I know that the reason why the North American resistor symbol is just squiggly lines because that is how the electrons flow (due to the way how resistors are made), but why is the European resistor symbol a box shape. Also there is a reason why capacitors have two lines separated, but why does one valid schematic symbol have a curve? For integrated circuits, the pinout given in datasheets match the physical layout, but some schematics editors have multiple ways to represent one integrated circuit? Can someone explain that?
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- 8\$\begingroup\$ This is a little like asking "Why are there different languages?" or "Why are there different cultures?" Some engineering notation occurs because of cultural or language differences, or differences in various company policies, and not all of these evolve and change at the same rate. \$\endgroup\$JYelton– JYelton2024-12-17 22:36:43 +00:00Commented Dec 17, 2024 at 22:36
- \$\begingroup\$ I really don't get why the European resistor is a box shape, is it because of the way it looks or is it something else? \$\endgroup\$SnappyRiffs– SnappyRiffs2024-12-17 22:39:46 +00:00Commented Dec 17, 2024 at 22:39
- \$\begingroup\$ also what do you mean by "Some engineering notation occurs because of cultural or language differences" \$\endgroup\$SnappyRiffs– SnappyRiffs2024-12-17 22:40:50 +00:00Commented Dec 17, 2024 at 22:40
- 4\$\begingroup\$ a curved line on a capacitor indicates it has a polarity (ex electrolytic), so there's one mystery solved. \$\endgroup\$dandavis– dandavis2024-12-17 22:46:36 +00:00Commented Dec 17, 2024 at 22:46
- 5\$\begingroup\$ @SnappyRiffs a blog post on a store website hardly seems authoritative. I can find typos and misspellings everywhere, that doesn't mean they are valid or alternative spellings. There are widely-held conventions. \$\endgroup\$dandavis– dandavis2024-12-17 22:50:52 +00:00Commented Dec 17, 2024 at 22:50
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2 Answers
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11 I know that the reason why the North American resistor symbol is just squiggly lines because that is how the electrons flow (due to the way how resistors are made),
Ehm, no. The zig-zag line is a graphical representation of a wirewound resistor wrapped around some sort of former. This was how resistors were originally made.
Why is the European resistor symbol a box shape.
It's a simpler symbol to draw with a pen and stencil which is the way things were done before CAD.
Also there is a reason why capacitors have two lines separated,
Yes, it's a symbolic representation of two conductive plates separated by an insulator (which may be air).
but why does one valid schematic symbol have a curve?
To signify that it's polarised. The curved side is negative.
For integrated circuits, the pinout given in datasheets match the physical layout, but some schematics editors have multiple ways to represent one integrated circuit? Can someone explain that?
Sure. When drawing schematics it's important to communicate the schema or design intent of the circuit. Generally we try to lay out the schematic so that signal flow is from left to right and power supply current flows from top to bottom.
The chip designer has a whole other set of problems to contend with so the pinout may not make much sense to the casual observer.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Two representations of a dual op-amp.
Which of the above representations of the dual op-amp shows the schema more clearly?
- \$\begingroup\$ for more experiecned people, i think b would be more appropiate, but for a non-experienced person (or someone who wants to view the op-amps at a clearer way), a would be more appropiate \$\endgroup\$SnappyRiffs– SnappyRiffs2024-12-17 22:50:38 +00:00Commented Dec 17, 2024 at 22:50
- 17\$\begingroup\$ (a) might be useful to someone wiring up a chip with no understanding. (b) would be far superior for anyone wanting to understand the circuit or for fault finding. \$\endgroup\$Transistor– Transistor2024-12-17 22:53:23 +00:00Commented Dec 17, 2024 at 22:53
- \$\begingroup\$ ICs that mimic/contain pre-existing components inherit thier older symbols, like an op amp, whereas an, ex, AT tiny MCU IC has no "traditional" symbol. \$\endgroup\$dandavis– dandavis2024-12-17 22:55:16 +00:00Commented Dec 17, 2024 at 22:55
- \$\begingroup\$ For something like the raspberry pi rp2040, I've seen a weird way of drawing it (aka the pins aren't in order, but theh datasheet shows the typical IC schematic(aka pin 1 on top left and the last pin on the top right)) \$\endgroup\$SnappyRiffs– SnappyRiffs2024-12-17 22:57:28 +00:00Commented Dec 17, 2024 at 22:57
- 2\$\begingroup\$ Even unpolarized capacitors have a curved symbol; it denotes the external metal of a case and ought to guide assemblers to minimize AC signal leakage to nearby components. Electrolytic capacitors often have a negative terminal to the case; for positive power filtering, that's 'ground'. \$\endgroup\$Whit3rd– Whit3rd2024-12-18 01:58:37 +00:00Commented Dec 18, 2024 at 1:58
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I know that the reason why the North American resistor symbol is just squiggly lines because that is how the electrons flow (due to the way how resistors are made), but why is the European resistor symbol a box shape.
Some resistors are made that way (that is, wirewound). But the squiggly shape is meant to convey the idea that a resistor 'slows down' current flow by making a longer winding path than a straight wire, much like a chicane in a race course slows down the cars.
That squiggly line graphic, while descriptive, presents problems in a schematic. It often gets smudged into something unrecognizable, especially when a drawing gets reproduced on a smaller sheet than its original. Also, it’s tedious to draw by hand, especially so considering how often resistors show up in schematics.
The 'European' style rectangle box shape is easier to draw, it reproduces better (think blueprint or multiple generations of photocopy), and doesn't disappear when a drawing is shrunk down. Early in my career I adopted it and never looked back.
Also there is a reason why capacitors have two lines separated, but why does one valid schematic symbol have a curve?
The different plate shapes indicates polarity - kind of. A polarized cap is supposed to have the curved plate for "-" (cathode) and straight for "+" (anode.) A non-polarized cap has two straight plates.
However, the curved-plate's polarity purpose has been sullied over time. You’ll find it's also been widely used for non-polarized caps, too (it’s often the default CAD symbol.)
As a consequence, to mitigate confusion, drawings have adopted a "+" (anode) marking for polarized caps, regardless of whether the cap symbol has the curved anode or not.
More here: https://www.nextpcb.com/blog/capacitor-symbol
What does a standard say about this? See here, pp. 24. The tl, dr: the curved plate is the 'outside' of the cap or a terminal meant to be at lower potential, such as the body of a motor start cap or a feed-through cap.
For integrated circuits, the pinout given in datasheets match the physical layout, but some schematics editors have multiple ways to represent one integrated circuit? Can someone explain that?
It's a combination of clarity, preference and practicality.
ICs with multiple devices like gates and op-amps benefit from splitting them off as individual functions, so that the finished drawing can better convey the signal flow. For example, a quad op-amp like the LM324 will be represented as four sub-instances as UxxA / UxxB / UxxC / UxxD. The drawing will have each op-amp by itself, with its corresponding circuitry. This makes it much easier to grasp the function of each one than if the op-amps were smooshed together.
Some drawing styles show multi-instance parts as whole packages (think Sams Photofact or Tinkercad), which some technicians and learners favor over separate symbols. For small ICs like that quad op-amp this might be ok or even considered useful. For big ICs this becomes cumbersome: you just get a box bristling with pins.
Speaking of which, high pin count ICs like FPGAs, microprocessors and the like are completely impractical to draw as a single symbol. These require breaking up into multiple blocks, sometimes spanning many schematic pages for a really huge part.
On the other hand some complex ICs like memories have few enough pins that they can still be a single block, with the pins arranged by function to better convey signal grouping and flow.
What about IEEE Style?
In the heyday of small- and medium-scale logic, there was an attempt to harmonize a drawing system that represented function. And that attempt culminated in IEEE 91-1984, which some derisively observe makes logic parts all look like TO-220 transistors.
I'll go a step further than that. ‘IEEE’ style is the Esperanto of the schematic world. A lot of thought went into its design, yet it was obsolete the day it came out. By then big LSIs had largely supplanted SSI and MSI logic. (How would you represent, say, a 68000 in IEEE style? You don't, it's a box with pins.) IEEE style is fiddly to draw by hand. It only made sense for CAD which at the time (mid-80s) was reserved for well-funded design centers.
As a consequence most people rejected it at the time. You won't see it in a newer schematic.
