Electronics > Beginners

Not understanding behaviour of HCF4093BE: Schmitt Trigger NAND gates

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wraper:

--- Quote ---It looks like their individual frequency is changing with time.
--- End quote ---
Of course frequency drifts by certain degree. However it has nothing to do with what you are observing. Your brain is just fooling you. Remove any 3 LEDs at a time and observe that each separate LED blinks at stable pace. Or just cover them with something non transparent if you are not convinced.

javi14:

--- Quote from: wraper on January 05, 2020, 08:25:59 pm ---
--- Quote from: javi14 on January 05, 2020, 08:17:47 pm ---
--- Quote from: wraper on January 05, 2020, 05:28:14 pm ---Electrolytic caps usually are rated for +/-20%, IC input threshold voltages are not quite precise too.

--- End quote ---

So, is it possible that each NAND input has a different threshold voltage? I understand that this would make my circuit useless, as I wouldn't be able to control the LEDs precisely.

But, what still bothers me, is that the LEDs are not oscillating at a fixed frequency (each of them, separated frequencies). It looks like their individual frequency is changing with time.  So my question is now, is it possible that the threshold voltage of the NAND inputs changes every oscillation period?

Thank you for your help, I really appreciate it.

--- End quote ---
I don't know why you want separate oscillators to begin with. If you want LEDs blinking synchronously, you need single oscillator. Even if you use super precise oscillators, they will go out of sync eventually. If you want to disable certain LEDs, you do it after oscillator, not create bunch of oscillators.

--- End quote ---

So I will disable/enable them after oscillation. Using a single oscillator. It is definitely a better idea. Now I need to figure out the circuit to do it.
Thank you for your detailed responses!
This topic can be closed now.

james_s:
Ah, I thought the goal was to have them individually flashing out of sync was the goal, otherwise yeah use one oscillator and then use the other gates to individually enable the LEDs you want to flash.

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