2818: Circuit Symbols

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Circuit Symbols
A circle with an A in it means that the circuit has committed a sin and has been marked as punishment.
Title text: A circle with an A in it means that the circuit has committed a sin and has been marked as punishment.


This comic contains several symbols used in circuit diagrams. Each is labeled with a larger object that the symbol looks like a drawing of, rather than the electrical component it actually represents. Randall has previously depicted distorted uses, depictions, and labeling of the standard US-form electronic symbols in comics such as 730: Circuit Diagram.

Symbol Randall's Description Explanation
Switch Drawbridge The symbol represents a physical on/off switch in a circuit, but also resembles a drawbridge. A switch functions the exact same as a drawbridge, impeding electrons' flow when it is open. The purpose of a drawbridge is to allow people to cross who are impeded when the bridge is raised.
Capacitor Overpass A capacitor is a component that can be used to hold electric charge, but the symbol for it looks a bit like a depiction of a highway overpass, where one road or track passes over another, allowing the paths to cross without intersecting. The distinction between an overpass and underpass is largely one of perspective, as when one road (or footpath, or animal migration route) goes over, the other is going under. Because a capacitor does not indicate a place of intersection of separate electrical circuits, any interpretation of a meaningful connection between an overpass and a capacitor is tenuous at best. A capacitor is an electrical component that alternating current can get across, but direct current can't. This could be like how heavy trucks are not allowed on overpasses. However, this still only involves one electrical pathway.
Ground Pogo Stick This symbol represents a connection to "ground" or "earth", the common baseline voltage or safe current sink for various circuits (e.g., against which an aerial signal can be compared). If the horizontal lines are taken as motion lines or a spring, it might look like a stylized pogo stick.
Resistor (ANSI) Earthquake A resistor is a component that reduces current flow in a circuit. There are two main symbols used: an IEC-style 'box' or, like here, the ANSI zig-zagged line. In this case, it also looks somewhat like the marks an earthquake makes on a seismograph and/or the 'rucks' of the ground (especially asphalt roads) that might result from underlying tectonic movements.
Inductor Sheep Inductors create a magnetic field when current passes through them, and generally consist of a coil of wire, which the symbol reflects. The symbol seems in this case to be interpreted like the fluffy wool of a sheep.
Transformer Two sheep in love, trapped on opposite side of a fence. A transformer consists of two (or more) induction coils, for input and output(s), and a common core to mediate the transfer of power across the gap. The curly loop symbols of the symbol have already been claimed to resemble sheep, and the straight line (which is the core) now represents a fence separating two sheep who nonetheless wish to be together.
Battery Battery Not a joke, this is a typical symbol for a battery (which provides voltage to a circuit[citation needed]), or other form of voltaic pile. Its inclusion here is simply as the set-up for the following joke symbols.
Battery (sorted) Baertty Randall may have mapped the characters "tt" to the first short line and "er" to the following long line in the original symbol, having had "ba" and "y" assigned to the long and short "T" shapes that form the connections to the rest of the circuit. Rearranging the symbolic verticals as long-long-short-short, as he has done in this (fictional) symbol, thus puts "er" in front of "tt". Another sorting paradigm is that, after the initial 'B', the remaining letters are arranged in alphabetical order, left to right. Similarly, after the first horizontal line in the symbol, the other line segments are arranged by decreasing vertical height (left to right).
Battery, with far too many short lines Battttttttttttery The only other fictional symbol. Which, by the same established naming rules, means that the name is spelled with six "tt"s instead of just the single pair.
Photodiode Check out this really cool diode A photodiode generates, or allows to pass, a current in response to light. The symbol is related to the standard diode with the arrows pointing at it representing the light which activates its behavior. In this case, Randall instead pretends that the arrows are pointing at it to draw attention to it because it's "really cool".
Oscillator Wave Pool An oscillator generates signals that oscillate at a given frequencies, for use in other circuitry, and one symbol used for one (in reality, built from a number of components in their own right) is this symbol. Waves in water are a type of oscillation that may be more familiar to most people than waves of electricity. A wave pool is in fact the result of a type of (mechanical) oscillator, and rarely has electricity running through it.[citation needed]
Transistor Trolley Problem A transistor will switch on current flow across one of a pair of connections, depending upon the input from an input one. Randall likens this to the ability to use points to switch the destination of a trolley from one track to another, as protagonists are invited to do in the various versions of the trolley problem. The symbol also somewhat resembles the usual pictorial depiction of the problem. However, single transistors are not generally used to resolve ethical dilemmas.[citation needed]
A circle with an A [In the title text] The circuit has committed a sin and has been marked as punishment Circles with letters are usually some special components, as also with the oscillator's glyph. In this case the "A" stands for ammeter, a device used to measure electric current (an "ampere meter"). This is conflated with the practice of branding the 'guilty', or requiring them to display their crime for a period of penance. For example, in The Scarlet Letter, a historical novel by Nathaniel Hawthorne, the protagonist must wear an A to mark her as an adulteress.


[A chart of various circuit symbols and their (mostly) fictitious meanings based off of their drawings, captioned:] Circuit Symbols
[Symbol for a switch, labelled:] Drawbridge
[Symbol for a capacitor, labelled:] Overpass
[Symbol for a connection to ground, labelled:] Pogo Stick
[Symbol for a resistor, labelled:] Earthquake
[Symbol for an inductor, labelled:] Sheep
[Symbol for a transformer, labelled:] Two Sheep in Love, Trapped on Opposite Sides of a Fence
[Symbol for a battery, labelled:] Battery
[Symbol for a battery, sorted, labelled:] Baertty
[Symbol for a battery, with far too many short lines, labelled:] Battttttttttttery
[Symbol for a photodiode, labelled:] Check Out This Really Cool Diode
[Symbol for an oscillator, labelled:] Wave Pool
[Symbol for a transistor, labelled:] Trolley Problem

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The direct link to the comic is getting a 404 error. But it appears at the xkcd.com home page. Barmar (talk) 01:31, 22 August 2023 (UTC)

The link is working now. Nitpicking (talk) 02:33, 22 August 2023 (UTC)

Randall is symbolizing sheep with a coil because ... wool takes a helical shape. See https://commons.wikimedia.org/wiki/Wool#/media/File:Royal_Winter_Fair_Wool.jpg. Nitpicking (talk) 02:33, 22 August 2023 (UTC)

I think it's meant to be a little prince reference; it's a "box with three holes" 06:07, 11 December 2023 (UTC)

The title text is probably a reference to the classic novella "The Scarlet Letter" by Nathaniel Hawthorne (a common classroom reading in the US). In this novella, a young Puritan woman "sins" by having a child out of wedlock. She is punished by having to wear the letter A (for adultery). Comsmomf (talk) 02:54, 22 August 2023 (UTC)

Can someone with more wiki-foo than me please put the actual images for the symbols in a new first column? Blackbearnh (talk) 03:01, 22 August 2023 (UTC)

The easy way to do this might be with the SpriteSheet extension, but maybe that's more trouble than it's worth. Any admin thoughts about installing it? JohnHawkinson (talk) 02:22, 25 August 2023 (UTC)

I tried, unsuccessfully, to learn if there were "Scarlet Letters" that represented other sins ['A' is mentioned to be for 'Adultery', Maybe 'O' for Onanism?] These Are Not The Comments You Are Looking For (talk) 03:41, 22 August 2023 (UTC)

From what I understand, ‘BJ’ had its fair share of supporters. 04:47, 22 August 2023 (UTC)

What exactly does "the opposite of capacitors" mean in this context? I'm not that familiar with EE, but from my limited understanding of inductors this is an incorrect and confusing statement. 08:07, 22 August 2023 (UTC)

They are the conjugate complex (so the sentence is kind of half-true), if you consider complex impedances. Sebastian -- 08:56, 22 August 2023 (UTC)
Behaviorally the description makes sense, capacitors behave the same way regarding voltage vs. current as inductors behave regarding current vs. voltage and vice versa. Capacitors can "instantaneously" allow a spike in the current flowing through the circuit path that they are placed in, while the voltage across a capacitor can't change instantaneously and requires time to change incrementally (with a corresponding decline over time in the current flowing). Inductors "instantaneously" allow the voltage across their terminals to spike, but the current flowing through it can't change instantaneously and requires time to change incrementally (with a corresponding decline in the voltage across the inductor). Capacitors can act as a sort of "shock absorber" (no pun intended) or low-pass frequency filter for voltages, as inductors can for current. So they are very much considered complementary and the "essentially the opposite of capacitors" comment does pretty much make sense to EEs. But yes, it's not a particularly illuminating description without that background, and the description isn't really valid regarding their physical makeup or what makes them tick, just their role in a circuit. 09:32, 22 August 2023 (UTC)
Incapacitors 16:48, 25 August 2023 (UTC)

The "overpass" is troubling me, as a map fan. Dependant upon the conventions of any given map illustrator this could easily be more an underpass (main road being the || track, lesser track being the — that sneaks beneath it) or a 'green bridge' (road is the — and the bridge 'symbol' is the || with no actual route using the space between its edges) or a minor road intersection of an uncrossable dual carriageway (each || is a directional way, separated by central reservation, and a historic road/lane is given T-junction access to/from the adjacent direction of travel, but no local flyover to access the opposite continuation/direction, probably have to use other flyovers/turning points above and below this snapshot). Or it's just a regular major/minor crossroads (track-level horizontal/E-W, more main road vertically/N-S) and is entirely at-grade so not involving a bridge at all. But all very much will rely upon the publisher's/renderer's choice of map-symbolism. 11:27, 22 August 2023 (UTC)

What's your hope? That Randall will edit his comic? -- Dtgriscom (talk) 11:41, 22 August 2023 (UTC)
No more than I wish he'd use IEC resistors rather than the US zigzags. Just highlighting that (in isolation) there's so easily an alternate inference, dependent upon what notation/symbology you're most exposed to. 16:36, 22 August 2023 (UTC)
I appreciated the map trivia, personally Dextrous Fred (talk) 15:18, 22 August 2023 (UTC)
Cheers, though I can't help but think that I explained it badly. And without much reason to. 16:36, 22 August 2023 (UTC)
I added the joke about needing a citation-needed joke. Please remove if you don't feel it was needed after all.
Where I live the distinction between underpass and overpass is more about whether the bridge is at grade, and excavation has been done for the other road to pass under (i.e. under the ground level) or the bridge is above grade and the road it crosses over is at grade. -- 11:28, 25 August 2023 (UTC)
From my perspective, you also need to consider flyovers (bridges rising above grade, usually more minor or singular carriageways compared to the at-grade main road with or without median-separated carriageways). If the main route rises over the minor (which remains at-grade, more or less) with clear over-ground construction, it's just a road-bridge. An underpass need not be subterrainean, and often can be an at-grade "original" route (typically pedestrian) beneath the embankmented new major road (or other route, e.g. rail) that was engineered across it, in the same subtle manner as a culvert. Or even what you'd now term the stretch of road "bridged" (or tunnelled) beneath the building of a cross-highway shopping centre, like some towns do in order to sustain an inner ringroad and a large footprint shopping centre.
In general, if the 'over' road doesn't really notice the 'under' (it's still mostly the same grass verging, maybe briefly slightly higher crash-barriers on top of whatever embankment-guarding barriers already exist but no clear 'bridge' details) then I'd just name the underpass as such, as everything on that is definitely going to know that it is diving under the upper route
It can be complicated. The extended runway seen here is possibly at-grade overpass, w.r.t the whole airport "level" (equivalent to a by-pass embankment?), while the road looks sunken (as can be seen by how much the pedestrian side-portal need not be). It could be a runway on an overpass, though I'd say the road is an underpass (with a possible argument that it was always a cut'n'cover tunnel, or passing under really long bridge). 17:46, 25 August 2023 (UTC)

With a capacitor you can build a low-pass filter. It can be used in signal processing like audio devices to filter out noise. 21:01, 22 August 2023 (UTC)

I think the Battery/Baettry/Batttttttttery joke is probably a reference to the oreo/oreoreo/etc meme that can be seen at https://i.kym-cdn.com/photos/images/original/001/839/727/d7f.jpg . 13:58, 23 August 2023 (UTC)Bumpf

Feel free to add that to the page! --FaviFake (talk) 20:44, 23 August 2023 (UTC)
To me the last one sounds like hoe Metallica sings battery in the song ‘Battery’

The electricity in a wave pool citation needed is the first properly funny one I've seen in quite a while - I approve. 16:49, 25 August 2023 (UTC)

The capacitor explanation is a bit of a mess at the moment, with pronouns lacking any apparent referent. I'm going to clean it up to the best of my ability, but since I only know things from the civil engineering side and not the electrical engineering side, it will almost certainly need someone who actually understands capacitors to give it a once or twice over. 15:55, 29 August 2023 (UTC)

I'm surprised that NPN transistor was used for the Trolley Problem instead of PNP. It would make a lot more sense because the PNP symbol has an arrow pointing towards the center, which corresponds nicely with the trolley heading towards a fork. Bebidek (talk) 21:19, 24 May 2024 (UTC)