My REAL question is how to choose the right components if you want a specific frequency spit out from a 555. In my particular case I want a potentiometer to control an output frequency from 16Hz to 33000Hz (roughly the tones audible to humans), and need to know the values of all the other components in the circuit.
I was perusing Forest Mims' Engineer's Mini-Notebook V2, and came across the following adjustable frequency tone generator. The image export is a little wonky, but it's readable. If you've got the book handy, it's on page 60.
What caught my eye was the formula and given table of values. Looking at the values, they just didn't seem to make sense, and I cannot get that formula to make any sense on paper given the components in the schematic. Using the 555 calculator, I can't make the math match the table either. It appears, however, that with a 4.7ohm resistor as R2, a 0.1uF cap for C1, a 100k-470ohm pot will deliver a range from 14 to 30037Hz. to
I'm trying to understand what I'm missing. If it's a simple "the book is waaaay wrong", fine...but I ALSO want to make sure I understand the math for the future.
My understanding of the formula is that R1 is my potentiomer, in Ohms. R2 is a non-variable resistor, also in ohms. But which cap of the two gets plugged in to the formula? do I total the caps? and what unit of measure is used in the formula? uF? pF? nF? F?
Is the info in the book bad? Are the numbers I came up with by playing with the calculator a better guesstimate of component values? Or is there something else I'm missing?