Ask HN: Teach me something new • Hacker News Board

Re: Ask HN: Teach me something new

#461

Post by stavros » Sat, Apr 30, 2022, 1:17 PM UTC

atoav wrote: post #232

Ordering a typical printed circuit board with components placed on it is so cheap nowadays that this is a viable option for electeonic hobbyists nowadays (e.g. just ordered 50 pieces of audio output amplifiers at 3,49 € per piece (customs and shipping included), where 1.60 € would be the parts cost of the two chips on it. Only thing you need for this is: 1. An idea and some knowledge about electronics 2. An EDA softw…

This is 100% accurate and I recommend it. I know that most people reading this right now will say "this is so hard I don't even know where to begin", but, as with anything, once you know how it's done, it's trivial.

The parent comment is a good introduction, watch some KiCAD videos on designing circuits, the process is pretty foolproof if you design the schematic correctly, and then you basically "export Gerbers", upload them to the fab (JLCPCB), and you have PCBs in a few days.

Here's a small PCB I designed, together with Kibot project files that will error-check and export the Gerbers automatically:

https://gitlab.com/stavros/manual-fc

Install https://github.com/INTI-CMNB/kibot, run `kibot` in the directory of the designs, and you'll get files that are ready to upload to JLCPCB. Edit the designs etc to make your own thing, that should help you get started.

Re: Ask HN: Teach me something new

#462

Post by picklesman » Sat, Apr 30, 2022, 1:18 PM UTC

MaanuAir wrote: post #317

Adrig wrote: post #260

You probably heard about the quirks in the French numerical system. For example, 99 is translated "quatre-vingt-dix-neuf" which is literally "four twenty ten nine". This is a legacy of the base 20 numerical system used by the Celtics thousands of years ago before the modern Romance language drove it out. The hybridization with our current base 10 system came with the Roman conquest of the Gaul. Another example of the…

Thanks for this! As a French, I always wondered why this oddity. That should also be introduced when teachers explain hexadecimal :-)

Me too!

Btw, in the spirit of the title of this thread, in English you would say "as a French person". In the past, "Frenchman" was used but it's understandably out of favour these days.

"French" can be used as an adjective but not a noun in this context. It's a very common error, I suppose since "français" can be used as an adjective or a noun en français :)

Re: Ask HN: Teach me something new

#463

Post by rzzzt » Sat, Apr 30, 2022, 1:20 PM UTC

jiscariot wrote: post #387

f0e4c2f7 wrote: post #11

The command 'w' on a Linux box shows uptime, load, and who's logged in.

Nice. Those are the first two commands I usually issue after jumping on a box to investigate something.

Are "who" and "last" anywhere on the list?

Re: Ask HN: Teach me something new

#464

Post by thematrixturtle » Sat, Apr 30, 2022, 1:20 PM UTC

mikelevins wrote: post #28

I've described this on HN before; forgive me if you've already seen it. I have chronic migraine. It sounds worse than it is; I rarely suffer attacks anymore, and when I do, they're usually mostly harmless, as in the case I'll describe below. Contrary to popular belief, migraine is not a headache. It's something a little more like an epileptic seizure. Intense headaches are one common symptom, but there are a lot of o…

A simple demonstration of how complex our eyesight is: put your hand between your eyes, touching your nose, and compare what you see with the left eye closed and the right eye closed. On one side, knuckles, on the other, the palm. Yet when you open your eyes, your brain seamlessly fuses the images together and makes your hand largely disappear.

Re: Ask HN: Teach me something new

#465

Post by dinkleberg » Sat, Apr 30, 2022, 1:25 PM UTC

DeathArrow wrote: post #451

If you extend your arms sideways, the distance between the fingertips is equal to your height.

That is only truly accurate if you have an ape index of 1. But for most people it’ll be pretty close.

Re: Ask HN: Teach me something new

#466

Post by telesilla » Sat, Apr 30, 2022, 1:28 PM UTC

caseyslaught wrote: post #300

idrios wrote: post #119

In drug development, a lot of the engineering goes into making sure the pharmaceutical compound -- having been developed -- actually reaches the target area of the body. If the compound is a relatively large particle that needs to get into the blood stream, a nasal spray might result in the compound being deposited at the bottom of a person's lungs without ever getting absorbed. If stomach acids break the chemical do…

Grapefruit juice can also increase the amount of a drug absorbed into the bloodstream. It blocks an enzyme in the small intestine that breaks down many types of drugs.

We're told as young women to avoid grapefruit, it causes the anti-contraceptive pill to fail. Interesting, right?

Re: Ask HN: Teach me something new

#467

Post by elondaits » Sat, Apr 30, 2022, 1:29 PM UTC

scrollaway wrote: post #316

Take a few minutes to learn the NATO phonetic alphabet Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu Gotta spell anything over a voice line? Use it. No more screwing around with "B.. like Bryan, and then U, like .... under". s-c-r-o-l-l-a-w-a-y: sierra charlie romeo oscar lim…

Whenever I need to call an airline about a flight, I look up the NATO spelling of the reservation code. So far call center employees always understood me, used it back, and it made the communication extremely fluid.

Re: Ask HN: Teach me something new

#468

Post by ahnberg » Sat, Apr 30, 2022, 1:30 PM UTC

pards wrote: post #449

hiisukun wrote: post #123

In a lot of terminals, Alt+. (or Option+. on Mac) will paste in the last argument of the previous command. $ mkdir hi $ cd You can hit . several times to cycle through earlier final args.

Or ^r to search through the command history (bash only?): $ grep blah * $ ^r (reverse-i-search)`g': grep blah * This is far and above my most commonly used shell command

Then you can even superpowerboost the ^r by installing fzf! https://github.com/junegunn/fzf

Re: Ask HN: Teach me something new

#469

Post by thematrixturtle » Sat, Apr 30, 2022, 1:32 PM UTC

scrollaway wrote: post #316

Take a few minutes to learn the NATO phonetic alphabet Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu Gotta spell anything over a voice line? Use it. No more screwing around with "B.. like Bryan, and then U, like .... under". s-c-r-o-l-l-a-w-a-y: sierra charlie romeo oscar lim…

When calling an airline, ask if you can give them the PNR (Passenger Name Record, what your ticket calls the "booking reference") and then read it off with the NATO alphabet. You will get instant credibility with the agent on the other side as a flyer who knows their shit, plus it's hella fast.

Re: Ask HN: Teach me something new

#470

Post by leephillips » Sat, Apr 30, 2022, 1:32 PM UTC

Forgeties79 wrote: post #427

ajb wrote: post #229

In statistics, the mean and median are both averages, but are technically quite different. The mean is the sum of all items divided by the number of them, while the median is the middle item in the sorted list. When they are different, this can have strange effects. For example, when estimating engineering tasks, the mean error is often positive while the median is often negative. This is why your manager believes th…

Interesting. I always learned mean/median/mode were different things. The mean is the average, the median is the middle value, and the mode is the largest value. I wasn’t aware of this issue with conflating mean/median. That being said, I remember learning that and always wondering why I needed to know what “mode” was haha

The mode is the most common value, if it exists.