Group project, to create a file of equations, rules of thumb and handy approximations

Harry Dellamano · 2006-05-11T02:08:20+00:00

This is a stolen idea, as most of mine are, from John Larkin in a previous thread, I will start it off with an equation for men's shoe sizes in the US. S = 3*L -22 S=shoe size L = length of foot in inches. So Shack (US basketball player) wares a size 22 shoe. His foot length is L=(S+22)/3= 14.7 inches, not so big. I ware a #14 shoe and my foot is 12" long. I am 75" tall. He should be 75*14.7/12 = 92"/12 = 7ft+6" which is correct. Ok, it is interesting but not electronics. We all must have helpful equations or rules of thumb that could be shared in this NG for the benefit of all. Cheers, Harry

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Phil Hobbs 20 years ago

355/113 is about 300 times closer. The connection between the Beast, Manhattan, and circles is amusing, though, thanks. That'll go into my "More reasons why numerology is stupid" file.

Other useful rules of thumb:

Signals in repeatered wires go at an average speed of c/10.

In a photodiode circuit at 300K, shot noise dominates when the photocurrent drops at least 50 mV across the load resistor (2 kT/e).

The noise temperature of a PN junction used as a load resistor is half the ambient temperature (150K at room temperature).

A BJT current source with an emitter resistor dropping V_d volts will contribute 25 mV/V_d times full shot noise current.

A BJT differential pair driven by a current source with full shot noise will exhibit exactly full shot noise in each collector, regardless of deltaV_BE.

Cheers,

Phil Hobbs

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Jim Thompson 20 years ago

Mine is easier to implement in a digital application ;-)

...Jim Thompson

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Harry Dellamano 20 years ago

Hey Wes, Good points, I will try to incorporate them in my future offerings. Harry

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Iwo Mergler 20 years ago

One nanocentury is about PI seconds.

Iwo

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Rich Grise 20 years ago

Megamall: 1E+6 shopping centers.

;-)

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martin griffith 20 years ago

Prefer megamaul

martin

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Ken Smith 20 years ago

In article , Jim Thompson wrote: [.. go read it ..]

This digital stuff is just a passing fad.

-- kensmith@rahul.net forging knowledge

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YD 20 years ago

The duration of the test being one ouchosecond.

- YD.

Remove HAT if replying by mail.

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Jim Thompson 20 years ago

Digital is just a subset of ANALOG ;-)

...Jim Thompson

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

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Carl Smith 20 years ago

Is anything really analog when the electroncs have a quantized charge? :-)

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Ken Smith 20 years ago

I always try to control the positions of the electrons and not their charges. Even though controlling the positions of electrons can be a little like herding cats, it is still easier than trying to modulate their charge.

-- kensmith@rahul.net forging knowledge

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Jim Thompson 20 years ago

I regularly redesign logic/digital circuits without any problem whatsoever.

Show me a digital designer who can do the same with an analog circuit.

...Jim Thompson

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

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Rich, but drunk 20 years ago

And Tarzan can grab you a snack in a banasecond. ;-)

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Rich the Philosophizer 20 years ago

Aren't position and velocity, like, 90 degrees out of phase?

Thanks, Rich

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Sandbox Moderator 20 years ago

Try not to dislocate your shoulder there, Jim.

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Michael A. Terrell 20 years ago

Not since Cheetah greased one of his vines. :( BTW, those Tarzan movies were shot a few miles from here at Silver Springs, Florida, and some of the monkeys escaped and ran wild for years around Ocala.

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Harry Dellamano 20 years ago

Ok, how about capacity in a PCB of FR-4 material. Two mirrored surfaces, each of area A, separated by T, all in inches and Farads. C=(A*10^-12)/T or 1nF/sq"/0.001" Cheers, Harry

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