And I think it's about it.
Knowing the voltage drops in LEDs to calculate the current going through a LED is also good to know, but I mostly don't care and go for a 1k resistor with 5V.
Can't think of any more formulas for small electronics, since all the other more complicated deride from these. :\
1/ (2pi Sqrt(LC)) - is the resonant frequency of an LC circuit
1/ (2pi FC) - is the capacitive reactance (equivalent resistance) of a capacitor at a frequency F. Replace C with L for inductive reactance.
See filter discussions in:- http://www.thebox.myzen.co.uk/Tutorial/PWM.html
When I went to tech school here in Phoenix, one of the things we were given as a part of our toolkit was (IIRC) a small folding "booklet" of equations for electronics, from - once again going from memory here - Graymark. I'll have to dig it up when I get home tonight...
Then there is:-
Q = VC
Where Q is charge in coulombs, V is voltage and C is capacitance (in Farads)
One coulomb is the amount of charge that flows past a point in 1 second when the current is 1 Amp.
1/ (2pi FC) - is the capacitive reactance (equivalent resistance) of a capacitor at a frequency F. Replace C with L for inductive reactance.
Small typo there, so just for completness sake: For inductive reactance the formula is the reciprocal (with regards to capacative reactance); XL = 2pi FL.
Since nobody have mentioned it, calculating resistance of resistors in parallel is also handy:
R = R1*R2/(R1+R2)
Personally I never use the above form, I like the reciprocals variant as it is simpler with more than 2 resistors:
1/R = 1/R1 + 1/R2 ... + 1/Rn
Same goes for capacitors in series btw:
1/C = 1/C1 + 1/C2 ... + 1/Cn
While capacitors in parallel just adds up (like resistors in series, so they are kind of opposite)
C = C1 + C2 ... +Cn
As I see it this requires at least 6 keystrokes over and above whatever it takes to enter the resistor values.
With RPN you enter:
R1, 1/x, R2, 1/x, +, 1/x
Since there is a 1/x key this gives you 4 keystrokes over and above whatever it takes to enter the resistor values. In my experience RPN always does the job with fewer keystrokes.