Concise electronics for geeks

[futmacl]

Hi folks,

I am always frustrated by how many reasonably accessible guides to electronics are very inaccurate, incomplete, or overly simplified; for example, the extremely popular hydraulic analogy may initially seem very useful, but in the end, is a misleading handicap when trying to understand the actual behavior of semiconductors, inductors, and so forth.

Because of this, I decided to put together my own primer, "Concise electronics for geeks":

http://lcamtuf.coredump.cx/electronics/

It is not perfect, but hopefully is accurate and useful enough to help many aspiring robot builders. Your feedback is of course very appreciated :-)

[voyager2]

Nice, i learnt more just skimming over it than i have in all the electronics books I've read thoroughly!
Amazing, still it takes a while to load, maybe divide it into multiple pages?

[Soeren]

Hi,

It is not perfect, but hopefully is accurate [...]

Only scanned it very briefly, but you attribute Watts law to Joule - and now James is crying (if not steaming) 

[futmacl]

Only scanned it very briefly, but you attribute Watts law to Joule - and now James is crying (if not steaming) 

Many sources do attribute this to Joule:

http://people.uncw.edu/olszewski/labsummer2/laboratory/joule.pdf
http://www.sci.sdsu.edu/classes/physics/phys196/ferguson/P196-28.Circuits.011.html
http://en.wikipedia.org/wiki/Electric_power

...but others indeed mention Watt:

https://ccrma.stanford.edu/wiki/Introduction_to_Electronics

[VegaObscura]

Under Ohm's Law:

This law is what makes resistors such useful components: they can be used to limit the current flowing through parts of the circuit to a specific, desired value; or, by creating voltage differences across resistor terminals, to create lower voltages for a variety of purposes.

This is something I've never been able to fully understand.  Will someone please explain to me, as if I were 5 years old, how a resistor reduces voltage?

[futmacl]

This is something I've never been able to fully understand.  Will someone please explain to me, as if I were 5 years old, how a resistor reduces voltage?

A single resistor connected to a perfect voltage source does not reduce voltage. The voltage across its terminals is equal to that of the voltage source.

Two resistors in series do: the voltage across these two resistors is equal to that of the voltage source, but the voltage in the middle is proportional to the ratio of resistances.

[VegaObscura]

This is something I've never been able to fully understand.  Will someone please explain to me, as if I were 5 years old, how a resistor reduces voltage?

A single resistor connected to a perfect voltage source does not reduce voltage. The voltage across its terminals is equal to that of the voltage source.

Two resistors in series do: the voltage across these two resistors is equal to that of the voltage source, but the voltage in the middle is proportional to the ratio of resistances.

Thank you.  I've been searching for that answer for over a year.  I don't get why all the information out there about resistors and Ohm's law discuss only the current drop and how to determine how much current you can reduce by applying a certain resistance, and never mention how the voltage drop works.

[Soeren]

Hi,

Many sources do attribute this to Joule:

http://people.uncw.edu/olszewski/labsummer2/laboratory/joule.pdf
http://www.sci.sdsu.edu/classes/physics/phys196/ferguson/P196-28.Circuits.011.html
http://en.wikipedia.org/wiki/Electric_power

...but others indeed mention Watt:

https://ccrma.stanford.edu/wiki/Introduction_to_Electronics

The ratio is a bit different:
joules law p=v*i
http://www.google.com/search?num=100&hl=en&safe=off&client=firefox-a&hs=lnd&rls=org.mozilla%3Aen-US%3Aofficial&q=joules+law+p%3Dv*i&btnG=Search&aq=f&aqi=m1&aql=&oq=&gs_rfai=
About 372,000 results (0.25 seconds)

watts law p=v*i
http://www.google.com/search?num=100&hl=en&safe=off&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=watts+law+p%3Dv*i&aq=f&aqi=&aql=&oq=&gs_rfai=
About 507,000 results (0.22 seconds)


Please read the following quotes from: http://en.wikipedia.org/wiki/Joule%27s_laws. They might help explain how it is and perhaps offer an explanation as to why some people attribute Watt Law to Joule:

Joule's laws are a pair of laws concerning the heat produced by a current and the energy dependence of an ideal gas to that of pressure, volume, and temperature, respectively.

Joule's first law, also known as the Joule effect, is a physical law expressing the relationship between the heat generated by the current flowing through a conductor. It is named for James Prescott Joule who studied the phenomenon in the 1840s. It is expressed as:

    Q = I^2 x R x t

where Q is the heat generated by a constant current I flowing through a conductor of electrical resistance R, for a time t. When current, resistance and time are expressed in amperes, ohms, and seconds respectively, the unit of Q is the joule. Joule's first law is sometimes called the Joule–Lenz law since it was later independently discovered by Heinrich Lenz. The heating effect of conductors carrying currents is known as Joule heating.

Joule's second law states that the internal energy of an ideal gas is independent of its volume and pressure, depending only on its temperature.

No sign of a direct mention of what is known as Watts Law.

And it continues:

In the context of resistive circuits and in light of conservation of energy and electrical potential, Joule's first law and Ohm's law are equivalent and derivable from each other (as explained by James Clerk Maxwell in 1881,[1] by Mascart in 1883,[2] and by Oliver Heaviside in 1894[3]), though they were discovered independently and experimentally, before the notions of conservation of energy and electrical potential were well developed.

Joule's first law states that the rate of heat dissipation in a resistive conductor is proportional to the square of the current through it and to its resistance. That is, the power dissipated in a resistor, in terms of the current through it and its resistance, is:[4]

    P = I^2 x R

Joule arrived at this result experimentally in 1841, using a calorimeter to measure heat, and a galvanometer to measure current, with a variety of resistive circuits.[5][6]

The law applies to any circuit that obeys Ohm's law, that is, that conducts a current proportional to the voltage across it, or equivalently, that can be characterized by a resistance. Ohm's law states that for a voltage V across a circuit of resistance R the current will be:[7][8]

    I = V/R

By substituting this formula for current into one or both factors of current in Joule's law, the power dissipated can be written in the equivalent forms:

    P = V x I = V^2/R

The relation P = V x I is actually more generally applicable than either Joule's law or Ohm's law, as it represents the instantaneous power being applied to circuit with voltage V across it and current I into it, whether the circuit is resistive or not.[1][9] In combination with either Ohm's law or Joule's law, it may be used to derive the other.[10]