Also, pretty much any image on the blog can be clicked on for a larger view if it is hard to read or see.
Units:
| V | Voltage | volts, EMF |
| A | Amps | electrical current |
| Ω, R | Ohms | resistance |
| W | Watts | power |
| Hz | Hertz | frequency |
| S | Seconds | um.. time |
| b | Bits | a zero or a one |
| B | Bytes | a grouping of 8 bits |
| F | Farads | capacitance |
| H | Henries (Henry) | inductance |
SI Prefixes:
Just put these in front of any type of unit to scale it
Just put these in front of any type of unit to scale it
| f | femto | 10-15 | 10fA = 10 femptoamps, very tiny |
| p | pico | 10-12 | 4.7pF = 4.7 picofarads, still small but realistic |
| n | nano | 10-9 | 5nV = 5 nanovolts = 0.000000005 Volts |
| u | micro | 10-6 | 3.3uS = 3.3 microseconds = 0.0000033 seconds, not long, but longer than you think |
| m | milli | 10-3 | 100mW = 100 milliwatts = 0.100 Watts |
| K | kilo | 103 | 12kΩ = 12 kilohms? = 12,000 Ohms |
| M, Meg | mega | 106 | 12MHz = 12 megahertz |
| G | giga | 109 | 4GB = 4 gigabytes |
| T | tera | 1012 | a large number, unless we're talking frequency or data storage, your whatever it is is probably on fire |
Equations:
Ohm's Law (rewritten so solve for each variable):
V = voltage
I = current
R = resistance
Power:
P = power in watts
V = voltage
I = current in amps
R = resistance in ohms
Decibels:
$dB_{volts}=20*log(\frac{V_{interest}}{V_{reference}})$, $dB_{power}=10*log(\frac{P_{interest}}{P_{reference}})$
I will hopefully explain dB's better at some point, but here's a short explanation. Decibels represent a difference between how large two things are, but based on powers of 10. For example, in audio, the rule of thumb is that an increase in 10dB equates to being twice as loud. So 80dB is twice as loud 70dB, which is twice as loud 60dB. However, in terms of power, 1000W is twice as loud as 100W, which is twice as loud as 10W. If a speaker SPL is rated at 100dB @ 1W, and you listen to background music at around 60dB, you need to bring the power down by 40dB. This is like halving the volume four times, and dividing the power by 10 each time you halve it. We get -40dB = $\frac{1}{10000}$ of our starting power, or 100uW. Yup, micro watts. And if you want to listen at rock concert levels, of say 120dB, you need to push 100W into the speaker. The problem is that the orders of magnitude vary so greatly for what seem like linear concepts of louder and softer. Thus we use decibels.
What are the reference voltages or powers shown in the equations? Well that depends. dB's are relative, unless you define a standard. If you are designing an amplifier that has a gain of 2, you can just calculate using a test case of an input with a magnitude of 1V (which would output a signal of 2V) , giving: $dB_{GAIN} = 20*log(\frac{2}{1})\approx6dB$. So regardless of what the signal was to start, the amplifier will increase it by 6dB.
But sometimes you really do need a reference, and there's a bunch of standard ones. Whenever you see a suffix, such as dBV, that's a signal relative to a reference. Both dBV and dBW are convenient as they both relate to 1V and 1W respectively. dBu on the other hand represents a voltage relative to that .775V. This goes back to a 600$\Omega$ standard load used in telephone and audio, and is the voltage required to produce 1mW across that load. I don't want to go further here, as there are a variety of dB types for radio, light, sound, etc.
A handy feature about dB's is that they do relate to each other. A 6dB gain in voltage will also be a 6dB gain in power. If you are measuring the same signal in dBV and dBu, if one reading jumps 10dB, the other one will too. The displayed values may be different, but their changes will be the same. The differences in value will always be a constant, it's sorta like Celsius and Kelvin.
That's enough on dB's as this isn't really the place for in depth explanation.
