Author Topic: Modern way to specify values on schematics  (Read 6181 times)

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Online ebastler

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Re: Modern way to specify values on schematics
« Reply #25 on: March 05, 2019, 09:23:59 am »
I prefer 0R47, 100, 1k, 2k2, etc. for resistors, 2p2, 330p, 4n7, 68n, 2µ2, 10µ, 3300µ for capacitors, and 150n, 2µ2, 330µ, 15m, 10H for inductors.

The "10H" is the odd one out in that list. Any particular reason why you include the unit there, and only there?
 

Offline AndyC_772

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Re: Modern way to specify values on schematics
« Reply #26 on: March 05, 2019, 09:47:39 am »
I think the inconsistency there is that "100" (resistance) has no unit; I'd use 100R.

Online Zero999

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Re: Modern way to specify values on schematics
« Reply #27 on: March 05, 2019, 10:04:30 am »
I am a Texan (Remember the Alamo!), so it pains me to say this...Europeans got it right with the metric system and with the comma.  It is the right thing to do.  :phew:
I agree about the metric system but using commas vs full stops for decimal places seems arbitrary. In the UK we use the . for the decimal place and , for the separator, which only looks right to me because it's what I'm accustomed to. I think the . or , is fine for the decimal place but to avoid confusion only the space or ' should be used for the separator.

And do not use 'm' for micro.  I use 'm' for milli and 'u' for micro.
I tend to avoid using milli farads for that reason, so 1mF should be written as 1000µ. For larger values it starts for make sense to use farads, so 10 000µF becomes 0.01F, which in theory could be 0F01, but that would confuse lots of people.
 

Offline jpanhalt

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Re: Modern way to specify values on schematics
« Reply #28 on: March 05, 2019, 10:41:22 am »
Interesting how so many feel they are using the SI system, often called the metric system, but don't follow its rules.

Source: https://www.nist.gov/pml/weights-and-measures/writing-metric-units
Rule(Spacing):
"A space is used between the number and the symbol to which it refers. For example: 7 m, 31.4 kg, 37 °C."

In any event, as for schematics or any published work, it is far more productive just to get the "Instructions for Authors" and follow them than to try to argue with an editor.

Such cultural things as 9R1 versus 1n0 seem inconsistent, but common.

 

Online ebastler

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Re: Modern way to specify values on schematics
« Reply #29 on: March 05, 2019, 11:47:25 am »
Interesting how so many feel they are using the SI system, often called the metric system, but don't follow its rules.

You are confusing the SI system of units with the typesetting rules for writing numbers and (whichever) units.
 

Offline jpanhalt

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Re: Modern way to specify values on schematics
« Reply #30 on: March 05, 2019, 12:14:27 pm »
Interesting how so many feel they are using the SI system, often called the metric system, but don't follow its rules.

You are confusing the SI system of units with the typesetting rules for writing numbers and (whichever) units.

I wrote SI "system."   That system defines printing format among many other things.  No confusion on my part.  Here is a link to a primary source: https://www.bipm.org/en/publications/si-brochure/
 
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Offline bitbanger

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Re: Modern way to specify values on schematics
« Reply #31 on: March 05, 2019, 12:23:34 pm »
This somewhat humorously reminds me I once use the R separator in a project (i.e. 47R) I was worried about distiller/render compatibility issues and the ohm symbol. My supervisor at the time lost her mind over it, "we just don't do that here".   ;D
 

Offline Wimberleytech

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Re: Modern way to specify values on schematics
« Reply #32 on: March 05, 2019, 01:37:34 pm »
I follow a few rules:

1. Never use a decimal point. Sometimes it doesn't show up, and is easily missed. In place of the decimal point, use the magnitude. Try to avoid leading zeros if possible.

BAD: 1.2k
GOOD: 1k2
BAD: 0.1u
GOOD: 0u1
BETTER: 100n

2. Never use the unit, only the magnitude, EXCEPT when the magnitude is unity. This is just practical, because you really don't want to use any more space than you have to. The schematic symbol itself shows you what the component is. Resistances are always in ohms, capacitances in Farads, inductances in Henries. For ohms, use "R".

Corollary to #2: I prefer to use the IEC symbol for resistors, which is a rectangle. The value goes inside the rectangle instead of next to the symbol.

BAD: 1kΩ
GOOD: 1k
BAD: 1.2Ω
GOOD: 1R2
BAD: 22pF
GOOD: 22p

3. Never use the micro character. Instead, use "u".

BAD: 22µ
GOOD: 22u


As for the question about resistor values, the primary purpose of a schematic is to convey information, so it needs to be as visually pleasant as possible. Lines which cross every which way are bad. Even multiple parallel lines for a bus isn't great, use a thicker bus line instead. Signals should generally flow from left to right. Use subsystems if things get too busy.

So, if adding component values would clutter up the diagram, it's reasonable to put them in a table off in the corner. Use notes to explain the values.

Ditto...and NEVER USE FOUR-WAY CONNECTIONS.  NEVER USE DOTS to indicate a connection.
 

Online ebastler

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Re: Modern way to specify values on schematics
« Reply #33 on: March 05, 2019, 03:19:43 pm »
I wrote SI "system."   That system defines printing format among many other things.  No confusion on my part.  Here is a link to a primary source: https://www.bipm.org/en/publications/si-brochure/

Thanks, I learned something new!
I will limit my claim to "I am using SI units" going forward.  ;)
 

Online ebastler

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Re: Modern way to specify values on schematics
« Reply #34 on: March 05, 2019, 03:22:51 pm »
NEVER USE FOUR-WAY CONNECTIONS.  NEVER USE DOTS to indicate a connection.

I agree with the "no four-way junctions". But for three-way junctions, don't pretty much all CAD systems use dots to indicate junctions, and don't DIN, IEC etc. require them in schematics?
 

Offline Richard Crowley

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Re: Modern way to specify values on schematics
« Reply #35 on: March 05, 2019, 03:38:28 pm »
Corollary to #2: I prefer to use the IEC symbol for resistors, which is a rectangle. The value goes inside the rectangle instead of next to the symbol.
The problem with that rectangle is that it is confusingly overloaded. If ONLY resistors used the rectangle, OK. But there appear to be half a dozen different components that use the same rectangle (or a slight variation).  Maybe it is a resistor, but there are some places where maybe it is a fuse.  Or an inductor,  or ????

I grew up reading the schematics in Popular Electronics here in the US and that was always my reference for nice design.
 

Online Zero999

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Re: Modern way to specify values on schematics
« Reply #36 on: March 05, 2019, 04:22:36 pm »
Interesting how so many feel they are using the SI system, often called the metric system, but don't follow its rules.

Source: https://www.nist.gov/pml/weights-and-measures/writing-metric-units
Rule(Spacing):
"A space is used between the number and the symbol to which it refers. For example: 7 m, 31.4 kg, 37 °C."
Probably because it's a stupid rule.

There are also other stupid things such as kg for the base measurement of mass and µ, for micro, which isn't found in all fonts, but u is generally accepted because it's close enough.
 

Offline level6

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Re: Modern way to specify values on schematics
« Reply #37 on: March 05, 2019, 04:30:35 pm »
NEVER USE FOUR-WAY CONNECTIONS.  NEVER USE DOTS to indicate a connection.

I agree with the "no four-way junctions". But for three-way junctions, don't pretty much all CAD systems use dots to indicate junctions, and don't DIN, IEC etc. require them in schematics?

I also thought dots are required for junctions  (not talking about 4 way junctions). Eagle adds them in by default when connecting nets.
« Last Edit: March 05, 2019, 10:59:18 pm by level6 »
 
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Offline Wimberleytech

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Re: Modern way to specify values on schematics
« Reply #38 on: March 05, 2019, 07:31:57 pm »
NEVER USE FOUR-WAY CONNECTIONS.  NEVER USE DOTS to indicate a connection.

I agree with the "no four-way junctions". But for three-way junctions, don't pretty much all CAD systems use dots to indicate junctions, and don't DIN, IEC etc. require them in schematics?

I also thought dots are required for junctions. Eagle adds them in by default when connecting nets.

As long as four-way connections are NOT allowed, then dots are redundant.  I am ok with a redundant dot...a pacifier dot.  CAD systems are self checking so they won't make errors confusing crossovers with connections.  But drafted schematics are notorious for this problem.  I have reviewed many thousands of schematics in journal papers and patents.  I see this issue all the time.  Been awhile since I drew a schematic in Cadence, but pretty sure that tool does not allow four-way connections.  Cannot speak for Eagle.
 

Offline kuonTopic starter

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Re: Modern way to specify values on schematics
« Reply #39 on: March 06, 2019, 11:42:35 pm »
Thank you so much for all your insight.

I have switched to this system https://www.eevblog.com/forum/beginners/modern-way-to-specify-values-on-schematics/msg2238423/#msg2238423 . The arguments makes the most sense to me and I can understand it.
 

Offline bson

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Re: Modern way to specify values on schematics
« Reply #40 on: March 07, 2019, 12:21:22 am »
Use either period or comma, it doesn't matter which.  Use SI prefixes for 1000s.  Don't use the metric 10 and 100 prefixes (centi, deci etc).  Don't use a space or any other separator for 1000s, keep it simple.  Spell out units other than Ω, simply because some software still has problems with UTF.  Or, use it if you like - it's rarely a problem.  Or skip the units altogether if it's obvious from the component.  It doesn't terribly matter.  The SI m means milli and nothing else.  If you're concerned with UTF and reproducing µ, then use u.
 

Offline bsfeechannel

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Re: Modern way to specify values on schematics
« Reply #41 on: March 08, 2019, 04:38:34 am »
I prefer 0R47, 100, 1k, 2k2, etc. for resistors, 2p2, 330p, 4n7, 68n, 2µ2, 10µ, 3300µ for capacitors, and 150n, 2µ2, 330µ, 15m, 10H for inductors.

The "10H" is the odd one out in that list. Any particular reason why you include the unit there, and only there?

Because in some old schematics, inductors with unit values would be considered nH or µH.
 
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