[sdiy] Funky flip-flops

[Scott Gravenhorst]

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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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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