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74HC74 oscillator simulation

Started by bitrex August 3, 2019
IRL I don't think there's anything this configuration of the 'HC74 could 
do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, 
and not-PRE grounded.

But with these models from the Yahoo LTSpice users group the LTSPice 
time domain looks like it manages to find some other metastable state 
and sits there spinning its wheels.

Can anyone suggest some ICs that could bust it out and get it to 
square-wave in the sim? Thanks

<https://imgur.com/a/Idv4LSs>
On 8/3/19 12:06 PM, bitrex wrote:
> IRL I don't think there's anything this configuration of the 'HC74 could > do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, > and not-PRE grounded. > > But with these models from the Yahoo LTSpice users group the LTSPice > time domain looks like it manages to find some other metastable state > and sits there spinning its wheels. > > Can anyone suggest some ICs that could bust it out and get it to > square-wave in the sim? Thanks > > <https://imgur.com/a/Idv4LSs>
plz use this link instead <https://imgur.com/a/ochGSav>
On 03/08/2019 17:06, bitrex wrote:
> IRL I don't think there's anything this configuration of the 'HC74 could > do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, > and not-PRE grounded. > > But with these models from the Yahoo LTSpice users group the LTSPice > time domain looks like it manages to find some other metastable state > and sits there spinning its wheels. > > Can anyone suggest some ICs that could bust it out and get it to > square-wave in the sim? Thanks > > <https://imgur.com/a/Idv4LSs>
74HC132 or if you just want simplest then 74HC14
On Saturday, August 3, 2019 at 12:06:10 PM UTC-4, bitrex wrote:
> IRL I don't think there's anything this configuration of the 'HC74 could > do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, > and not-PRE grounded. > > But with these models from the Yahoo LTSpice users group the LTSPice > time domain looks like it manages to find some other metastable state > and sits there spinning its wheels. > > Can anyone suggest some ICs that could bust it out and get it to > square-wave in the sim? Thanks > > <https://imgur.com/a/Idv4LSs>
Are we supposed to know what the two traces are in the circuit? If they are the two ends of the resistor, there is something wrong. I expect it is the model of the FF. Perhaps the model is not gate accurate. Try driving the CLR- input from a square wave and see if the Q- is inverted from that. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
On Sat, 3 Aug 2019 12:06:05 -0400, bitrex <user@example.net> wrote:

>IRL I don't think there's anything this configuration of the 'HC74 could >do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, >and not-PRE grounded. > >But with these models from the Yahoo LTSpice users group the LTSPice >time domain looks like it manages to find some other metastable state >and sits there spinning its wheels. > >Can anyone suggest some ICs that could bust it out and get it to >square-wave in the sim? Thanks > ><https://imgur.com/a/Idv4LSs>
The voltage gain from \Q to \CLR is low, and there's no schmitt action, so you can get a stable negative feedback loop. It would likely oscillate at a higher frequency, where the logic prop delay becomes important. Why not use a schmitt inverter? This circuit could be rescued, but it would take more parts. Maybe "ground" C1 to Q? But I wouldn't trust the Spice models for what is basically analog behavior. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 8/3/19 12:19 PM, Rick C wrote:
> On Saturday, August 3, 2019 at 12:06:10 PM UTC-4, bitrex wrote: >> IRL I don't think there's anything this configuration of the 'HC74 could >> do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, >> and not-PRE grounded. >> >> But with these models from the Yahoo LTSpice users group the LTSPice >> time domain looks like it manages to find some other metastable state >> and sits there spinning its wheels. >> >> Can anyone suggest some ICs that could bust it out and get it to >> square-wave in the sim? Thanks >> >> <https://imgur.com/a/Idv4LSs> > > Are we supposed to know what the two traces are in the circuit? > > If they are the two ends of the resistor, there is something wrong. I expect it is the model of the FF. Perhaps the model is not gate accurate. Try driving the CLR- input from a square wave and see if the Q- is inverted from that. >
I noticed just now I made a mistake setting up the sim, when using these digital models one is supposed to set the line: SpiceModel: VCC 0 at 0 not VCC 5 as I had it. and VCC=5 SPEED=1.0 TRIPDT=1e-9 for SpiceLine. Not super intuitive but is what it is I guess I don't use the digital models often. No guarantee it will fix this particular situation but it should make the models actually, like, work in general
On 8/3/19 12:24 PM, John Larkin wrote:
> On Sat, 3 Aug 2019 12:06:05 -0400, bitrex <user@example.net> wrote: > >> IRL I don't think there's anything this configuration of the 'HC74 could >> do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, >> and not-PRE grounded. >> >> But with these models from the Yahoo LTSpice users group the LTSPice >> time domain looks like it manages to find some other metastable state >> and sits there spinning its wheels. >> >> Can anyone suggest some ICs that could bust it out and get it to >> square-wave in the sim? Thanks >> >> <https://imgur.com/a/Idv4LSs> > > The voltage gain from \Q to \CLR is low, and there's no schmitt > action, so you can get a stable negative feedback loop. It would > likely oscillate at a higher frequency, where the logic prop delay > becomes important. > > Why not use a schmitt inverter? This circuit could be rescued, but it > would take more parts. > > Maybe "ground" C1 to Q? > > But I wouldn't trust the Spice models for what is basically analog > behavior. > >
Check this out someone actually got a patent for this back in 1990 (the crystal probably helps a lot): <https://imgur.com/a/YryI2p6> I noticed just now I made a mistake setting up the sim, when using these digital models one is supposed to set the line: SpiceModel: VCC 0 at 0 not VCC 5 as I had it. and VCC=5 SPEED=1.0 TRIPDT=1e-9 for SpiceLine. Not super intuitive but is what it is I guess I don't use the digital models often. No guarantee it will fix this particular situation but it should make the models actually, like, work in general
On Sat, 03 Aug 2019 09:24:40 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Sat, 3 Aug 2019 12:06:05 -0400, bitrex <user@example.net> wrote: > >>IRL I don't think there's anything this configuration of the 'HC74 could >>do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, >>and not-PRE grounded. >> >>But with these models from the Yahoo LTSpice users group the LTSPice >>time domain looks like it manages to find some other metastable state >>and sits there spinning its wheels. >> >>Can anyone suggest some ICs that could bust it out and get it to >>square-wave in the sim? Thanks >> >><https://imgur.com/a/Idv4LSs> > >The voltage gain from \Q to \CLR is low,
Actually meant \CLR to \Q, the gain inside the IC. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 8/3/19 12:59 PM, John Larkin wrote:
> On Sat, 03 Aug 2019 09:24:40 -0700, John Larkin > <jjlarkin@highlandtechnology.com> wrote: > >> On Sat, 3 Aug 2019 12:06:05 -0400, bitrex <user@example.net> wrote: >> >>> IRL I don't think there's anything this configuration of the 'HC74 could >>> do but oscillate; with an RC network from not-Q to not-CLR and D, CLK, >>> and not-PRE grounded. >>> >>> But with these models from the Yahoo LTSpice users group the LTSPice >>> time domain looks like it manages to find some other metastable state >>> and sits there spinning its wheels. >>> >>> Can anyone suggest some ICs that could bust it out and get it to >>> square-wave in the sim? Thanks >>> >>> <https://imgur.com/a/Idv4LSs> >> >> The voltage gain from \Q to \CLR is low, > > Actually meant \CLR to \Q, the gain inside the IC. > >
The easy thing to do to get a square wave is the schmitt inverter, I'd like a low frequency (10s of Hz) with the Q and not Q outputs but I don't wanna use a large R, large cap, wanna use a small R and cap that's relatively cheap to get tight tolerance/tempco on the components. The easy thing to then do is run a higher frequency from the standard schmitt inverter with smaller Rc, C into a divider chain. But it would be cool if there were some self-oscillating structure of flops that did it all without needing the Schmitt inverter at all, so far my attempts to find it have been unproductive though If you have Q and not Q whether from a flip-flop or just from a set of appropriately-connected inverters it might be possible to bootstrap the RC constant capacitor somehow instead of grounding it.
On 03/08/2019 5:08 pm, bitrex wrote:
> On 8/3/19 12:06 PM, bitrex wrote: >> IRL I don't think there's anything this configuration of the 'HC74 >> could do but oscillate; with an RC network from not-Q to not-CLR and >> D, CLK, and not-PRE grounded. >> >> But with these models from the Yahoo LTSpice users group the LTSPice >> time domain looks like it manages to find some other metastable state >> and sits there spinning its wheels. >> >> Can anyone suggest some ICs that could bust it out and get it to >> square-wave in the sim? Thanks >> >> <https://imgur.com/a/Idv4LSs> > > plz use this link instead > > <https://imgur.com/a/ochGSav>
Way back when I did get CMOS 4013A to oscillate sucessfully. I seem to remember it needed 2 caps and 2 Rs though. Was fine until the buffered series 4013B took hold and 4013A became hard to get. The extra internal buffer stages refused to play such dirty tricks. piglet