How to make flip-flop (frequency-divider) with schmitt inverter?

[johnyradio]

Hi

Ideally, i'm looking for a simple frequency divider that i can feed a square wave, using only schmitt inverters or schmitt NAND (just one if possible). Should work over a wide input-frequency range.

The posts below provide a schematic for a so-called "flip-flop" (which i think is really a toggle, not a flip-flop) using two schmitt inverters.

https://www.electro-tech-online.com/threads/electronic-switch.26093/#post-181844
http://forums.adafruit.com/viewtopic.php?f=8&t=36970&p=607457#p607457
http://www.learningaboutelectronics.com/Articles/Touch-on-off-circuit-with-a-7414-inverter.php

The circuit is based on a switch, not a clock, so would not work as-is for my need. But, maybe someone can see a way to make this work as a divider with a clock-input instead of a switch? Or, some alternate flip-flop circuit using schmitts?

I wired up the above circuit in falstad
http://tinyurl.com/ya8cz2nm

Issues:

• Seems highly sensitive to input on-time.
• Getting strange oscillations.

Pressing the switch manually, i sort of get a toggle, sometimes. Seems to depend on how long i hold the switch, and maybe how long i wait between presses, and whether i'm going from low to high or high to low. Also, i seem to get a very high frequency oscillation while holding the switch. Am i doing something wrong?

Any ideas for a true flip-flop divider based on Schmitts?

thx

 

[crutschow]

It's difficult to use such a circuit over a wide frequency range since it depends upon RC delays for proper operation..
Much easier to just us a D-flipflop with the D input connected to the /Q output.

 

[ci139]

you could try something alike (but please don't use this simulator for complex circuitry - LT Spice is yet free)

 

[johnyradio]

you could try something alike

Thanks! but It says "convergence failed".
Where do i connect my square wave source?
Can you show the scopes? Cannot see the scope for some reason.

thx!

 

[ci139]

something #2 why to bother (it's not too reliable approach)
the mod2 doesn't cost a fortune / confirming non complex only simulator ► https://tinyurl.com/y8emsf53

 

[johnyradio]

many thanks, ci139
since no easy, wide-frequency way to do with schmitts, i'll go with a flip-flop chip.

thx!

 

[ci139]

no easy, wide-frequency way

you never know until you occasionally somewhere run to it - some setup of T-flop might just do what you need

by Google iS . . . the good question here is where to get the BUTTON with the right "Moment" . . . the 100k somewhat incorporates here . . . donno ← an idea level design (in latch setup the button would be the 3-rd transistor) while the Bjt v. has only 2

 

[schmitt trigger]

Cross coupled NAND or NOR gates also make a good SR flipflop

 

[crutschow]

Cross coupled NAND or NOR gates also make a good SR flipflop

But not as a toggle flipflop for a frequency divider as the TS wants.

 

[MikeMl]

Here is the simplest, "real", divide-by-2 circuit made from gates. It is properly edge-triggered, and changes on rising-edges. It can be built from almost any logic family, provided that the max frequency is consistent with the gate delays.

 

[ci139]

https://www.indiabix.com/electronics-circuits/tunnel-diode-relaxation-oscillator/
https://www.indiabix.com/_files/images/electronics-circuits/tunnel-diode-relaxation-oscillator.png
https://www.google.com/patents/US3109945
https://patentimages.storage.googleapis.com/pages/US3109945-0.png

 

[johnyradio]

confirming non complex only simulator ► https://tinyurl.com/y8emsf53

your sim here does not seem to divide. Just seeing flat lines on the scope.
thx!

 

[johnyradio]

Here is the simplest, "real", divide-by-2 circuit made from gates.

Wow, is that 6 NANDs?
Great!

 

[johnyradio]

https://www.indiabix.com/electronics-circuits/tunnel-diode-relaxation-oscillator/
https://www.indiabix.com/_files/images/electronics-circuits/tunnel-diode-relaxation-oscillator.png
https://www.google.com/patents/US3109945
https://patentimages.storage.googleapis.com/pages/US3109945-0.png

i'd just as soon go with a monolithic flip-flop chip. Fewer parts.
But if one of these used schmitts, then i'd be interested!