Electronics Formulas
I'm going to try to keep some useful and practical formulas for electronics here. The goal will not be to have a million formulas, but to have the formulas that not so complex that you would rather use an online or spreadsheet calculator for them.
List
Todo: enable math extension.
Capacitor Discharge
You should memorize this, and know the rules of thumb for a 1uF w/1kOhm or 1MOhm. It is the easiest of all formulas, probably.
T=RC. Capacitors#Student_Manual_for_Art_of_Electronics_.28ver_2..29
High or Low Pass Filter
1 over 2πRC
If you know your resistor (i.e. use a standard value, say 10k, 100k) you can reverse calculate the desired capacitance easily. Some of these values can be more or less memorized if you do this enough, given that a 2πR with R being a factor of 10 will always be 2π to some decimal point. That leaves the capacitance as the only variable. Note this is for the 3db point, or about 70%, and you would might make this 2 * desired frequency per AoE, Student manual. Of course, this is basic algebra, and the formula is C=(1/2πR) * freq. I find this a bit more intuitive for some reason, as I usually know what frequency I want to block but do not know what capacitance to use.
THD from an Oscilloscope FFT function
To recap, in this video he has a DUT that he is checking how it changes the input from a function gen, by outputting to the FFT mode of the scope, counting the dBc between the first fundamental and each following harmonic, and then doing some math to calculate the result. He also compares the result to test equipment that has a THD mode. If you have a scope w/FFT and a DUT that you need to check the THD of (and the noise is simple enough) this video may help. Note that this is usable for fairly large THD values (though a dedicated THD analyzer, distortion analyzer, or spectrum analyzer may do better, that is left open to discussion). This is for only harmonic distortion.
