DougGibbs, 15 August 2014 (created 15 August 2014)
I have a friend who does engineering consulting. A few weeks ago we met at the local Mexican place for lunch. He is a professional and charges professional rates for his work, over $100 an hour usually.
He said he charged four hours of work, for building a part needed on a schematic. Four hours!
It was basically a copy/paste exercise, except the data sheet was "secret". The vendor wanted to keep the part from falling into the hands of competition I guess. The PDF file was encrypted and required a password. When a PDF is encrypted, copy/paste does not work any more.
So, by hand he copied the pin out table for a 400 pin part. Sigh.
The thing is, he was not happy to bill the customer for this sort of make work project. That is not a high value activity for him or anyone.
For another example we should look at the Here are the Open Licensed BeagleBone and BeagleBoneBlack schematics as a PDF file.
The main processor is an AM3358 processor from Texas Instruments. The part is packaged in a XXX pin ball grid array (BGA) package.
Each of the pins had to be placed on a rectangle. There are too many pins to use one rectangle, so the part is split into multiple symbols, based on function. One huge symbol on page X is just for power pins.
A designer had to build that symbol. Check out the pin names " long pin name ". We can talk about that problem later.
To build a symbol, we change to the library editor, which for some reason is a different tool in every program I have ever used.
Now draw a rectangle and start adding pins. Edit the pins with the correct pin number. We can not forget, a different package means different pin numbers, so it has to be a different symbol. I guess some high end tools are smart enough to work around that, but none that I have used.
Each pin is then connected to a wire, and the wires labeled. For a bus, the wires are tied to a bus breakout, then to the bus line, which also gets a label.
The labels identify the connection. If a label is misspelled, or does not match, well, then the pins are not tied together in the net-list and on the board. Simple, right. Now repeat for every part not in the standard library.
Each wire that goes off the page gets an off page connector. In some packages this is needed, in others it is just the wire labels.
The off page labels sometimes have a cryptic list like, 9:A-3, 5:B-2. That is the page where the wire reappears, and the coordinates on the page. Remember the draftman's coordinate references in the page boarder and title blocks?
How much time was spent doing all that? How much of that time is wasted? My answer is a lot.
So, stop drawing boxes!
By now many of you are thinking, "Great, I found another crack pot on the internet:, or "What a fool, there is no way to replace schematics". A roll of the eyes and snort of derision and dismiss all this as random complaining. Yet another internet rant.
A schematic, that is the lingua franca of engineering.
There are some places a schematic makes sense. Analog circuits for one. The shape of the circuit matters and helps you identify an integrator from an amplifier. Sure, can't disagree.
But, for a mostly digital board with a processor and a lot of pins, the schematic is a bunch of rectangles and pages. How much value are we really getting from the drawing on paper model of circuit design?
I told the same friend I mentioned above, when we were working together at a start so many years ago I don't want to count, "You can't bitch about something unless you are willing to fix it."
I think we can do better. I am working on the solution and need your input to make a great product. Stay tuned to find out more.