UmbralRaptor changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> … one of the other grad students just compared me to nomal O_o | <ferram4> I shall beat my problems to death with an engineer.
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<soundnfury>
> study benzene
<soundnfury>
> postulate a ring structure
<soundnfury>
top kekule
<UmbralRaptor>
?
<soundnfury>
Dreadful pun, nothing more
<soundnfury>
"Have you ever heard of campanology?" "I think so; it rings a bell."
<SnoopJeDi>
HAH
<Ellied>
peh. My kingdom for a gigaohm resistor
<Ellied>
(we have nothing larger than 10M and all my photodiode amplifiers have terrible gain)
<Ellied>
I tried adding a second stage, but that just made it go utterly nuts
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* Ellied
stabs DC offsets
<Ellied>
;mission
<kmath>
Ellied: You attempt to explain specific impulse to third-graders. You discover that Eve's oceans are puddles of gray goo in the most unpleasant way possible.
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<whitequark>
;mission
<kmath>
whitequark: You start an Action War. Do you really need that many boosters?
<egg|zzz|egg>
!wpn whitequark
* Qboid
gives whitequark a split tube
<whitequark>
!wpn egg|zzz|egg
* Qboid
gives egg|zzz|egg a critical lobster
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<Iskierka>
Ellied, make your own Gohm resistor with crocodile clips and a pencil lead?
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<whitequark>
Iskierka: Gohm?
<whitequark>
with a pencil lead?
<whitequark>
resistance of a pencil lead is in like hundred ohm to ten kiloohm range
<whitequark>
try it
<whitequark>
a Gohm resistor would be more like... using the pencil itself
<Iskierka>
Figured they're not supposed to conduct well, never tried it
<whitequark>
it's carbon.
<Iskierka>
use super-thin mechanical pencil leads?
<whitequark>
why on earth would it *not* conduct well
<whitequark>
those conduct exceptionally well, perhaps because they contain less binder
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<whitequark>
try putting a mechanical pencil lead, maybe 0.5mm, on the leads of a 12V battery
<Iskierka>
I was thinking of that and figured it's the high resistance that makes it explode but I now recall that's the opposite of the relationship. Not done direct electrics in a while
<Iskierka>
so fair enough
<Iskierka>
instead find something else like paper to make into a Gohm?
<whitequark>
just buy a gohm resistor?
<whitequark>
I think commercial ones go up to like 10Gohm
<whitequark>
problem is you usually don't have any good way to measure how resistive it is
<Iskierka>
you'd've thought an electronics lab would have them then but google can answer
<whitequark>
if you don't already have any
<whitequark>
they're rare and usually not present in resistor sets
<whitequark>
because most people never need any
<whitequark>
but they are definitely sold commercially, for one, HV resistors need that
<Iskierka>
most people, but an electronics lab that apparently does have things that GG needs them for, you'd've expected a couple lying around
<Iskierka>
I was just trying to think of something that wouldn't need delivery time though.
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<egg|phone|egg>
!Wpn UmbralRaptor
* Qboid
gives UmbralRaptor a visible Ꙭ
<egg|phone|egg>
!Wpn Iskierka
* Qboid
gives Iskierka an isentropic delta function
<egg|phone|egg>
!Wpn whitequark
* Qboid
gives whitequark a bismuth espresso
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<Ellied>
Iskierka: we have a drawer for 1 GΩ resistors, but it's empty. Actually, when I came, it had a few unmarked 1W resistors in it that turned out to be like 10k
<whitequark>
lol
<whitequark>
1W 1GΩ resistors
<whitequark>
that's... 1 megavolt?
<SnoopJeDi>
RIP
<Ellied>
31 kV by my calculations. Isn't Vmax = sqrt(PR)?
<Ellied>
er, more like 32 kV, I suck at remembering to round
<Ellied>
P = IV & I = V/R → P = V²/R, so V² = PR
<SnoopJeDi>
At least that's no longer in "~meter long arc in air" voltage territory
<Ellied>
we have a surprising number of 1W 1MΩ ones though. that's a nice round 1000 volts.
<Ellied>
yeah lol, one has to wonder if 1W resistors in standard packages in the 10 GΩ range would even be useful, 1 kV might find a better path across ~2 cm of air than through the resistor.
<Ellied>
er, 100 kV
<SnoopJeDi>
1-100 kV isn't particularly exotic AFAIK, but I'm not an electronics
<whitequark>
Ellied: oh yes you're absolutely right
<whitequark>
I'm sick and it shows
<Ellied>
SnoopJeDi: I haven't had occasion to work with such voltages, so that was just a guess
<SnoopJeDi>
I only say that because of CRTs
<Ellied>
ah yes
<SnoopJeDi>
which is the closest thing I really have to actual exposure to them (I don't count magnets)
<whitequark>
1-100 kV aren't especially rare
<whitequark>
your microwave oven has osmething like 5 kV inside it
<SnoopJeDi>
ah yea magnetrons
<SnoopJeDi>
yea in the land of RF, kV is peanuts
<whitequark>
or power transmission lines
<SnoopJeDi>
the cavities I'm using in this simulation are O(10) MV/m
* SnoopJeDi
abuses big-oh notation
<Ellied>
yeah, that's why I'm so afraid of the thing. it looks like someone pulled it out of a trash dump (the guy renovating my apartment last summer told me the people who sold him my shitty stove threw it in for free)
<Ellied>
if it had a metal front panel, I would just refuse to use it
<Ellied>
but I can't afford to buy a new one in the meantime, so there it sits.
<SnoopJeDi>
I still don't really understand magnetrons, or RF in general
<Iskierka>
it's totally normal to power three computers off one PSU, right?
<SnoopJeDi>
something something waveguide
<SnoopJeDi>
although speaking of waves, that PCI signal reflection thing was a fun read whitequark
<Ellied>
RF is weird. in my work so far, it's mostly been an annoyance that I have to figure out how to get rid of every time I string a wire longer than $ANNOYINGLY_SHORT_DISTANCE.
<Ellied>
and also the magic handwave word to answer the question "why does this commercial circuit board look completely insane"
<SnoopJeDi>
Every time I sit through an RF talk at a collaboration meeting, it's like I'm attending a seminar hosted by Merlin
<SnoopJeDi>
an RF engineering talk, anyway
<SnoopJeDi>
I'm reasonably comfortable with RF dynamics in a "who cares where E came from it's just a force now" sense
<Ellied>
whitequark: oh, I just got a module in the mail that looks a lot like that. That wouldn't happen to be a short-range doppler radar motion detector, would it?
<whitequark>
an X-band doppler radar, precisely
<Ellied>
they didn't bother to solder the shield down (as is apparently the case in that picture too) so I pried it off, and underneath was all of... three parts!
<Ellied>
er, four.
<whitequark>
nine?
<whitequark>
I can even explain how it works
<Ellied>
a resistor, a capacitor, a little three-pin SOT-23 with two of the pins shorted together, and a little four-pin thingy. that's all mine has.
<Ellied>
also that plastic thing that sits underneath the screw on the shield.
<whitequark>
photo?
<Ellied>
I left it at school, I'll take one when I get there, unless I can find one by googling
<Ellied>
the red thing in the bottom right is about where the SOT-23 thing is in mine
<whitequark>
ohhh I see, wow they cheaped out even more
<whitequark>
the round white thing is a ceramic resonator
<Ellied>
it is? It's not even connected to anything at all
<whitequark>
the four-pin thing is a fully integrated RF oscillator. the resistor is current-limiting (mine has a zener, at least)
<whitequark>
yes, it is
<whitequark>
it's coupled through the dielectric
<whitequark>
anyway. the circle sector things are RF blocks
<Ellied>
wow
<whitequark>
tuned LC circuit, essentially
<whitequark>
depending on position it could either absorb or reflect RF (so an open or a short)
<SnoopJeDi>
anything special about the angle of π/4 between them?
<whitequark>
the cap is DC block
<whitequark>
don't think so
<whitequark>
and the thing with two terminals shorted is a diode half-bridge
<SnoopJeDi>
ooh, that picture is from a teardown
* SnoopJeDi
bookmarks
<whitequark>
it acts as a mixer
<Ellied>
What I can find on the web suggests that this device basically just puts out a very small (a few microvolts) signal at some frequency and the carrier device has to deal with amplifying and filtering the signal to figure out if there's anything moving.
<whitequark>
hm
<Ellied>
a mixer?
<whitequark>
weird
<whitequark>
mine outputs like a 0-5V signal
<whitequark>
you can just feed it directly into a micro
<whitequark>
a mixer.
<Ellied>
yeah, that's what I was hoping this one would do
<whitequark>
gives you a sum of several signals.
<whitequark>
in this case uhh
<whitequark>
it sums the input signal with two phase-shifted versions of the output signal (the two pins being shorted are not actually shorted, it adds a phase shift)
<Ellied>
oh, gotcha
<whitequark>
I'm not super certain what the math is but I'm sure egg can crack that in like three minutes
<Ellied>
heh
<SnoopJeDi>
the quantity you're interested in measuring with doppler is usually [signal]+[shifted signal], and you extract the beat ω
<SnoopJeDi>
although RF is slow enough that I guess it's not strictly a necessity?
<SnoopJeDi>
you don't really have an option once you get up into the optical though, so that's how laser gyros work
<whitequark>
so mine outputs nothing (the output stays at the exact same analog voltage) when you don't move
<Ellied>
the device has four external terminals, two GND, one +5V, and one "IF"
<whitequark>
yes, the output frequency of the mixer
<Ellied>
I see, so the beat frequency is going to appear there?
<whitequark>
ye
<Ellied>
so will the post-amplifier to pick up that signal need to be especially fast? I don't have a sense of how fast a signal I can expect.
<whitequark>
whats the frequency?
<whitequark>
actually, wait
<whitequark>
do we even need that?
<whitequark>
lemme think
<Ellied>
I should know how to calculate that...
<SnoopJeDi>
~ ω_A - ω_B
<SnoopJeDi>
can't recall if that's the one wot gets a factor of 2 or not
<whitequark>
right so E=hf, and you're changing the speed of the photon by the speed of your moving object
<whitequark>
thus blue- or red-shifting it
<Ellied>
I mean the amount of frequency shift for the speed of the moving thing
<SnoopJeDi>
the shift in the frequency due to the Doppler effect, or the frequency of the signal at the mixer output?
<whitequark>
aren't those basically the same?
<Ellied>
presumably the output frequency is 10 GHz beating at that minus the received frequency, right?
<Ellied>
or is there some magic that only produces the beat frequency?
<whitequark>
Ellied: you get two images
<whitequark>
one near 10GHz and one near 0Hz
<whitequark>
the former is easily filtered out
<Ellied>
I see, so you feed the IF pin output through a small low-pass filter and then you get the beat frequency.
<SnoopJeDi>
whitequark, I guess it depends what you call "the signal" at the output of the mixer, heh.
<Ellied>
then amplify that, rectify it, and you've got something you can feed to an MCU?
<SnoopJeDi>
what I was thinking was sloppy because I was trivially discarding the fast component in my head
<whitequark>
Ellied: it's likely already filterd at that PCB
<Ellied>
right, I saw the bit about that in the article.
<SnoopJeDi>
Ellied, the farther you go down the rabbit hole, the worse it gets :/
<SnoopJeDi>
although you'd probably get a kick out of multipacting
<Ellied>
"There are only four components!" "WRONG! that thing that doesn't even look connected is a component too, and there are like 17 INVISIBLE components!"
<Ellied>
multipacting?
<SnoopJeDi>
resonant emission inside of an RF structure --> lots of electrons --> owwie-times for the cavity surface (which is generally quite finicky)
<SnoopJeDi>
pretty specific to accelerators, granted
<SnoopJeDi>
and RF technology is a muuuuch bigger lake than just my little corner emcompasses
<SnoopJeDi>
ooh you'd probably also like stochastic cooling
<Ellied>
cool, it's just a factor of 2Δv/c?
<whitequark>
so for 10 GHz
<whitequark>
> (2*1cm/s)/c*10GHz -> Hz
<whitequark>
approx. 0.6671281 hertz (frequency)
<whitequark>
which is precisely what I've seen on my radar, of course
<Ellied>
wow, you can pick up motion that slow? I'm surprised
<whitequark>
arbitrarily slow.
<whitequark>
you can pick up mm/s.
<Ellied>
damn
<whitequark>
the problem is picking up motion far away and/or of a small object
<Ellied>
sure, that makes sense
<Ellied>
is it... it's not just the angular size of the object from the module's position that determines its detectability, is it?
<whitequark>
it should be conductive
<whitequark>
reasonably
<whitequark>
metal is great, humans are ok
<whitequark>
dunno about plastics but i think you're gonna have a harder time
<Ellied>
gotcha
* SnoopJeDi
mumbles something about the F-117
<whitequark>
shush
<SnoopJeDi>
Ellied, the inverse scattering problem is one of the unsung beauties of the 20th century
<SnoopJeDi>
and certainly not one we're done with
<SnoopJeDi>
Going to the library to get a monolith by Petr Beckmann on the subject ("The scattering of electromagnetic waves from rough surfaces", IIRC) was how I discovered his (far more interesting) "A History of Pi"
<SnoopJeDi>
err, monograph
* Ellied
imagines SnoopJeDi carrying home a monolith from the library
<SnoopJeDi>
the coppery (?) structure in the background is the AOK library, probably my favorite scene on UMBC's campus
<egg|zzz|egg>
whitequark: you rang?
<Qboid>
egg|zzz|egg: rsparkyc left a message for you in #principia [27.04.2017 17:18:26]: "i think i got a contract system for Legrange points worked out, working on putting together a build"
<SnoopJeDi>
!wpn egg|zzz|egg
* Qboid
gives egg|zzz|egg an impedance-matched mission
<SnoopJeDi>
well done Qboid that's very apropos
<bofh_>
whitequark: what are you doing with X-band doppler radar anyhow?
<egg|zzz|egg>
!wpn whitequark
* Qboid
gives whitequark a nasal buzzard
<egg|zzz|egg>
!wpn bofh_
* Qboid
gives bofh_ a modular metric
<egg|zzz|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a power boat
<whitequark>
bofh_: nothing, it was just really cheap and I never touched anything using a frequency that high before
<whitequark>
it was like... $8
<whitequark>
"wow, a real radar for this much!!"
<SnoopJeDi>
living in the future is a really neat experience
<SnoopJeDi>
uh if we sweep designer smart juicers under the rug a bit
<whitequark>
lol
<SnoopJeDi>
although Ellied RT'd someone who pointed out that Juicero is a pretty afforable 4000 lb press for hardware hack sorts
<UmbralRaptor>
Can we just use a custom built 4000 lb hydraulic press on them?
<whitequark>
uhmmmm no
<whitequark>
no
<whitequark>
absolutely fucking not
<whitequark>
a hydraulic bottle from your nearest hazard fraught is like $20
<kmath>
<mhoye> Lazyweb: How do we repurpose the Juicero hardware? It's a bullshit kitchen device, obvs, but a very cheap 4000lb press. How can we reuse it?
<SnoopJeDi>
but yea
<egg|zzz|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor an impedance-matched bombe
<UmbralRaptor>
!wpn egg|zzz|egg
* Qboid
gives egg|zzz|egg a table-like catstrophe
* egg|zzz|egg
pets UmbralRaptor with a cat
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<soundnfury>
what do you call a theatre organ that explodes if you look at it funny?
<soundnfury>
a hexanitrohexaazaisowurlitzer
* soundnfury
gets coat
<egg|zzz|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a zonal physicist which vaguely resembles a hexagon
<soundnfury>
!wpn egg|zzz|egg
* Qboid
gives egg|zzz|egg an ascending Coxeter egg|zzz|egg
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* UmbralRaptor
hands soundnfury his mass in octanitrocubane.
* soundnfury
drops it, while UmbralRaptor is still standing nearby
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<soundnfury>
I guess Technicalfool was standing nearby too
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<UmbralRaptor>
Confusingly, it's supposed to be decently stable.
<soundnfury>
UmbralRaptor: clearly it has insufficient nitrogens, then.
<soundnfury>
also, can it form a peroxate?
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