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Why I Prefer to Create My Own PCB Symbols

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MWagner_MA
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still waiting for good schematic symbols from chip vendors
MWagner_MA   6/3/2014 7:15:08 AM
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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
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Altium has something
antedeluvian   6/3/2014 8:37:01 AM
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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
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Ah, the Yom Kippur War
Max The Magnificent   6/3/2014 10:40:04 AM
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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
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Re: Ah, the Yom Kippur War
antedeluvian   6/3/2014 10:42:50 AM
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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
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Re: Ah, the Yom Kippur War
Duane Benson   6/3/2014 11:16:25 AM
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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
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Your own PCB symbols
Duane Benson   6/3/2014 11:31:48 AM
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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
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Paper models?
dougwithau   6/3/2014 11:39:21 AM
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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
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Re: Paper models?
antedeluvian   6/3/2014 11:49:39 AM
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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
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Re: Paper models?
dougwithau   6/3/2014 12:45:57 PM
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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
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Re: Paper models?
Max The Magnificent   6/3/2014 1:06:35 PM
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@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

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