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The use of 3V3 and 1V8 can be seen in several posts here and in the recent Raspberry Pi video Introducing the Raspberry Pi 3 Model B+. I've spotted 1k8 as a resistor value in a few places (e.g. here and here) as well.

In another site the recent meta question Ways to indicate decimal and thousands demarkations...? resulted in an interesting and well-received answer, so I thought I'd ask for a quick run down of this electronics notation here as something that can be pointed to again if the subject ever comes up.

  • I was looking for something like a terminology tag, so far no luck. – uhoh Dec 25 '18 at 11:59
  • Is this meta site the best place for this question? Most meta posts here are about the site's policies and supporting users with how to use the SE software. This might work better on the main site along the lines of "What does 3V3 mean on this Raspberry Pi schematic?" (for example), and there is also a question on Electrical Engineering which covers essentially the same ground. – Aurora0001 Dec 25 '18 at 16:46
  • @Aurora0001 I can modify the question to "is it okay to use notation like 3V3, 1V8 and 1k8 in this site?" and adjust the wording of the body slightly to match. That would require only minimal adjustment to @Ghanima♦'s answer, but make the question more meta-like. Would that address your concern? – uhoh Dec 25 '18 at 23:08
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It's actually quite simple... once you know it.

3V3 means just 3.3 V, same goes for 1V8, so it's really nothing more than a shortcut. Dropping the decimal separator and use the unit instead. Safe a character or two.

1k8 is likely referring to a resistor, its resistance being 1800 ohms or 1.8 kOhm. So again, while horrible in a physicist's eye, a simple short notation only. In schematics the components, i.e. the resistor, can be clearly identified by its symbol, thus you already know that its characteristics will be measured in ohms, no need to repeat the unit in writing. Not to mention that in ancient times there was likely no "ohms" character in the limited character table... and in it were it would still print out wrong on a different system. Same goes for inductors and capacitors, e.g. you will find capacitors labelled with "100 n" when referring to a 100 nanofarad cap.

In real life dropping all unnecessary characters might have proven necessary when printing electronic components, well at least back in the olden days when these components still had a significant surface to print on.

There is probably a question to that end on the electrical engineering stack.

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