How pencil tire pressure gauges work | Hacker News Reader

How pencil tire pressure gauges work

blog.oppedahl.com

54 pointsbumbledraven12 comments

This is interesting. I read this link because I've been curious about exactly how these work, and I like knowing that sort of thing.

Turns out, it works precisely how I would have expected it would work, and indeed, probably using the first approach I would have used for designing such a thing (granted, I'm not a mechanical engineer.)

Most things I learn about do NOT fit expectations that well. Truly a simple, practical device.

Also, incidentally, all the pencil gauges I have are +/- 5 psi relative to my digital gauge, so despite all these balances it might only be an approximate technique after all.

I had "Unusual sources of energy" class at University. One day we were sitting in the classroom, the teacher was there but the class didn't started yet. I was eating one of those extruded styrofoam cracker and I noticed on the packaging there was a nutrient information, I converted it 1:1 to electric energy and calculated that one cracker could power single LED diode for 6 months. It seemed wrong so I told it to the teacher and asked him how they actually calculate the energy of various foods and when he said they burn it, I bursted into laughter because I honestly imagined some more sophisticated method.

I believe they no longer use the burning method [1] for measuring food energy, since it overestimates energy of high-fiber foods (fiber doesn't get burned when in the body, but it does get burned during measurement.) I believe nowadays they estimate the caloric content based on the fat, carbohydrate, and protein content of the food.

[1] https://en.m.wikipedia.org/wiki/Calorimeter

A good youtube video on the subject of the energy content of food and how efficient the body is at using it.

https://www.youtube.com/watch?v=9wZ0wTqJIxY

To me, the fact that these things are omnipresent for 99 cents is just as much proof that our species can do pretty much anything, as much as it is that we have levitating trains.

These things are very cheap to produce, don't have a lot of parts, are small and light (cheap to transport).

A few days ago I bought a 12V air compressor (for filing car tires) for 6.99€ (it was a reduced price, but at a store where everything is always reduced... the base price was 9.99€)

So... 22% VAT removed, then the sellers margin, shipping a not-that-small box from china... then you add the shell packaging, papers inside, the electronics, the motor, the pump part, pressure gauge, plastic shell... then you have to account for all the fauly ones..

I honestly have no idea how they can make something that cheap.

Having had recent, in-depth personal experience with these things, PART of the answer is that they're crap. They almost don't exist, in that a working one is rare. Each one is really just a probability of functionality; a non-functional replica of some ideal product. They will almost certainly break with relatively low amount of standard usage (or the usage they support is ridiculously unrealistic, like not using them in temperatures over 86 F). And this is because their pipelines are optimized to produce the parts as cheaply as possible; just enough to physically exist and work, perhaps, a few times. They will be sold under different names over time so people won't be able to share their experiences. And of course, they are made in places where human suffering and pollution are not penalized.

Hello folks. I am the person who wrote that blog article. I will be delighted if people might actually post their comments on the article itself! I am fascinated that someone thought I was writing like "a children's book". I am also fascinated that someone said "It's very very weird. Also seems like they are making it all up based on their assumption of how the internals could fail. Kind of feels like SEO content to me." I can promise you that when I write this blog, I never give even a moment's thought to SEO things. My guess is that most readers of this "Hacker News" site would find other articles of mine to be interesting: https://blog.oppedahl.com/?cat=13 .

Always wondered how these actually work.

What's up with the writing? Its written like a children's book, I had to pause reading to scan around a few times feeling a bit self conscious that I was on a kids explainer website.

It's very very weird. Also seems like they are making it all up based on their assumption of how the internals could fail. Kind of feels like SEO content to me.

Hopefully it's not AI generated

I don't think I've ever seen one up close, so I assumed it had to do with how fast the air rushes out, in a way overcomplicated way.

I thought maybe the design was such that the farther away it was, the less it would get blown on, and a given pressure would be able to make a certain amount of inertia before it was too far.

For some reason I imagined people had to manually push it back in and reset it, so there couldn't possibly be a spring.

I didn't even know they had springs at all! I'm sure I would have figured it out if I had examined one though, since it's basically a piston on a scale.

Reply on news.ycombinator.com