Expanding a simple Hex Schmitt Trigger LED Circuit

[Improviser]

schmidt trigger led

I am having trouble getting this to work with two stages, using one stage (3 LEDs) it works fine:

 

[betwixt]

hex schmitt trigger

The 1.0nF capacitor on the left side seems suspicious to me. If the circuit is supposed to work as a ring oscillator the 100nF capacitors between the gate inputs to ground have to charge in sequence but their only current source is via that 1nF capacitor. I would have used something much bigger or shorted it out altogether.

Brian.

 

[mfarooq1]

schmitt trigger

Simulate in Orcad or any other simulator you will find the solution

 

[Improviser]

hex smitt trigger

The 1.0nF capacitor on the left side seems suspicious to me. If the circuit is supposed to work as a ring oscillator the 100nF capacitors between the gate inputs to ground have to charge in sequence but their only current source is via that 1nF capacitor. I would have used something much bigger or shorted it out altogether.

Brian.

The circuit works fine with one 4584 and 3 LEDs but simply adding a second 4584 causes it to fail.

I have used bigger values in place of the 1nf with the same result. I will have to try it on Orcad, I am missing something obvious I am sure.

 

[betwixt]

simple schmitt trigger

Perhaps there is a clue in your reply.
I could be wrong and I'm not able to run simulations at the moment but the obvious difference is in the number of inverter stages. You say it works with 3 stages but fails with 6, can you try taking the feedback resistor from pin 9 instead of pin 4 of the second IC. You may not be getting feedback because the signal needs an odd number of inversions and you are giving it an even number. If it works with the resistor on pin 9, you can add a further inverter, maybe nothing more than a transistor, in the feedback path to get it running with still have 6 LEDs.

Brian.

 

[Improviser]

schmitt 4584 oscillator

That was a good idea. I am also unable to simulate it here.

 

[Audioguru]

simple schmitt

Why is there no schematic here?