I tried building my own ring oscillator on a breadboard and ran into some issues. After several failed designs (mostly using 2 inverters - insipired by the CD4060 oscillator), I tried to go simple and go with a classic 3 gate design as shown.
I figured based on that circuit that I could use TTL inverters (74 HC 04) with equal resistors and capacitors (R = 1 k ohms, C = 1 micro farads) and then buffering the output in order to see some oscillation (I was aiming for low frequency, around 1 Hz).
I built the following circuit which did not oscillate. I measured the voltage across the capacitors whilst trying to debug the circuit and it was around 1.8 V constantly, across all three capacitors (5V supply voltage).
Finally, after some more googling, I happened upon this Ring oscillators which described the following circuit, using the same 74 HC 04 IC that I used.
Due to a lack of available parts I replaced the 4,7 Mohm resistors with 1 Mohm ones and the 100 nanoF capacitor with a 10 nF capacitor and I could see oscillation, the circuit did indeed work as advertised.
So my questions are why did the first circuit not work? What was wrong with it? What made the second one work? And how do you calculate the frequency of such an oscillator? Do the capacitors not being non-polarized have something to do with it?