21Apr/1045
Circuit Diagram
by Jeff
Image text: I just caught myself idly trying to work out what that resistor mass would actually be, and realized I had self-nerd-sniped.
Alright, I'm going to have to own up to this one, all of these are jokes and puns on circuits and circuity designs. But, I have no idea what each one is referencing. Hit it up in the comments below and let me know what the individual phrases and designs mean.
Yes, I'm an idiot, I know. But, I need your help. Yes, you. Let me know what you know about circuits!
April 21st, 2010
I know I’m not getting all of them, either.
This is making fun of complicated circuit schematics, so some of the stuff in it is just general absurd complexity. Other stuff is more specific jokes.
The “arena” device is connected to three diodes, which allow current to flow in one direction only. In this case, two enter, but only one leaves the arena.
Down, and to the left, of the Arena is a mini circuit labeled “may use an actual sandal instead”. The mini-circuit is a text-book example of a “flip-flop”.
The various ends which look like three horizontal lines in a triangle (like what’s in the holy water) are ground connections — hence one labeled “bury deep, but not too deep”.
The 666 timer is a play on the venerable 555 timer.
The element labeled “3 liters” is a variant on a capacitor symbol, which normally has only two lines.
A standard problem in early electrical engineering classes is to figure out the equivalent resistance of some network of resistors, like in the “resistor mass” referred to in the image text. This has been used as a joke in an earlier XKCD I don’t have time to look up right now.
The Arduino is a popular platform for hobbyists to make electronic controllers for things. It’s open sourced, and has a large following on the blogosphere. No project is complete without an Arduino in it.
The 5Ohm decoy resister has no use; it connects to nothing.
Squirrels and bats often get into circuits, usually unplanned and with disasterous results.
Magic smoke is what makes ICs work. Once you let the magic smoke out, they no longer work.
The circle with a sine wave labeled “240V” is a 240V AC generator. The connection around it would be a short, and in a real circuit would immediately heat up, cause circuit breakers to trip, might start fires, might even explode from the current. Hence the taunt about being a wimp if you omit it.
The diamond configuration of diodes labeled “moral rectifier” is a bog-standard full-wave bridge rectifier circuit.
Organic chemistry molecular diagrams can resemble circuits (especially resisters), so it’s nice to acknowledge that this circuit has a methyl group right above the arena.
There’s a lot more, but I’m out of time.
April 25th, 2010
>The “arena” device is connected to three diodes, which allow current to flow >in one direction only. In this case, two enter, but only one leaves the arena.
This is probably obvious to most readers, but I’d like to underline that this is a reference to Mad Max. The rules of the Thunderdome, a fighting arena, are “Two men enter, one man leaves”.
July 9th, 2010
> Down, and to the left, of the Arena is a mini circuit
> labeled “may use an actual sandal instead”. The
> mini-circuit is a text-book example of a “flip-flop”.
That’s not a flip-flop, it’s a latch.
April 15th, 2011
It is a D type flip flop (which is a latch)
May 20th, 2011
…for people with wide feet.
October 13th, 2011
It certainly isn’t D type: there’s no inverter, or Enable input. It’s an SR latch.
April 21st, 2010
I think this was a test to see what Jeff would say about it.
If only he had included a little “Explain this” somewhere, I would be certain.
April 21st, 2010
Right above I-95 there’s a flux capacitor. The “touch tongue here” gap is probably just a joke about people testing 9V batteries that way. I think my favorite is “Not a resistor, wire just does this.”
April 21st, 2010
The voltage source at the top with the square root of 2 is a pun on an answer to electric circuit that is very common.
Under it the resistor with 120 ohm or to taste is a classic in analogue circuit, the value you come up to with math are not the value you have to put, you have to guess the real one.
A bit to the right the transistor has two input arrow, since the third wire does not output current there is no way out.
Next to it, the resistor with the brown blue orange is the value of the resistor. On the resistor there are colored lines that indicates the value and precision of the measurement. Here brown = 1 blue = 6 and orange = x1000, so 16kOhms. Since there is no gold or silver band at the end the error is about 20%.
Next to the most expensive chip, the electron single file is a reference to how we represent a current in a circuit. A line of electron traveling in a wire.
The electric eel is a twist ion electric field, but I’m not sure.
Near the holy water the resistor with the value of pi is again a joke on a regular value use and obtain in circuit calculation.
At the top left, the mixer is a reference on the signal mixer circuits. Next to the I-95 the y is a reference to the Y and Delta configuration three phase circuit.
The magic smoke seems to be a reference to the smoke coming out from the capacitor that explodes from being wrongly connected.
The tear collector, is a diode that trigger with the light (the reverse principle of the led).
April 21st, 2010
Actually, I think the first comment about magic smoke was more accurate. It’s not about anything exploding, it’s about explaining away how some ICs or passive elements work without getting into details. If you open one up, the magic smoke will leave and that element will never work again.
April 22nd, 2010
No, he is exactly right. The analogy is that once an IC component shorts and arcs, it emits the tell-tale smoke.
Because it arc’d, the IC component no longer works. Since the smoke is an indicator of a broken component, the joke was that the “magic smoke” left the building.
tl;dr he was right.
April 22nd, 2010
I think the Y is supposed to be a flux capacitor from the infamous Back to the Future, where I-95 would be a road on which Marty and the Doc used their DeLorean time machine to travel through time?
April 21st, 2010
The main theme to me appears to be playing with expectations. Circuit diagrams are pure topology and symbols, so all references to things with physical dimensions are unexpected, e.g. solder blob, pull this wire tight, hot glue. Some of the symbols also cross into other disciplines such as the CH3 molecule and a cloverleaf freeway intersection.
April 21st, 2010
“Self-nerd-sniping”… isn’t that a reference to sending yourself on a nerd quest to determine the undeterminable? (The proverbial Snipe hunt.)
April 21st, 2010
Self-nerd-sniping is a reference to the previous XKCD comic at http://xkcd.com/356/ where you try to get physicists and mathematicians run over by asking them to figure out the resistance on a complicated circuit while they’re crossing the road.
April 21st, 2010
Unless I’m mistaken, all the parts are references to movies.
April 21st, 2010
<<>>
Such as?
Since I discovered “Explain,” I assumed it was only a matter of time before XKCD did something just to drive Explain nuts.
April 21st, 2010
– references to movies. –
Such as?
Since I discovered “Explain,” I assumed it was only a matter of time before XKCD did something just to drive Explain nuts.
April 21st, 2010
I’m just making this worse, aren’t I? I can’t edit my own post.
Koz
April 21st, 2010
I wonder how many of these I can stack before somebody catches me?
Koz
April 21st, 2010
Wouldn’t it be nice to edit or delete an old post of your own?
Koz
April 22nd, 2010
The huge mass of resistors to the right is a nightmare of a problem. At first glance it appears to be a typical (but huge) Y/Delta configuration, but some of the wires are not actually connected, making all the calculations more of a nightmare, hence the taunt “Oh so you think you’re a whiz at EE201?”.
The moral rectifier is a play on rectifiers. This one boosts moral it seems.
The rest that I know has already been covered.
April 27th, 2010
I’m pretty sure that it’s a pun on “moral rectitude.” http://thesaurus.com/browse/moral+rectitude
April 23rd, 2010
“HIRE SOMEONE TO OPEN AND CLOSE SWITCH REAL FAST” probably refers to a clock generator. I think.
There also appears to be a short circuit across the 240V.
April 12th, 2011
It’s probably just a square-wave generator. Early radio controls used to do mark-pulse ratios in just this way, with a relay doing the open/close real fast…
April 23rd, 2010
The Smiling face and the ballon could be a reference to “Billy’s Ballon” by Don Hertzfeld. http://www.youtube.com/watch?v=TWY1eupbMbU
April 23rd, 2010
Consider me nerd-sniped. I got 0.78 Ohms (more accurately, 13299/17052 Ohms). I’ve actually been searching the net for an answer to compare it to. I haven’t done this stuff in over 10 years, so I was curious if I still could.
My personal favorite part is the arena, where I presume two electrons enter, they fight to the death, and the only the victor can leave (enforced by diodes).
April 25th, 2010
got somthing like .75
May 6th, 2010
Grrrrr, solved this 3 times, and got 3 different answers
The latest one is 1.335 (more accurately 91691 / 68665)
Sigh… 28 linear equations… It’s hard not to slip at one of the multitude of steps….
Oh well, on to the 4th time
May 6th, 2010
Damn, I think I’ve slipped at the end. That should have been a reverse –
68665 / 91691. So now my answer is ~0,7489 Ohm.
We are getting pretty close to consensus
May 8th, 2010
Oops…double checked my work and found a couple mistakes. I now get 75795/101349 = 0.74786135.
Here’s what I have for the current going through each resistor:
http://dwoods.org/files/xkcd_network_values.png
I tried tracing around various paths to check, and it’s looking pretty solid to me. Let me know if I missed one.
Cheers!
May 9th, 2010
Oops…should probably have specified this regarding my diagram…for “ease” of calculation, I assumed there’s 1amp going through the network. Then, I could figure out the resistance and remove my assumption.
May 10th, 2010
It’s OK, no confusion with that
. You also could have assumed the 101349 Amp current going through your network – this makes all the current values whole numbers. Also, not simplifying the fractions makes it easier to check the result (1425/11261 should be left as 12825/101349 for ease of checking).
May 10th, 2010
Dan,
.
I’ve checked your solution and it seems correct. Currents balance for all the vertices and EMFs balance for all the contours.
Hence we can declare your solution as THE SOLUTION
I’ve checked mine also and found that I’ve made a mistake during
. Hence my solution balances all the currents and all the emfs except for the emf of one contour (for reference – the one build of the 310+9641-3317*3 currents in your solution). Thats the cause of slight disagreement in our results.
the building of the equation system – simple hand slip – number went to the neighboring Excel cell
Sigh… I guess at this rate we can probably be nerd-sniped not only by the trucks but by the yearly cruise ships
.
On the other hand, I wonder how much points are electrical engineers (or programmers). If physicists are 2 and mathematicians are 3 points, I’d hope that the other folk rates at least 1pt.
May 15th, 2010
i think the electric eel is a play on the symbol for a fuse.
May 18th, 2010
The 666 timer is a reference to a 555 timer which is commonly used as a clock in circuits. The pin connecting to “?” makes me think the whole circuit is likely clocked by the devil.
The 11 kg inductor (under the batman symbol) references how some inductors (coils of wire) can be huge.
The “Neck Strap” probably references anti-static wrist straps.
The mess in the lower left makes me think of Boston, MA. I-95 is a highway near Boston, and if anyone has tried to drive in Boston they would encounter a road configuration similar to the wires (that is confusing, twisty roads).
The “holding pen” is a play on how a latch works to store data.
Anyways those are a few of my observations…
June 17th, 2010
First, the 666 timer is an obvious 555 reference. The unconnected pin just makes it clearer.
On a 555, the unconnected pin, Pin #5, is the Control pin, which connects to the inside of the second comparator. Typically, you don’t need it, and prevent noise from getting in and giving your circuit trouble, you connect it to the ground via a 10nF Capacitor. However, some circuits don’t connect it, and the pin #5 here seems to laugh at this.
July 14th, 2010
One point that seems to have been missed is the combination (at random) of AC and DC
July 14th, 2010
Also the EKG at the bottom next to the lamp
July 21st, 2010
I have confirmed the solution of 0.74786 Ohms as well. Once on a circuit simulator and once on Mathematica.
August 12th, 2010
we always use General Electric circuit breakers at home because it is very reliable;*:
October 16th, 2010
“Most Expensive Chip Available” is a reference to the Monty Python: Meaning of Life movie, in which a lady is in a hospital room about to give birth. The doctors, coming into the room, decide the room doesn’t have enough equipment and call for the assistants to bring in this long list of machines. Among them was the “Most Expensive Machine”.
Bottom right, next to the “Take of shirt while wearing…” is an Electric Inductor… I’m not really sure what the pun here is…
January 1st, 2011
Why doesn’t anyone see the obvious meaning here? Maybe a few things are actually references, like the 666 Timer, but most of it is just the absurdity! You would never find a batman symbol in a circuit, so to see it in circuit plans is absurd! These things were put in because they seemed to vaguely fit, or were jokes about circuit diagrams, but were so absurd that it would be funny! You’re trying to look too deeply into meanings that just flat out aren’t there!
November 6th, 2011
just cause no one has done it yet
Top left is a cloverleaf interchange
November 25th, 2011
I don’t understand any of this, but it reminded me of this musical score…
http://lostinthecloud.files.wordpress.com/2010/03/faeries-aire.gif