I'm new to circuit design and reading schematics but have a little familiarity there. On this diagram which shows a circuit built on a strip board, I don't quite understand the meaning of the red-outlined white square that contains a red dot.
Electronic – the red-outlined white square that contains a red dot in this diagram
diagramstripboard
Related Solutions
First of all, this is a nonstandard and unhelpful way of calling out component values. Don't do this on schematics you draw! (In normal practice, "R220" means "resistor number 220" and the value is shown separately.)
But somebody with experience might be able to figure it what's going on. Let's see how I do...
C180 must mean 18 pF. Those are crystal load capacitors, which are commonly in the 10 pF - 20 pF range.
C105 means 1 uF. These are bypass capacitors and 1 uF is a common value and the datasheet-recommended value.
R220 probably means 22 ohms, from the example circuits in the 32u2 datasheet.
I found this drawing in the datasheet:
Also notice the supply connections. The micro has its own internal regulator, so the Vcc doesn't need to be connected to anything else (except its bypass capacitor.)
None of the components are super critical. 10% tolerance should be fine.
Once again, don't use this as example of how to draw schematics.
(edited to revise 0.1uF guess to 1 uF.)
I've been working professionally as an engineer for over 20 years now and can say that while there is no single dominant application for creating block diagrams, the one I see used more than any other is Visio. In addition to hardware engineering, the tool is also widely used by network engineers--to the point where companies like Cisco create stencils for it.
The caveat here is that Visio a windows only tool. Though being that you're BootCamp perhaps that's not a show-stopper.
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Best Answer
I'd guess that the red dot and square indicate a cut in the copper track - there should be no connection between the track sections to the left and right of that symbol. (but it would be nice to have a schematic of that circuit to verify my guess)