harrybissell at prodigy.net>
skrev: 
> You can interface 4000 series with TTL but it has
> some problems.  The 4000 series threshold is about
> 1/2
> Vdd (or 2.5V).   TTL levels are less than .8V for
> low... and greater than 2.4V for high.  The 2.4V and
> 2.5V are close enough that it might be marginal.
> 
> There are some good 4000 series datasheets (app
> notes)
> that deal with interfacing CMOS. In general TTL can
> drive CMOS, but might need a pullup resistor. CMOS
> may not have enough current drive to reach the low
> TTL
> threshold... requiring a buffer.
> 
> 74HCT COMS is 'ttl' compatible for threshold... but
> still lacks the big current needed to drive TTL.
> 
> H^) harry
> 
> 
> --- Karl Ekdahl <_nial_ at yahoo.com> wrote:
> 
> > All in all i counted on 28 TTLs for three boards,
> > about 8 on the first one and the rest on the
> second
> > one. Anyhow i desoldered some of them yesterday,
> to
> > make room for CMOS instead. I noticed that i did
> > have
> > 40xx replacements for most parts, and a few LS
> > replacements will be made as well. Roughly
> counting
> > power dissipation i'm going from 230mW to
> 12mW.....
> > 
> > Oh btw, is it safe to mix 74LSxx with 40xx? I'm
> > still
> > going to run it on 5v in that case of course....
> > 
> > Karl
> > 
> > 
> >  --- harrybissell <harrybissell at prodigy.net>
> skrev: 
> > > If you have an output shorted to an output...
> the
> > > internal resistance
> > > of the devices is in the circuit. It will get
> hot
> > > but might not draw the
> > > huge
> > > current you are describing...  just more than
> > > normal.
> > > 
> > > How many chips on each board ?
> > > 
> > > H^) harry
> > > 
> > > Karl Ekdahl wrote:
> > > 
> > > > I looked for shorts and outputs going directly
> > to
> > > VCC
> > > > or GND but didn't find anything. I thought
> that
> > if
> > > any
> > > > of the two boards i'm making (it will be 3
> > boards
> > > > eventually) is having some kind of
> short-circuit
> > > or
> > > > likewise, it should draw a tremendous amount
> of
> > > power
> > > > so i measuerd the mA usage of each board.
> > > Apparently
> > > > the 3 x 2 digit LED displays draw 30mA
> together,
> > > the
> > > > first board around 220mA and the second 210mA,
> > > does
> > > > this sounds reasonable? If so, i guess this
> baby
> > > will
> > > > draw around 1A when i'm done, thus i can
> totally
> > > > forget of making this one battery operated as
> my
> > > first
> > > > thought was. Maybe i should just drop this and
> > do
> > > it
> > > > in PIC, though then i won't get rid of any 74
> > > chips.
> > > >
> > > > Karl
> > > >
> > > >  --- harrybissell <harrybissell at prodigy.net>
> > > skrev:
> > > > > Whenever something happens with a scope it
> is
> > a
> > > > > clue.
> > > > > I'd say there is no way the scope should
> knock
> > > out
> > > > > your
> > > > > power supply.  I'd suspect that you have the
> > > scope
> > > > > connected
> > > > > to ground (third pin if you're USA - are you
> > > ?)...
> > > > > and when you
> > > > > hook up the scope ground you are making an
> > > unwanted
> > > > > connection ?
> > > > > Or maybe the scope is mistakenly a 50ohm
> input
> > > (rare
> > > > > but possible) ?
> > > > >
> > > > > LEDs can eat amazing current... you can
> > > calculate
> > > > > from the series
> > > > > resistor, the power supply voltage and
> figure
> > a
> > > 1.5V
> > > > > drop in the
> > > > > LED. Three seven segment displays could be
> > more
> > > than
> > > > > 200mA
> > > > > alone.
> > > > >
> > > > > I'd look into that scope thing carefully...
> > > > >
> > > > > H^) harry
> > > > >
> > > > > Karl Ekdahl wrote:
> > > > >
> > > > > > So, i did add the 0.1uF decoupling caps
> and
> > > fired
> > > > > the
> > > > > > circuit, unfortuanley it behaved even more
> > > strange
> > > > > > than before so i tried plugging in my
> scope
> > > > > looking
> > > > > > for noise in the powerlines. Even more
> > > unfortunate
> > > > > is
> > > > > > the fact that every time i plug in my
> scope
> > > (an
> > > > > old
> > > > > > Tek scope) the fuse in my powersupply
> > brakes.
> > > > > > Apparently, the 74xxx does draw a lot of
> > > current,
> > > > > but
> > > > > > is it really so that a couple of 15 74xx's
> +
> > 3
> > > LED
> > > > > > displays should blow a 500mA fuse? It's
> > > becoming
> > > > > clear
> > > > > > to me that i have NO idea whatsoever how
> > much
> > > > > current
> > > > > > things actually draw. And by the way, yes,
> > the
> > > > > 74xxx's
> > > > > > are free - i've got shitloads and i want
> to
> > > get
> > > > > rid of
> > > > > > them so i decided to build an
> > overcomplicated
> > > > > > drummachine sequencer. I've also been
> > thinking
> > > of
> > > > > > building a *huge* pocket calculator only
> > using
> > > > > simple
> > > > > > logic 74xxxx's.
> > > > > >
> > > > > > Karl
> > > > > >
> > > > > >  --- harrybissell
> <harrybissell at prodigy.net>
> > > > > skrev:
> > > > > > > Yes Jay...
> > > > > > >
> > > > > > > I'd like to add... decoupling caps. TTL
> is
> > > > > > > desperately in need of good power supply
> 
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