I have a question about using NAND gates as an oscillator.
There is a circuit which uses invertors in place of NAND gates on this link:
The circuit on the top right of page 3 is identical to a circuit I saw in Nuts and Volts (the hobbiest magazine) a few months ago (except they used NAND gates). R1 was 10Mohm I believe and they said the frequency of the circuit is 1/(2.2RC).
If you look on page 2 on the same link as above, they use three invertors total, but have a huge formula.
My questions are:
Why did Nuts and Volts state the formula is 1/2.2RC, where did the 2.2 come from?
What is the R1 resistor (10Mohm) providing?
Why is the formula on page 2 so long (while Nuts and Volts had such a simple formula) and where do they get the two weird numbers: 0.405 and
0.693?
This is not a homework problem. I saw this circuit in Nuts and Volts, took the formulas for granted and now I'm curious and couldn't find much about the circuit.