[sdiy] Funky flip-flops

[Tim Ressel]

Karl,

I'm assuming when you say 7474 you don't mean 74LS74
or 74HC74. The old TTL pulled lots of current, and
induced glitches on clock and reset line was a
problem. 

Step 1: Place 0.1uF caps across +5V and GND on each
IC.
Step 2: Test...
(if fails)
Step 3: Place 100pF caps on the suspect lines (set,
reset, etc) to GND. This should stop glitches.

If still fails, I'll have to see a schematic to dig
deeper.

--TimR

--- 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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