
Deconstructing Kitty - mkj
https://wp.josh.com/2018/05/07/deconstructing-kitty/
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mannykannot
This is a great example of how much information there is in the design of even
simple things, the way in which one design decision constrains others (why not
an iron core? Because the magnet would tend to stick to it. But why a magnet?
So we can push it. But why push it? Because it is easier to tell when the bob
has just passed bottom then when it is about to get there) synergy (with a
magnet, we can use the induced voltage in the coil to measure the movement)
and KISS (a simple knife-edge bearing.)

Another reminder to make my code as simple as possible.

~~~
madeofpalk
This reminds me of rice cookers, which seem to work like magic yet are
actually crazy simple devices - just a simple thermocouple that shuts the pot
off when the temperature reaches above boiling point (meaning there's no more
water left to be absorbed/turned into steam).

It's the sort of thing that means that even super cheap rice cookers from the
supermarket work great - that's all I've ever used.

~~~
JasonFruit
Why do they have separate settings for white and brown rice?

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seszett
I don't know any cooker with a brown rice setting, but this setting should
probably first turn the heat on, then turn it down and let the rice sit below
boiling point for a while, then turn the heat back on (though not as much as
with white rice).

It could still wait for the heat to suddenly rise in order to know when to
stop.

~~~
marak830
For standard long grain white rice, 1 part rice to 1.2 parts water. (Rinse
rice until mostly clear water comes out), put on the heat(no lid/cover) until
it just starts simmering(and I actually mean the preboil simmering). Heat to
extremely low and lid/cover on. Timer for 10 minutes. After the timer goes
off, heat off and timer for 12 minutes. Don't open the lid/cover at any stage.

That's how your rice cooker makes absorption style rice, and how you do it in
a pot. (Also a ton better than boiled)

Source: 18 year experience chef ;-)

~~~
JasonFruit
What about shaking the pot from time to time to keep the rice from adhering?
I've read that frequently but not seem it do anything in practice.

~~~
marak830
Don't need to, if you follow what I said, it will come out perfectly fluffy.

Also note I have made a mixture of multiple types of rice, same way, with no
issue.

Honestly I only actually learnt the Asian method about 5 years ago and was
kicking myself for not researching it earlier. It's so much better and
insanely reliable across different types of rice.

Edit: after it is done I tend to take the lid off, stir it and let sit for a
bit to let it air out. That helps a lot.

~~~
wrycoder
My method is similar, except that once it boils, I stir the rice once and then
simmer on medium high heat until the water level gets down to the surface of
the rice and steam pockets (“rice eyes”) appear. Then reduce heat to lowest
and cover for 20 min.

I’m going to try your fluffing method.

~~~
marak830
Do, I'll give yours a go as well. Always looking to learn new methods!

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DeanWormer
For those that don't know, this is Josh Levine's blog. He started Island ECN
and is prominently featured in Scott Patterson's Dark Pools
[https://www.amazon.com/Dark-Pools-Machine-Traders-
Rigging/dp...](https://www.amazon.com/Dark-Pools-Machine-Traders-
Rigging/dp/0307887189).

You can see the old homepage here
[http://josh.com/oldindex.htm](http://josh.com/oldindex.htm)

Some of his code (through acquisitions) lives on at the Nasdaq exchange. He's
a fascinating person in the history of electronic markets.

~~~
RubberShoes
One of my favorite books. Highly recommend

~~~
westoncb
Anyone one else want to weigh in on that? Sounds intriguing, but Amazon
reviews suggest it's ruined by technical inaccuracy.

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markatkinson
These cats are called Maneki-neko [https://en.wikipedia.org/wiki/Maneki-
neko](https://en.wikipedia.org/wiki/Maneki-neko)

~~~
majewsky
They're also in the logo of [https://media.ccc.de](https://media.ccc.de) \- At
CCC events, the podiums always have a maneki-neko, whose constant movement is
used by the video technicians to verify that the feed has not frozen.

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ehonda
Fun fact: Back in the early 00's, josh.com simply had a message saying
"josh.com is better than chris.com"

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howard941
Nice and elegant. Boss is a hardware dude with a compatible rule of thumb:
Don't use a micro until it has to do more than three things.

~~~
wrycoder
Unless the three things cost more than the micro :-/

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JasonFruit
This was a beautifully clear explanation — almost art. Often in question-and-
answer teaching the questions devolve into topic headings, but here he
anticipated and answered the questions I had and should have had. Excellent
and fascinating article.

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abetusk
An interesting tidbit talking about the coil used to push the magnet at the
end of the bob (the internal mechanism of the kitty hand):

    
    
        Why does the coil use air core rather than something
        like iron that would concentrate the magnetic field?
    
        Because then the magnet would want to stick to it.
    

Is there a nonmagnetic material that could be used to concentrate the magnetic
field? Aluminum?

~~~
lmm
I'm only going by what I just read on
[https://en.wikipedia.org/wiki/Magnetic_core](https://en.wikipedia.org/wiki/Magnetic_core)
, but it seems like a core only works by being magnetic itself. Note that "air
core" is a term of art; if there's a nonmagnetic (e.g. plastic or ceramic)
core it's still called "air core".

~~~
blattimwind
Copper being diamagnetic has a very low magnetic permeability, basically the
same as air, but now you have an eddy current brake.

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KaiserPro
These are sometimes called pulse motors, ez-spin or bedinimotors

[https://hackaday.com/2016/01/01/ez-spin-motor-spins-
forever/](https://hackaday.com/2016/01/01/ez-spin-motor-spins-forever/)
[http://bedinimotors.blogspot.co.uk/](http://bedinimotors.blogspot.co.uk/)

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uxp100
I thought the section heading "Why is the coil the secret sauce?" seemed very
dubious (as is acknowledged), but it's been long enough since I've done
electronics that I can't contradict it in any way.

But an analysis that focuses on the very low resistance of the wire and
ignores the back EMF from moving the pendulum seems wrong.

