Design Con 2015
Breaking News
Blog

Why I Prefer to Create My Own PCB Symbols

NO RATINGS
1 saves
Page 1 / 2 Next >
View Comments: Threaded | Newest First | Oldest First
MWagner_MA
User Rank
Manager
still waiting for good schematic symbols from chip vendors
MWagner_MA   6/3/2014 7:15:08 AM
NO RATINGS
I pretty much made the same transition through the years as far as schematic tools go.  No we don't have any written standards for schematics (yet), but we also find we need to make many of our own symbols.  I keep trying symbols offered by companies like TI, Microchip, Analog Devices, ect, but either they are not segmented logically (from my perspective) or they don't look good (text in weird places ect or overlapping lines).  When we create symbols, we try to share within our small design group (3 engineers).

antedeluvian
User Rank
Blogger
Altium has something
antedeluvian   6/3/2014 8:37:01 AM
NO RATINGS
I remember Intel used an off-sheet convention on its SBC (Multibus) schematics. Unfortunately, this no longer seems to be practiced, and I know of no current CAD system that provides this option.

Altium treats each sheet of a schematic as an individual sheet which must be added individually to a project. In my opinion this is an archaic approach since items of commonality like the title are not flowed through, bu must be added on each sheet. The interconnection is handled through an hierarchical inteconnection diagram which actually does define which sheet to access.

But for me it is no panacea. I still work with paper and so this is just another piece of paper and an added intermediate step. Nor does it indicate where on the sheet I should look for the net. I suppose we could institute a standard bringing all off-sheet nets to an edge.

Max The Magnificent
User Rank
Blogger
Ah, the Yom Kippur War
Max The Magnificent   6/3/2014 10:40:04 AM
NO RATINGS
I was 16 when the Yom Kippur War took place -- my best friend at that time was Jeremy Goodman who lived about six houses down the road / around the corner from us. Jeremy and I were the only two boys in our area (apart from Robert across the road who was a bit older than us and he was a slimy toady of no account) and we grew up together from when we were little kids (we're still in touch).

I remember when the War started and my mom sent me round with something she'd baked to give to Mr & Mrs Goodman, just to let them know we were thinking about them. And I remember how happy we all were when the war ended. I don't think I fully appreciated the magnitude of what was happening at the time.

antedeluvian
User Rank
Blogger
Re: Ah, the Yom Kippur War
antedeluvian   6/3/2014 10:42:50 AM
NO RATINGS
Max

 I don't think I fully appreciated the magnitude of what was happening at the time.

I was there and I don't think anyone knew how precarious the situation was for the first few days.

Duane Benson
User Rank
Blogger
Re: Ah, the Yom Kippur War
Duane Benson   6/3/2014 11:16:25 AM
NO RATINGS
AD – "I don't think anyone knew how precarious the situation was for the first few days"

At one point in my career, I worked with a former US Air force pilot whom had flown C-141 transports to Israel during that war. He described having to fly a very narrow corridor through the Mediterranean to avoid the airspace of the various countries that didn't want to get involved, or didn't want to let any help in. There was one area that was served by (then) Soviet air traffic control. He said it was quite uncomfortable to be relying on them, when flying in opposition to their allies, and while the possibility of nuclear war was being tossed about.

Duane Benson
User Rank
Blogger
Your own PCB symbols
Duane Benson   6/3/2014 11:31:48 AM
NO RATINGS
Here at Screaming Circuits, we see quite a large number of different board designs come through. One of the more common problems we see is having a footprint that doesn't quite match up with the actual part.

It's real easy to pick a symbol that's close, but ends up being a QFN form-factor when a QFP part will be used, or someone did a poor job or creating it and the rotation is off, or a few  pins are swapped. There are some diodes with different size pads. Some people will take a standard land pattern, assuming it's close enough. That can lead to the part moving, or uneven melting.

A lot of issues can show up due to footprint problems. If in doubt, I create a new footprint. Even if there's little doubt, it's best to do a thorough check before using the symbol/footprint.

dougwithau
User Rank
Manager
Paper models?
dougwithau   6/3/2014 11:39:21 AM
NO RATINGS
I've been wondering, now that most of us have a computer to work on, why do EE types cling to "sheets". The whole model of schematics is based on the number of pieces of paper. Some vendors sell based on "number of sheets" to differentiate between the lite and pro versions.

When building a micro processor symbol, it usually ends up being either one big box, or multiple boxes. One part smears accross 4-5 pages. 
Even worse, if you look at the symbols for the newer ARM processors, each pin can have 4-5 functions. The pin names are a paragraph all by themselves. "USBB2_ULPITLL_DAT2/USBB2_ULPIPHY_DAT2/SDMMC3_DAT2/GPIO_163/HSI2_ACFLAG/DISPC2_DATA18/USBB2_MM_TXSE0/SAFE_MODE" Yikes!

If there was a better desgin capture tool would you use it?

I've thought about making a web based attempt at something better, but would anyone change just based on "easier to use"? Is the schematic to ingrained in us old timers?

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/3/2014 11:49:39 AM
NO RATINGS
dougwithau

When building a micro processor symbol, it usually ends up being either one big box, or multiple boxes. One part smears accross 4-5 pages. 
Even worse, if you look at the symbols for the newer ARM processors, each pin can have 4-5 functions. The pin names are a paragraph all by themselves. "USBB2_ULPITLL_DAT2/USBB2_ULPIPHY_DAT2/SDMMC3_DAT2/GPIO_163/HSI2_ACFLAG/DISPC2_DATA18/USBB2_MM_TXSE0/SAFE_MODE" Yikes!

Wouldn't it be nice if you could (right?) click on the pin of the symbol and the select the chosen function from a drop down menu?

If there was a better desgin capture tool would you use it?

As long as it tied into the netlist format used in the layout. Or am I stating the obvious.

I've thought about making a web based attempt at something better, but would anyone change just based on "easier to use"? Is the schematic to ingrained in us old timers?

Part of me says that it makes sense to have one big schematic, but another part says that partioning is good for conceptualization. I also seem to have trouble moving around from end to end on a large schematic even now on a screen- it may be necessary to have the ability to have multiple views of the same design on different screens.

When I go to site and try to debug on a small laptop screen- I am not sure.

And as for resistance to change- you betcha!

dougwithau
User Rank
Manager
Re: Paper models?
dougwithau   6/3/2014 12:45:57 PM
NO RATINGS
We look at a lot of schematics from many of our customers. The only feature that matters is the PDF export. If the symbols and text can not be searched, I want to run screaming out of the room.

Even then it is only a text search, no context.

Netlist import and export or a standard is what really matters, I have that as the number one feature.

My thinking is there has to be a happy medium between drawing little boxes and ligning up wires, and the blinking cursor in a blank text editor when you start working with an HDL.

Max The Magnificent
User Rank
Blogger
Re: Paper models?
Max The Magnificent   6/3/2014 1:06:35 PM
NO RATINGS
@dougwithau: My thinking is there has to be a happy medium...

There is -- she's always telling jokes -- she has an office just around the corner from here LOL

betajet
User Rank
CEO
Re: Paper models?
betajet   6/3/2014 1:24:31 PM
NO RATINGS
Max wrote: There is [a happy medium] -- she's always telling jokes...

You should strike her some time :-)

[from the Old Jokes' Home]

DU00000001
User Rank
CEO
Re: Paper models?
DU00000001   6/3/2014 2:46:18 PM
NO RATINGS
"If the symbols and text can not be searched, I want to run screaming out of the room."


To be honest, Im rating non-searchable PDFs as one of 2 things:

a) Declaration of war (we once had a supplier delivering the
    schematics of an ECU (3 pages only readable if printed
    A3 or beyond) as a non-searchable PDF.
    This WAS the start of a war.

b) Demonstration of imbecility of the creator

betajet
User Rank
CEO
Re: Paper models?
betajet   6/3/2014 3:16:32 PM
NO RATINGS
doug wrote: I've been wondering, now that most of us have a computer to work on, why do EE types cling to "sheets".

It depends on what I'm doing.  If I'm probing a board, I like to have B-size schematics so that I can see "the big picture" all at once.  Otherwise it's like those AAA custom travel guides that show you each segment of the route on a separate page.  Some people like to navigate that way -- I like the "chart room" where Captain Nemo unrolls a chart to get the full picture of where one is and where one is going.  Scanning around a schematic on a computer screen is a PITA when it's already covered with terminals and debug consoles.

OTOH, if I'm considering a logic design inside a chip, I'm not going to be able to probe it so it makes more sense for each piece to be documented on separate pages.  But that's because a complex chip is more like a data book of smaller chips that are connected together at a higher level, with a block diagram that shows the big picture.

I once heard a great talk on map making.  A completely accurate map that shows everything is often useless.  Each map has to be created for a particular audience, and it's drawn to be most useful to that audience with some features drawn inaccurately so they don't confuse the important features.  They call this "cartographer's license".

betajet
User Rank
CEO
Re: Paper models?
betajet   6/3/2014 3:30:35 PM
NO RATINGS
doug also wrote: When building a micro processor symbol, it usually ends up being either one big box, or multiple boxes. One part smears accross 4-5 pages.

Whenever possible, I like to have schematic symbols of components with lots of pins to match the actual pinout, so that it's easy to correlate the schematic and the PCB.  This is quite doable up to a 208-pin PQFP on a B-size sheet.  It's harder with BGAs -- with those I'll put the power and ground pins in a separate block and if I'm feeling ambitious I'll make a rectagular symbol that matches the internal pad sequence, which you can get from the chip's BSDL file.

Regarding the alphabet soup of multi-use pins, there's nothing to stop you from taking a generic component for the part and editing the pin names to be just the setting(s) you actually use.  I do this with CPLDs and FPGAs, since names like "I/O32" are pretty useless.

Creating new symbols and customizing existing ones does take time up front, but will save lots of time in the long run when it's time to debug the design when the boards come back 6-12 weeks later.

JMO/YMMV

dougwithau
User Rank
Manager
Re: Paper models?
dougwithau   6/3/2014 3:39:34 PM
NO RATINGS
Betajet,

If I edit the pin names then one of two bad things just happened.

Either, the symbol in the library was just changed to my custom configuration. The information was lost, or must be recreated if that symbol is ever used again.

OR

The symbol was copied, then modified. Now I have done a bunch of work, for a one off symbol, and I have two almost but not quite duplicate parts in the library.

Again, I say Yuck!

Douglas.Butler
User Rank
Rookie
Re: Paper models?
Douglas.Butler   6/4/2014 7:23:35 PM
NO RATINGS
On complex parts like processors where each pin has multiple functions I always edit the pin names to create custom symbols showing the pin functions as I am using them in this instance.  If it means I have two diferent symbols for the same part used twice on the same board or sheet then so be it.  Some of my favorite chjips may have half a dozen symbols in my library for the different ways I use them.

mhrackin
User Rank
CEO
Re: Paper models?
mhrackin   6/4/2014 5:37:57 PM
NO RATINGS
As a high-level systems architect, I am a firm believer in the utility of CAD tools that include hierarchical capability.  Multi-level hierarchy would be even better.   That Page 1 is the top-level image of the entire product to me, and it would include all of the abstact blocks of the design, including COMPLETE definition of all interconnects, both internal and external.  Obviously, bidirectional update (forward and backward annotation) would keep things correct and synchronized throughout the design implementation phase.  Pages are just a convenient way to keep "score" of what's what and where.  My practice has been almost forever to name EVERY net using a standardized notation scheme.  That's especially important for e.g. analog, digital, power, and safety grounds!

Many of my designs had MANY pages, of such size and detail that "hard copies" were readable only on E or larger sheets!  However, "page 1" was always the definitive overview of the total system, and thus signal flows, etc. were very clear on one sheet.

dougwithau
User Rank
Manager
Re: Paper models?
dougwithau   6/4/2014 6:07:38 PM
NO RATINGS
@mhrackin

I am not arguing that you can not do a good schematic with existing tools. You can definately setup blocks that jump to the correct sheets, name every net, use directed off sheet connectors, and the correct map locators for every off sheet pin (A-5, or D-3, I always called them battship coordinates).

The tools don't seem to help with all that. Right click, properties, type in the net name. Same names are connected. Does the case matter?

I have seen notes tied to a circle for PCIe matched pairs. Is that something that comes through the netlist into the PCB package? From the Adobe PDF file, I dunno.

I am just searching for the better mousetrap.

mhrackin
User Rank
CEO
Re: Paper models?
mhrackin   6/4/2014 8:10:33 PM
NO RATINGS
@dougwithau:

 

Sorry I can't help with any recommendations.  I haven't touched any CAD SW for 5+years.  Last tools I used were old Mentor Graphics Boardstation suite AFAIR.  We had done a lot of customizing and adding scripts to take care of much of the "dogwork."

dadeus
User Rank
Manager
Re: Paper models?
dadeus   6/5/2014 8:16:30 AM
NO RATINGS
We use DxDesigner which allows sheet numbers to be entered as attributes.  This has the benefit that it can be updated automatically (should updates require insertion of new sheets) and that it can also be used with off sheet connector icons to add the reference link mentioned in the article.  Although it won't add the alphanumeric block reference, it will add the sheet number(s).  It also allows large fpga parts to be split among banks so we can break the symbols down to whatever size lends itself to better schematics. 

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/5/2014 9:21:19 AM
NO RATINGS
Daedus

We use DxDesigner which allows sheet numbers to be entered as attributes.  This has the benefit that it can be updated automatically (should updates require insertion of new sheets)

PCAD had this, but Altium (the "upgrade" path) does not.

and that it can also be used with off sheet connector icons to add the reference link mentioned in the article.  Although it won't add the alphanumeric block reference, it will add the sheet number(s).  It also allows large fpga parts to be split among banks so we can break the symbols down to whatever size lends itself to better schematics.


Now this is nice. I took a quick look at DX Designer which now appears to be part of Mentor Graphics. I can find no mention of cost or download, although I am often flumoxxed by web screens. I did find a free download on Google, but there is little documenation if this is legal.

 

GSKrasle
User Rank
CEO
Re: Paper models?
GSKrasle   6/5/2014 2:29:47 PM
NO RATINGS
I'm old enough to remember tape and film, big photoreducers, diazo machines and the like. I cut my teeth on early versions of PCAD and PADS, and saw many examples of very very bad use of tools. I have strong opinions, some that people will disagree with, but if you think about it, the Library is the most critical part of the CAD system. It behooves us to make sure that all library parts are _perfect_ and that conventions are clear, consistent, and enforced. A "Librarian" with approval/editorial authority (or complete authority) is one way to do this.

Altium has a serious weakness in its "free-form" component attribute system: I have accumulated component definitions from several sources; fields "MFRPN," "MfrPN," "Mfr_PN," "Mfr#," etc., and "W," "Rating," "Power," "Altitude" (?????!), and many others appear. It's a mess, and would not have been if a canonical set of basic attributes had been defined from the outset.

One set of conventions will probably never be appropriate for all users, but there is one choice that divides the world: Are resistors defined with a manufacturer's/supplier's/stock part number for each value+rating, or are they simply put-down on the design and then their values defined, so that "jelly-bean" parts might be ordered? Highly-regulated industries are forced into the former convention, but low-cost products are served by the latter. In the former case, choice of already-defined parts is often economically advantageous, in the latter, less-so.

Anyway, hearkening back to the PADS paradigm (excepting some of the as-supplied conventions), here are some things, great and small, that I like and dislike:

1:

Most parts should be defined to have at least two "gates." For Logic, this can be one "Power Block" for supplies and others for logic functions, which might be of several types: a control block and several individual channels (think 74245). For a transformer, each winding is a gate, and for resistor networks (remember those?), a "Common Terminal" gate with one pin, and several one-pin "Resistors." 'Same for connectors. This convention allows for the power sections and bypass capacitors to be gathered appropriately (as mentioned below), and allows flipping/mirroring to optimize the "flow" of the schematic. Normally/often the individual "gates" of the design will be shown contiguously, like a single symbol, but they don't HAVE to be.

Defining "hidden" power pins assigned to nodes "3P3V" and "Gnd" or any hidden pins at all, is wrongheaded. Parts defined as monolithic blocks, so wires have to swirl and cross, or you are forced into just labeling pins with textual node names are lazy-now, painful-later.

2:

Sloppy flow is bad work. The only place I have found for not orthogonal wires on a schematic is S-R flip-flops (exception for late-breaking mods). L => R, T => B, if you please!

3:

Cross-References! Make Off-Page symbols with "pointed edges" to show signal-flow, and node-names, and a list of sheets and coordinates of connected off-page symbols. And please please be careful or prohibit "off pages" that go elsewhere on the same sheet, as that invites missing them and ensuing confusion. Wires are much more understandable than textual references! Also show the node-names in several places next to the wires, for understandability. "Schematics" where many/most/all connexions are made through node-names are not even as good as lists!

4:

Meaningful part symbols:

I like a basic representation of the internal function (rather than a blank rectangle) to facilitate understanding and debug. Keep 91-1984/60617-12 away from me: if I only have a daisy-wheel or Selectric, I don't need to print it. Symbols are like letters. They should be as large as necessary, but not larger.

If it can be determined, make a distinction between "Not Internally Connected" ("NIC") and "Make No Connexion" ("MNC"). (MNC pins may include ones reserved for future functions.) It is often useful to ground genuine NICs to facilitate "blue-wires" and logic-analyzer, emulator, etc. grounding, and even heat-sinking.

It's also nice to have alternate (DeMorgan) symbols.

5:

"Redundant" information:

I like a sketch of the internal connectivity of a sensor or such: placed by the connector on the schematic, this is valuable in understanding the circuit's operation.

Likewise, I like to put package pinouts ("ebc") by the symbols to facilitate debug. I have been known to steal the pictures off D-K's site, label them (MfrPN, Pin1, etc.) and paste them.

Text notes wherever the operation is not obvious. Basic design equations.

I like to put some non-PCB parts on the schematic, even if they are just in the forms of stars or dots, to indicate heat-sinks, default jumper locations, etc.

Some regulatory schemes apparently prohibit the inclusion of non-essential information like these on schematics, and some "gatekeepers" enforce this rule, like pedantic grammar-school English instructors. I hate having to have the schematic, BOM and Datasheets all on my desk at the same time: it's too crowded. The documentation should include what you need to do your work, within reason, even if you have to use the label "Indication Only" a lot.

6:

Reference Designators can carry more useful information than simply uniqueness. "Rn" vs. "Cn" is an example. The order in which components were placed on the schematic is of course very interesting, but not very useful. Useful things can include numbering components in patterns when a functional block is repeated, having the numbering range reflect the functional block, or even having them reflect the coordinates of the component on the PCB. Why are so many people worried about gaps in the numerical list?

elizabethsimon
User Rank
CEO
Re: Paper models?
elizabethsimon   6/5/2014 4:45:22 PM
NO RATINGS
Excellent summary of rules. I pretty much agree with everything.I especially agree with your comment about "hidden" power pins. When i was using PADS, I re-did many of their standard symbols that had hidden power connections. It wasn't until later that I fully embraced the separate power block concept.

The company tht i work for has a PCB group that does the clean up on the schematic before starting on the PCB layout. they enforce most of the rules you mention. We do allow both off-page and on-page connections. The off-page symbols indicate direction and are labeled according to sheet location. The on-page symbols are different so they can be distinguished. Also, we usually only use on-page symbols to avoid having a lot of wires run from one side of the page to the other.

Another thing that I learned at my current job is the benifit of labeling resistors with "value, power, tolerance" and capacitors with "value, voltage, tolerance"

 

zeeglen
User Rank
Blogger
Re: Paper models?
zeeglen   6/5/2014 5:04:18 PM
NO RATINGS
@elizabeth I especially agree with your comment about "hidden" power pins.

Ditto.  The librarian can hook up hidden power pins wrong such as in http://www.eetimes.com/author.asp?section_id=30&doc_id=1284662 .  When power and ground pins are accessible one can place a few ohms between each device and power plane to reduce digital noise, and force each power pin to have its own decoupling capacitor.

I had one library component that showed two diodes in a 3-pin package.  The specs in the corporate data base looked good so I used it.  When I got the prototype boards back I discovered that the part was actually a single diode with 2 pins connected together!  Then when I got the symbol corrected, everybody else that used only one diode of that same component had it disappear from their schematics.

GSKrasle
User Rank
CEO
Re: Paper models?
GSKrasle   6/5/2014 5:52:25 PM
NO RATINGS
Oh, and can we PLEASE settle on a way to indicate active low signals? The gods of word-processing give us underline, strikethrough and double strikethrough, bold, italic, super and sub, but why not overbar? It seems like the attribute set is optimized for lawyers only.

\signal\

/signal

*signal

signal_N

....

   

zeeglen
User Rank
Blogger
Re: Paper models?
zeeglen   6/6/2014 1:21:08 PM
NO RATINGS
@GSKrasle a way to indicate active low signals?

Good question.  A few more:

~signal

signal~

-signal-

signal#

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/6/2014 1:32:20 PM
NO RATINGS
GSKrasle

 

but why not overbar?

At least both PCAD and Altium have that. In Altium though you have to do it for each letter in the line and not once for the whole line.

I seem to remember it was possible in Autocad, but I reaslly doubt anyone is doing schematics in that anymore.

 

GSKrasle
User Rank
CEO
Re: Paper models?
GSKrasle   6/6/2014 2:39:54 PM
NO RATINGS
Overbar?

It's possible letter-by-letter in [one common word-processor] using proprietary character-combining commands, but is awkward and nonportable. It can be done in equation editors too, but again, nonportable.  "Combining Overline" in Unicode is supposed to work, but this is what appears here when I try it: 1.

http://www.fileformat.info/info/unicode/char/0305/index.htm

http://wordfaqs.mvps.org/overbar.htm\

If you can get seven-segment fonts, then why not an overbar font?

Can Altium load fonts?

(A seven-segment font source: http://www.twyman.org.uk/Fonts/)

(Seven-segment fonts are useful for writing instruction manuals when a controller with such a display is being discussed: Instead of saying '"Press the button until the display says "start seq,"' you can show what the display would actually look like. I originally used a drawing and manually turned segments on.)



 

 

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/6/2014 2:47:52 PM
NO RATINGS
GSKrasle

If you can get seven-segment fonts, then why not an overbar font?

Good Point! That is more of a windows thing, so surely some thrird party can do that- any volunteers?

Can Altium load fonts?

Yes it can, but I would be wary of it. If you change the fonts on a symbol and then do a Force Update, it reverts to the default font. Apparently an acknowledged bug!

 

GSKrasle
User Rank
CEO
Re: Paper models?
GSKrasle   6/6/2014 3:32:10 PM
NO RATINGS
Overbar?

I don't trust Altium's font-handling, as it apparently can't ROTATE text.

I'm OK with using bitmaps in component decals, so there's no actual text, but pin names and node names would be facilitated if an overbar attribute or font were available: that would preserve serarchability.

Incidentally, here is an example of a snipped (stolen), annotated, and re-snipped bitmap of a kind I find helpful, but the MfrPN is obviously not searchable:



As long as a wishlist was implicitly mentioned, let me second the suggestion that on parts like µCs, displayed pin names (and open-drain, totem-pole, input, etc. attributes) should be available in a drop-down! And I wish that every time someone makes a four-way schematic connexion, they were forced to rework twenty PCBs. 



 

 

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/6/2014 3:48:52 PM
NO RATINGS
GSKrasle

I don't trust Altium's font-handling, as it apparently can't ROTATE text.

Well that isn't really true in its strictest and very narrow sense. You can see in the left hand (power block) of my Figure 1 where the text is rotated by 90 degrees, but it is severely crippled- if you rotate it another 90 degrees it flips back to 0 degrees and 270 reverts to 90. Another example: compare pin 3 in Figure 2(in PCAD) and Figure 3 (in Altium). There is no way to get the PCAD orientation in Altium for either the pin name or the pin number.

xjordanx_#1
User Rank
Rookie
Re: Paper models?
xjordanx_#1   6/9/2014 9:45:56 PM
NO RATINGS
There is no way to get the PCAD orientation in Altium for either the pin name or the pin number.


Actually this is also not a true statement. Pin and component text can easily be controlled to suit personal taste.

zeeglen
User Rank
Blogger
Re: Paper models?
zeeglen   6/6/2014 2:49:33 PM
NO RATINGS
@antedeluvian, GSKrasle   In Altium though you have to do it for each letter in the line and not once for the whole line.

Same with TinyCAD, each character must be preceded by a reverse apostrophe.  If doing a text find later the characters must be entered into the search field exactly the same way.


Nickel65
User Rank
Rookie
Re: Paper models?
Nickel65   6/8/2014 10:33:29 PM
NO RATINGS
At least both PCAD and Altium have that. In Altium though you have to do it for each letter in the line and not once for the whole line.


You don't have to do it for each letter. Under Preferences | Schematic | Graphical Editing, there is an option called "Single '\' Negation", select this and voila you only have to place the '\' at the beginning of the net text.

 

antedeluvian
User Rank
Blogger
Re: Paper models?
antedeluvian   6/9/2014 8:47:50 AM
NO RATINGS
Nickel65

Under Preferences | Schematic | Graphical Editing, there is an option called "Single '\' Negation", select this and voila you only have to place the '\' at the beginning of the net text.

Thanks for this. I wonder what else I am missing, hidden amongst all the options.

 

xjordanx_#1
User Rank
Rookie
Re: Paper models?
xjordanx_#1   6/9/2014 9:39:15 PM
NO RATINGS
Altium has a serious weakness in its "free-form" component attribute system: I have accumulated component definitions from several sources; fields "MFRPN," "MfrPN," "Mfr_PN," "Mfr#," etc., and "W," "Rating," "Power," "Altitude" (?????!), and many others appear. It's a mess, and would not have been if a canonical set of basic attributes had been defined from the outset.

 

I like this comment. There were older versions of Altium's software (like Protel 98) which had much more rigid parameter field names. However this imposed harsh limitations on what could be done with components. Overall, it's better to have the flexibility, but that also means someone (ie. a librarian) has to take responsibility for naming convenstions and parameter management. 

Luckily the list based tools for parameter management, or if using the Vault, the CMPLIB editor make this a spreadsheet style approach so it's hard to mix things up.

The problem does remain when you bring in different libraries from different places where no-one has adhered to a standard nomenclature. It would probably benefit all of us if we were to work with JEDEC or IPC to formalize a naming convention for parts and parameters which designers could choose to adhere to. (Then we can ask the semiconductor vendors to use it!)

xjordanx_#1
User Rank
Rookie
Re: Paper models?
xjordanx_#1   6/9/2014 9:30:26 PM
NO RATINGS
PCAD had this, but Altium (the "upgrade" path) does not.

Acutally it does. Everything is parameterized and the idea is to use templates, which are or can be updated through a batch process. 

In fact, the sheet numbering can reflect hierarchy with dot separators - why not make a call to tech support to find out how to do it?

Rick.Smith_#4
User Rank
Rookie
Re: Paper models?
Rick.Smith_#4   6/4/2014 6:37:20 PM
NO RATINGS
Sheets still have validity.  Especially if you work for a company that is "paper based."  I work for a medical company where our documentation control system is paper based (the only official copy per FDA rules is the one stored by document cotrol and the official copies are copied from that original and stamped "copy").

My microcontroller board schematic has 41 pages.  The first is the revision and other information.  The second page is the high level hierarchical "function" blocks and interconnections with the page numbers included in each block for that circuit block to act as a road map to get to a particular area of the circuit for troubleshooting.

I really could not imagine having it on one "sheet" or mini blocks with only net names sticking out with no real indication of circuit flow.

 

tb100
User Rank
CEO
why create a schematic
tb100   6/3/2014 2:23:11 PM
One of my pet peeves is when engineers draw their schematics by putting parts on the sheet then rely on net names to create the connections. Hey, it is easier to draw than lining things up and putting in all those annoying nets, and as long as it connects things up to create a correct netlist then you are doing it right. Right? 

No. If you do that you might as well just avoid the schematic altogether and just create the nelist from scratch. (In fact there are vendors that have products that will create a netlist from a spreadsheet, which actually works really well for things like backplanes).

But a schematic has another purpose besides creating a netlist for layout: it is documentation.. Therefore, it should show connectivity and function. Ideally it should almost look like a block diagram.

I draw my own symbols so that processor memory interfaces line up to DIMM interfaces so the nets flow straight across. I modularlize, so functions are grouped together.

Layout engineers, board fabrication and assembly engineers, and debug technicians will all use your schematic. Will they be able to figure out how the circuit works from the schematic, how signals flow? Is the schematic kept up-to-date? In other words are the parts shown on the schematic the actual ones on the finished board? 

A well drawn schematic makes the entire process of building and testing the board go well. A poorly drawn schematic will slow things down in ways you might not even realize.

Navelpluis
User Rank
CEO
Re: why create a schematic
Navelpluis   6/3/2014 4:12:00 PM
@ tb100

Hear say hear say !! 

I agree more with you than my brains can cope ;-)

Seems that I am old-school, just want to make great schematics for the whole process to be easier, and that counts even for myself. Part of the crativity process for me is to forget things within 3 months.... (or call it limitation in intelligence ;-) Good schematics help a lot.

My career after polytechnical school started with PCAD under DOS as well. The same route, except for the Altium part. Here I was lost, I just could not work with it. And now under Chinese government, trying to get your designs "into *their* cloud" makes me shivver, no way we are ever going that route. 

So I am still using PCAD 2006, bought Cadence, but did not find the time to go and use it properly. Cadence tells me to do the whole route again, all symbols and shapes pass my hand.

Lots of people have no clue what this does for an engineer, switching between CAD products. OK, if you do it the whole day it certainly will be easier, but CAD is only 30% of my time, the rest is hard core engineering.

So cheers for the writer of this article. Let me advise to the CAD companies to read this article carefully: I said this many times before: Don't be just a money maker, but enable people to make wonderful things with your software. Look at old stuff like PCAD and add the new high speed stuff to it, that's what I basically think...

 

krisi
User Rank
CEO
Re: why create a schematic
krisi   6/10/2014 12:32:09 PM
NO RATINGS
I agree @tb100...it is my pet peeve too...I hate connections by nets...make it graphically clear what you are doing!

dougwithau
User Rank
Manager
Schematic sharing
dougwithau   6/3/2014 3:44:14 PM
NO RATINGS
This is a fun debate, keep up the arguments. 

How many people do you share the schematic with?

The tools all make entering and building a schematic a one person job. They come from the days when sharing just did not make sense.

There are some online efforts, but they seem to be recreating the paper model of sheets and symbols.

The schematic needs to go to the board designers, the fab house (yes it should, not just a net list), technicians, the purchasing and parts procurement people, contractors, and vendors. I have been all of those people, sometimes all at once. Is emailing around a PDF file the best we can do?

Do you have concerns about sharing or doing a schematic online?

Roba66
User Rank
Rookie
Altium and Other GUIs
Roba66   6/4/2014 5:53:53 PM
NO RATINGS
I use Altium and I agree it is a pain to manage symbols and libraries. The most productive schematic symbol library tool I had was early Orcad where the library was a text file and a new part could be added in seconds. Now we seem to have to use GUIs for everything, which is not productive from my user perspective. (a GUI cannot be automated for one thing)

In Circuitmaker the footprints were a lot easier to manage because there was a fairly complete footprint library which could be matched up with components. Altium seems to provide a lot of libraries and I spend a lot of time searching for things, then give up and design my own footprints. When I do find footprints from different vendors they often have different VIA sizes to complicate the drill files, so I have to change those. 

One further gripe about Altium, the layer controls for PADs in components is very awkward and time consuming, the component GUI works differently than the layout GUI.

I generate a lot of Gerber level patterns, typically a couple layers of antennas and such, that is another reason I would like a textual interface, there is no way I could generate such patterns in the component GUI it would take years.

 

traneus
User Rank
Rookie
text-file part libraries
traneus   6/8/2014 11:39:21 PM
NO RATINGS
I use gschem for schematics, in part because the libraries are ASCII text files (also, gschem is GPLed). I fondly remember enjoying the old DOS386 OrCAD text libraries Roba66 referred to. I find it much easier to edit a text file to be exactly what I need, than to struggle with a GUI editor.

For digital designs, I go directly to a commented netlist text file and skip the schematic entirely, for all the reasons mentioned in previous posts. The netlist format must allow comments that will be ignored by netlist-reading programs. If necessary, I can write my own comment-stripper program to remove lines starting with #.

My experience writing and maintaining embedded software and VHDL code, has taught me that text representations scale much better than do graphical representations. One good comromise, is top-level graphical representation, and text representations below.

For designing boards, I use PCB, again for text-file libraries and for GPL. A few years ago, I designed some boards full of spiral coils, one connector, and no other parts. For these boards, I wrote C programs to directly create the needed Gerber artwork from numerical tables in C arrays. The disadvantage was that I did not create fabrication drawings.

markkk
User Rank
Rookie
I find CAD package symbol libraries aren't very helpful
markkk   6/6/2014 12:18:16 PM
NO RATINGS
I almost always draw my own symbols which replicate the physical layout of the chip(s) involved.  Usually a PIC in my case plus whatever else is required around it.  This means that as I'm doing the schematic I'm planning the PCB layout at the same time.

MeasurementBlues
User Rank
Blogger
Schematic symbols: Don't get me started
MeasurementBlues   6/10/2014 1:31:09 PM
NO RATINGS
Schematic symbols: Don't get me started. Too late.

I was EDN Design Ideas editor from 2008 to 2011. Longest three years of my life. EDN was still in print at the time and we had standard circuit symbols. But, schematic software often used different symbols for the same thing, Even for ground and I'm not talking just analog or digital. This was the standard symbol for ground.



But, some schematics came in with jusr one short bar perpendicular to the long line, but others used a angled single bar. When I started, one contributor, whioc sent in schematics almost weekly and was often published, drew all schematics by hand and scanned them. We had to redraw everything to get a consistent style for print. We had art person who redrew the schematics and she understood the any of those symbols meant the same thing. I didn't have to explain. Life was easy, relatively speaking.

When EDN was sold in early 2010, the new owner (not UBM) didn't bring her alsong figuring the existing art department could take over. Wrong! they coudln;t handle schematics. Much to detailed compared to what they were used to. I had to redraw everything so the art people could redraw again. They still often got things wrong.

At this point, a created a PowerPoint file and pasted in symbols. The symbol library also went to the person who was hand drawing schematics. After that he sent me beautiful schematics in powerpoint.

Today, EDN just posts the author'soriginal schematic, sometimes with alittle editing. Michael Dunn has it easy.

Of course, previous DI editors who did the job pre-email remember having to send corrections back to authors through postal mail. So relatively speaking, I had it easy.

MeasurementBlues
User Rank
Blogger
See Nice Circuit, Ugly Schematic
MeasurementBlues   6/10/2014 1:33:37 PM
NO RATINGS
Antedeluvian,

See


MeasurementBlues
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
MeasurementBlues   6/10/2014 1:35:37 PM
NO RATINGS
antedeluvian
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
antedeluvian   6/10/2014 1:46:14 PM
NO RATINGS
Martin

And this one

Why I Hate Your Schematic Diagrams

What can I say? Jon is a hero of mine.

I must say I have the same problem in house.Often our guys will use our in-house part number for a component which is meaningless when you are trying to follow the circuit. CD4013 is just so much more helpful that IC01MC14103BC-PB (not a partcularily bad example, but you get my drift). 

zeeglen
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
zeeglen   6/10/2014 3:19:25 PM
NO RATINGS
@ antedeluvian Often our guys will use our in-house part number

Back in the bad old days we could not even place a resistor onto the schematic until it had been given a corporate part number and was entered into the CAD library, which caused delays of several days.  To plant it on the schematic one had to type in the corporate part number.  No such thing as a generic resistor. A fast work-around was to plant them all as 1K resistors then ECO the BOM later.  This did not endear engineering to the documentation control people.

MeasurementBlues
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
MeasurementBlues   6/10/2014 9:23:49 PM
NO RATINGS
@zeeglen

I had that issue at GCA (long out ofbusiness bu that's another story). But previous engineers had put obsolete singe-sourced parts on the BOM and purchasing needed to provide parts for a build. Sometimes there was an acceptable substitite but often not. Redesign time. Kept us engineers in business.

MeasurementBlues
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
MeasurementBlues   6/10/2014 9:27:56 PM
NO RATINGS
When I was at GCA, the company spent something like $100k for aCAD system from Valid Logic Systems. I was the first to use it. Some of the symbols didn;t meet company standard but I used them anyway. I'd come back from the CAD room with C-size schematics. The drafting people hated it because they saw their jobs on the line.

antedeluvian
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
antedeluvian   6/10/2014 1:38:41 PM
NO RATINGS
Martin

Thanks for the pointer.

See

 

 

I agree with everything he says, and he says it so well.

MeasurementBlues
User Rank
Blogger
Re: See Nice Circuit, Ugly Schematic
MeasurementBlues   6/10/2014 1:38:44 PM
NO RATINGS
Here's a lovely little schematic from 1992.

 

Thinking_J
User Rank
Rookie
Agreed!
Thinking_J   6/11/2014 8:38:34 PM
NO RATINGS
I have similar (nearly same) issues and concerns about what a schematic should be.

Your statement "I remember Intel used an off-sheet convention on its SBC (Multibus) schematics. Unfortunately, this no longer seems to be practiced, and I know of no current CAD system that provides this option."

I have used most of the systems out there .. currently I am using CADint. It can automatically extract the page(s) where a connection or bus port goes and note it on the schematic at each port . So, if a signal goes to pages 4,12,23 - it will noted on each signal port involved. It would get messy if it tried to document the x-y location for each connection port... on all the other connection ports (single or bus)

Other simple items that used to be taught to engineers:

- no crossing connections! (a missing or hard to see "connection dot" can completely confuse things). All wire connections should be with a "TEE" connection. This is similar to avoiding the use of certain letters for revision control (capital I or O being confused with lower case L or zero).


- as noted by others, If the design is more than 1 page - make the first page a Block diagram, explaining things. I don't see the need (on CADint anyway) to document the actual signals between pages on the block diagram. A simple indication of existance of signals between appropriate pages / sections is generally "good enough". I love "smart" busing. (bit "0" on address bus not confused with bit "0" on data bus)..no need for A0 and D0 to keep them apart.

- Schematics should be able to be read without the CAD system or the need for text searches in PDFs. (first part  of comment - please identify every location the signal goes to)
 Basically, there are still users of the schematics that will be using hard copies (paper).... be nice to these people, make it usable for them, and the end product will be easier for everyone to read.

 

I won't put up with a CAD system that doesn't give me control of the location (at any resolution I want), font , size of the text on each component. Mirroring a schematic shape shouldn't mirror the text. But not all of us have the option of chosing the system they are using.

No matter how large the library is... I too, end up creating or re-creating most of the schematic symbols. I am just too picky.

I don't see this changing for awhile.

 

 

Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week