Schematic Drafting Standards

[nctnico]

means never having a schematic symbol which has all the pins in the same position as the component

Hey now! There was that one, one!, time where the IC guys laid out the pinout perfectly! Once... maybe twice... in all these years... that was a nice project, I miss that part....

No, but seriously, never do this. One of my tells for low-quality schematics is when schematic pin arrangement matches the part physical pin arrangement. Nothing good comes of this.

Well, I assume you never debugged / verified a circuit then. In reality it greatly depends on the part whether it is feasible to draw the part like it is in the schematic. If you can, do draw the part as it is. When doing debugging / verification, all you need to know where to place a probe is the schematic and no need to count pins as you can tell by the external arrangement of the components which pin is which  in many cases. This saves a lot of time (which equals money).

Another good reason to draw a part in its physical form is that you have a good overview whether all pins have been assigned.

Actually, if the schematic looks like a mess when you draw a part in its physical form, the part is likely going to be a nightmare to get routed on the board anyway. So this is a good first sign of how difficult the board layout is going to be. Maybe a different part is more suitable.

Absolutely not! What on earth does "draw the part as it is" mean?!

The purpose of the schematic is to expose the design. That guides understanding what you should observe when you place a probe on a component.

Yes, the purpose of the schematic is to lead to something which is useful. And hence you grossly glossed over the 'it depends' part and the part based on very extensive hands-on experience that -if possible- drawing a part like it sits on a PCB is super immensly helpful to make a schematic actually useful. You seem to keep on wanting to create schematics like abstract art which at some point nobody understands. I for one don't want to be like Picasso in his abstract period; I want people to understand and use my schematics without needing any other documentation as much as possible. This all starts by very carefully choosing how to represent parts in a schematic. But also adding notes, expected voltages, etc. And for more complex circuits things like a block diagram, power-trees, power sequencing, power usages, currents, etc.

[16bitanalogue]

means never having a schematic symbol which has all the pins in the same position as the component

Hey now! There was that one, one!, time where the IC guys laid out the pinout perfectly! Once... maybe twice... in all these years... that was a nice project, I miss that part....

No, but seriously, never do this. One of my tells for low-quality schematics is when schematic pin arrangement matches the part physical pin arrangement. Nothing good comes of this.

Well, I assume you never debugged / verified a circuit then. In reality it greatly depends on the part whether it is feasible to draw the part like it is in the schematic. If you can, do draw the part as it is. When doing debugging / verification, all you need to know where to place a probe is the schematic and no need to count pins as you can tell by the external arrangement of the components which pin is which  in many cases. This saves a lot of time (which equals money).

Another good reason to draw a part in its physical form is that you have a good overview whether all pins have been assigned.

Actually, if the schematic looks like a mess when you draw a part in its physical form, the part is likely going to be a nightmare to get routed on the board anyway. So this is a good first sign of how difficult the board layout is going to be. Maybe a different part is more suitable.

Absolutely not! What on earth does "draw the part as it is" mean?!

The purpose of the schematic is to expose the design. That guides understanding what you should observe when you place a probe on a component.

Yes, the purpose of the schematic is to lead to something which is useful. And hence you grossly glossed over the 'it depends' part and the part based on very extensive hands-on experience that -if possible- drawing a part like it sits on a PCB is super immensly helpful to make a schematic actually useful. You seem to keep on wanting to create schematics like abstract art which at some point nobody understands. I for one don't want to be like Picasso in his abstract period; I want people to understand and use my schematics without needing any other documentation as much as possible. This all starts by very carefully choosing how to represent parts in a schematic. But also adding notes, expected voltages, etc. And for more complex circuits things like a block diagram, power-trees, power sequencing, power usages, currents, etc.

I could see a schematic symbol matching the physical component pins if it were a simple design. I'll confess, I rarely do this and I draw all my schematics from a circuit design oriented point of view. Input/Outputs flow right to left, High/Low voltage from high to low. An op-amp in an SOIC, MSOP, DIP, etc. looks like a triangle. If I really want to mess with people, the old trianglish symbol from back in the day.

Pins have their name and number on the schematic. Pins should have associated test points on the PCB. If there is a time that I truly need to measure a pin on a QFN package with a wettable flank, then I will have to pull out the datasheet. Besides, JEDEC standard for QFN packages is pin 1 is top left.

[nctnico]

I get that, but avoiding needing the datasheet gives you a massive boost in debugging speed and less clutter on your desk / screen. And no, you can't have test pins for everything. A PCB would become a total mess like that AND you can't really predict which test points you actually need for debugging / design verification as surprises may linger.

[16bitanalogue]

I get that, but avoiding needing the datasheet gives you a massive boost in debugging speed and less clutter on your desk / screen.

My standard practice is to always have the datasheet on hand; either a softcopy or a hardcopy. This is how I train engineers because it was beaten into me in the bygone days. I am not an expert on every product either, so it has always been a benefit to me to have the datasheet ready to go. Hell, I don't remember every single characteristic of the datasheets I authored myself.

[nctnico]

That method falls apart if you need to lookup the pinout of every multi-legged part on a board. Also, the purpose of a schematic is that you have an idea of what a signal should look like. In a good schematic even more so than in a datasheet! If a signal name is 'SPI_SCLK' you know you are looking for a clock on an SPI bus. There is no need to lookup the pin function. However, if only there is an easy way to identify which pin to poke... Hence the preference to draw parts as they are layout physically. Again, this is not possible for all parts but it is mighty handy when it is. Think of a simple linear voltage regulator for example. There is no real standard for the pin order on those things. When drawn as they are, measuring voltages on a board gets super easy without needing anything else than the schematic.

[Kim Christensen]

If you want to see well written manuals, take a look at the older HP ones written by boomers.

[tggzzz]

If you want to see well written manuals, take a look at the older HP ones written by boomers.

I'm not sure what "boomers" have to do with it. Competent engineers in a good company, yes.

Nctnico wouldn't approve, though. Those components don't look like what you see on a PCB. Presumably he would prefer (caution ascii art ahead!)

Code: [Select]

    ---------
  --| C B E |--   Q1
    ---------
        |

    ---------
  --|       |--   R1
    ---------
     
      --
     /  \
 ----\ +/----  C1 for a radial mount electrolytic
      --



Personally I get that information from a different type of diagram, like this...

[tggzzz]

I could see a schematic symbol matching the physical component pins if it were a simple design.

I can't[1].

Too often you see a schematic that looks like a solderless breadboard, with "please help my circuit doesn't work". You can't even tell if the intended design is correct, because who the hell knows which pin is the output/reset/discharge/etc on a 555! Just draw the effin schematic so that it vaguely resembles something seen in an application note.

No, I'm not going waste my life on the equivalent of dissasembling optimised object code back into C

[1] actually that is too strong with microwave circuits; e.g. consider a ratrace coupler

[Marco]

I don't understand what you mean by that, in that context.

The way industry handles opamps in schematics is convenient for absolutely no one.

Is inverting on top for inverting amplifiers only? Does the V+ go on top/bottom with non inverting input? Flip a coin for every bit of software, datasheet and schematic. Even in a single datasheet you will find the isolated symbol randomly flipped.

[tggzzz]

I don't understand what you mean by that, in that context.

The way industry handles opamps in schematics is convenient for absolutely no one.

Clearly it is convenient for most people, and following standard "design patterns" is A Good Thing in both hardware and software.

Is inverting on top for inverting amplifiers only? Does the V+ go on top/bottom with non inverting input?

Follow the standard design patterns seen in (decent) textbooks and application notes and schematics - unless you want to needlessly make it difficult for other people to understand the design.

Positive PSU voltages at the top, negative PSU voltages at the bottom, 0V in the middle.

For an inverting opamp circuit, the noninv input is connected to ground, and is therefore more neatly put below the inv input.

Flip a coin for every bit of software, datasheet and schematic. Even in a single datasheet you will find the isolated symbol randomly flipped.

No, you don't see that bad practice is everywhere.
Data sheets aren't circuits, and over time are containing less useful information. That's poor.
Just because you can see bad practice in some cases doesn't mean you have to lower your standards.

The OP is interested, sensibly, in good practice, not copying bad practices.

[Marco]

Positive PSU voltages at the top, negative PSU voltages at the bottom, 0V in the middle.

For an inverting opamp circuit, the noninv input is connected to ground, and is therefore more neatly put below the inv input.

For a non inverting opamp with a divider to ground it's the other way round ... but unless you have two separate symbols, or symbols without power, you have to compromise.

With a single symbol with power compromise which way? Flip a coin if you prioritize the neatness of the schematic or the orientation of the power, then flip a coin again based on your mood.

Also major software programs do disagree on which side V+/V- goes.

[tggzzz]

Positive PSU voltages at the top, negative PSU voltages at the bottom, 0V in the middle.

For an inverting opamp circuit, the noninv input is connected to ground, and is therefore more neatly put below the inv input.

For a non inverting opamp with a divider to ground it's the other way round ... but unless you have two separate symbols, or symbols without power, you have to compromise.

With a single symbol with power compromise which way? Flip a coin if you prioritize the neatness of the schematic or the orientation of the power, then flip a coin again based on your mood.

Also major software programs do disagree on which side V+/V- goes.

You are going to have to learn how to make your own symbols for components that aren't in a library. For something common and simple like an op amp, multiple symbols are usually available. If not, make your own symbol starting from an existing symbol. It isn't difficult, doesn't take long.

Having the traditional symbol demonstrates to other people that you take pride and care in your work, and that you understand the circuit's operation. But maybe that doesn't matter to you?

By "Major software programs", do you mean CAD program? No library - software, analogue hardware, digital hardware, RF, microwave, music, paper book, etc - is going to contain everything you might possibly need. Learn to use your tools.

[Marco]

The problem is not whether the symbols are present in the libraries of major software programs with schematic capture like say Eagle or Pspice, the problem is that there is only 1 symbol in each library AND they can't agree what to put on the top and bottom of the symbol (top and bottom being sides of course).

The software can't agree, designers can't agree and somehow I doubt even you add a new symbol every time the power connections and input connections aren't perfect for both neatness and consistency of power orientation.

PS. I think consistency of the inputs is generally more important than neatness, consistency has value of its own. Except for extreme cases like say three opamp instrumentation amplifiers. Otherwise, I'd rather everyone would pick a side and stick with it (and I'd prefer non inverting on top, but that seems a minority point of view).

[Kim Christensen]

I'm not sure what "boomers" have to do with it. Competent engineers in a good company, yes.

I was just pulling the OP's chain: 

I am about to go into battle with, as a term of endearment, Boomer executives who never had experience with day-to-day engineering tasks and will simply default to "Back in my day 30 years ago...so do it like we did."

It's a small company where the executives for the first time in decades are very close to the day-to-day; however, they try to enforce outdated methodology with documentation, process, and engineering methods that they used when they were individual contributors back when Marty was driving 88 MPH.

[tggzzz]

The problem is not whether the symbols are present in the libraries of major software programs with schematic capture like say Eagle or Pspice, the problem is that there is only 1 symbol in each library AND they can't agree what to put on the top and bottom of the symbol (top and bottom being sides of course).

The software can't agree, designers can't agree and somehow I doubt even you add a new symbol every time the power connections and input connections aren't perfect for both neatness and consistency of power orientation.

The software should NOT "agree" - because it is an electronic design issue. The software should enable whatever is best for the designer, both at the schematic and PCB level. I suppose you also complain that there isn't a single pad pattern for 0603 SMD components. There shouldn't be, since the optimal pattern is a function of component manufacturer and PCB production process.

The quality of libraries is (arguably) the key consideration when choosing any software/hardware language or CAD/RF tool etc. Ideally the library will already contain what you need, but inevitably they won't. In that case they should enable you to easily implement your own component.

I suggest you look at some different CAD tools and/or learn how to use all their capabilities.

PS. I think consistency of the inputs is generally more important than neatness, consistency has value of its own. Except for extreme cases like say three opamp instrumentation amplifiers. Otherwise, I'd rather everyone would pick a side and stick with it (and I'd prefer non inverting on top, but that seems a minority point of view).

No.

Easy fast comprehensibility is the most important attribute that a schematic should have. Consistency of representation corresponding to industry standard design patterns is key to that.

Example: you normally draw transistors in a different orientation depending on whether they are acting as CB/CB/CC/cascode/diff pair amplifiers, current mirrors etc. And that really really should not depend on whether the components pins are BCE, CBE, BECase, or anything else.

[tggzzz]

I'm not sure what "boomers" have to do with it. Competent engineers in a good company, yes.

I was just pulling the OP's chain: 

I am about to go into battle with, as a term of endearment, Boomer executives who never had experience with day-to-day engineering tasks and will simply default to "Back in my day 30 years ago...so do it like we did."

It's a small company where the executives for the first time in decades are very close to the day-to-day; however, they try to enforce outdated methodology with documentation, process, and engineering methods that they used when they were individual contributors back when Marty was driving 88 MPH.

OK 

(I did consider the possibility, but didn't want to presume that was the case. Honestly!)

[Marco]

No.

Easy fast comprehensibility is the most important attribute that a schematic should have. Consistency of representation corresponding to industry standard design patterns is key to that.

What consistency? Inverted power connections on schematics are incredibly common ... and I still doubt you actually make new symbols every time to avoid it.

My suggestion has the advantage in that it can actually be consistent, without needing two separate symbols.

[nctnico]

If you want to see well written manuals, take a look at the older HP ones written by boomers.

That template leaves a lot to be desired by today's standards. The part number for the transistor is missing for example. And with a much greater mix of components nowadays, I very much prefer to have complete part numbers (so you can enter the part number in Google and get the datasheet without needing to look at the BOM) and more information about the components. Like voltage rating & package size for SMD capacitors, tolerance & package size for resistors and current rating + DC resistance for inductors. All this information helps to give a good sense of what a circuit is supposed to do and also allows for a quick check on whether the voltage & current ratings are suitable.

[coppice]

That template leaves a lot to be desired. The part number for the transistor is missing for example.

If an HP schematic gives a part number its usually just an 8 digit HP code, so its not that meaningful to most viewers. Their manuals have a part code to part number table for every schematic, so its easy to find the part you might need to order, but the use of internal 8 digit codes for every part in their products means its not very helpful to have them on the schematics.

[nctnico]

That template leaves a lot to be desired. The part number for the transistor is missing for example.

If an HP schematic gives a part number its usually just an 8 digit HP code, so its not that meaningful to most viewers. Their manuals have a part code to part number table for every schematic, so its easy to find the part you might need to order, but the use of internal 8 digit codes for every part in their products means its not very helpful to have them on the schematics.

True, but for general use, it is highly recommended to have a meaningful partnumber next to the symbol. And with the way modern CAD packages work (especially decent ones which have the components defined through a database), it is much easier to update a part number is a schematic compared to the old days where updating the part number would mean modifying the circuit diagram or re-drawing it manually.

[TimFox]

That era of -hp- schematics used TH components, rather than SM.
It allowed editing of text-file BOMs when, for example, the resistor values were rationalized to use fewer discrete values, although it is helpful to have the resistance value on the schematic.
A full listing of parameters for a resistor would clog up the schematic drawing, but could be given on the BOM.
Note that the full part reference for the resistor adds the board reference:  A2R1 for R1.