Prototyping Values for Unpopulated Bypass Caps?


#1

I’m looking at a schematic for a board that I had done a few months back. I remember now that I had added two capacitors into the design that I did not populate prior to testing.

I figured that instead of dead-bug construction I’d have these two Land Patterns available to use for testing.

At the moment, I’m tempted to label the value of these caps as “Proto”.

Anyone else have an alternative that is best practice?


#2

We documented unknown values as “TBD” aka “to be determined”. I don’t know of a specific “best” practice. I was always a fan of adding notes to anything that was not absolutely clear.

I’ve also seen components annotated as “for future use”. Again this would be in a note.


#3

I’m pretty familiar with things not being clear. However, I am starting to see the benefit of more documentation instead of less.


#4

One note I often add identifies components (usually capacitors or inductors) included for EMC. Folks down the road might be temped to change something without fully understanding their function.


#5

“Reserved” and “Select at test” are also common phrases.

It’s not unusual to design two or more variations of a board, with different values for some components. (The classic example, before the creation of wide-range or auto-ranging power supply designs, was a board that would be manufactured in one variation for 120V mains and a slightly different variation for 220V mains.) The different values are typically spelled out in a “Note” or “Table of Values” on the schematic, or sometimes on the parts list. On the schematic the part itself has a value of “See Note xx”, “See Table”, or “See P/L”.

Dale


#6

“NC” for No Connect.
“TP1”, “TP2” for test points 1 & 2.


#7

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