[gta02-core] Values and units in schematics

Werner Almesberger werner at openmoko.org
Wed Jul 1 03:32:55 CEST 2009

Rene Harder wrote:
> or we could use 0R+j4R7 @100Hz for an inductor (ideal)  :-D

Oh, just attach the complete SPICE model and shrink the font to
make it all fit into 60 mil ;-)

> The problem with using uncommon notations is that you need to study the
> definitions first before you can read the schematics,

Sure, but 1200U isn't all that uncommon. I even Digi-Key use
only increments of six orders of magnitude for things as basic
as capacitors. Not that I particularly enjoy looking up 100 nF
capacitors there - "10000pF" has an awful lot of zeroes ...

But yes, I understand your point. If you're looking for "100 nF"
then everything that isn't 100-something can be confusing.

> You said it will improve readability, does it really increase readability?
> I never had any problems with seeing the difference between 1n2 and 1u2

Hmm, maybe it's just me, but I noticed that 10 nF/10 uF left me
with a doubt if I had seen the prefix properly. It's not an issue
of not being able to read it, but one of seeing what one expects
to see when giving it a quick glance.

But perhaps it's not so bad in the end ... your schematics with
lower-case units certainly are readable enough.

So ... "simple components" (resistors, capacitors, and inductors):

- one mixed-case letter per value, serving as decimal point,

- where that letter is a unit, no space between number and unit,

- secondary attributes like tolerance (1%), material (X5R), or even
  ESR (50 mOhm - there we have it ! :), don't make this a complex

Complex, multi-valued units:

- use regular SI notation (5.6Vac), except
- no space between value and unit

How does this sound ?

- Werner

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