4-20mA Precision Source Ideas

The OLD DAYS used a "loop-over" line crossing.

The NEW, fine resolution stuff is WHY we ALL now do not use the loop-over, and ALSO why a line cross is NOT a node EVER, and IF a node is needed, then the line gets split and TWO nodes get laid out.

THAT *IS* the convention, John. Whether you want to accept it or not, you denying it makes you the uneducated chump.

I just did a simple audio mixer/hybrid thing that has 1100 parts. The schematic fit on five pages (with four instances of one and twelve instances of another ;-).

Our base unit has about 1400 parts on one board and another 400 on another. They were going to put a block diagram on the cover but no one could draw one that was worth the expense to screen it on.

DimBulb working at his job:

I used to put cutting data into a VAX for a set of three plasma cutters, (around 1990) all cutting stainless, for institutional (hospital) and government fully welded HVAC ductwork.

It would 'nest' all the pieces we entered such that the minimum scrap was generated. Plasma moves a bit faster than flame, and the stock is a lot thinner, of course.

The robot had to be calibrated for flame tool speed, and the cutting probably had to be real time monitored by someone with a kill switch because torches sometime stop cutting and simply flare wide. Then you have to stop, and reset the flame-bot, AND the drawing follower. If it was thin stock, you could use plasma, and be sure that it was cutting the entire path. Can't do that with hull plate though. Sheet stock, yes. Plate stock can be done, but the plasma head would be huge, and gas is cheaper at that point.

Avondale Shipyard was a pioneer of this sort of automation. They also used IBM mainframes to figure the best way to make a curved ship's hull out of cut-up and welded flat plates. The tricky part was the underwater bulbous bow, which seriously reduced drag and fuel consumption, but was tricky to fabricate.

This (early-mid 70's) was before stuff like SolidWorks was available, so they didn't do truly accurate 3D designs of stuff like piping. They just showed about where the pipes should run and let the shipfitters deal with the real-life issues, like pipes colliding with other pipes.

On one ship they sold, about a year after the ship was put into service, the crew was trying to trace a pipe and saw it go through one bulkhead and emerge from another about 50 feet away. There was a dead space. They cut through a wall and found a fully equipped machine shop with no doors, but with the lights on.

I designed throttle and boiler controls, fog gongs, bell loggers, flame detectors, marine stuff like that. The first closed-loop control system I ever designed was a 32,000 steam turbine. Scary stuff for a kid. I made some mistakes but didn't quite kill anybody or disappear the town of Benecia.

John

Who and their army are going to stop me?

John

Is that a hierarchial schematic? I don't do that!

We're increasingly trying to reduce parts count, by using r-packs, packaged switchers, stuff like that. 1100 is too many parts for one board.

I saw one board, part of an Anritsu memory tester, that had over 3000 bypass caps!

Except for simple stuff, sheet 1 of all my schematics is a block diagram and table of contents.

ftp://jjlarkin.lmi.net/V350_sh1.pdf

John

have

Absolutely. Hierarchical is the only way to fly for repetitive circuits. Makes the top-level schematic a block diagram, too.

You write flat VHDL? Same difference.

So you want to make more boards? This product is one board (plus a steel case and brick).

I've seen some pretty ridiculous circuits, too.

I'm starting to do that but the graphic tools suck. Anything with a picture makes the schematic too big.

Too much redundant information.

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VHDL doesn't have a BOM, or silkscreened reference designators!

PADS isn't bad as a drawing tool, for simple stuff like this. The graphics takes very little room in the file... it's just lines and text.

The table of contents is great. Saves a lot of flipping through pages. Just starting with the TOC is a great organizer.

And the block diagram gives the big picture at a glance. All that is handy when you need to revisit a circuit five years after you forgot all about it.

When I design something, first I write the manual. Then the schematic TOC. Then the circuits.

John

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No problems. In the above example, the last two digits of each component are the same for each instance (modulo 50 in the case of the circuit with 12 instances). The reference designators work out very well. OrCAD could make this easier, but it's not too bad. The BOM works out perfectly. No issues with the silk, though 0402s make things a bit tight in areas. All components do have their ref-des silkscreened. Hell, even the dongle I just finished up (108-up on a ~7"x7" board) had all the reference designators (readable) in the silk.

The only problem we're having with silkscreen is getting the &^#@ fabs to keep the ink off the pads. We just shipped another few hundred boards back this week.

OrCAD can draw boxes and lines but it's *really* crude. It's almost impossible to get text to line up with the stick figures (it wants to walk around depending on the magnification). I was referring to embedding bitmaps. I've done it but the others hate it when I do it. It makes working in the schematic even slower. I'd like to put some key waveforms in the schematics for the service techs. There isn't a good way now.

Sweep the redundancy up a level of hierarchy. ;-)

But it doesn't work if it's too busy.

Good plan. We work bottom-up because they never tell us what they want until the product is complete (and then we didn't make what they wanted, obviously).

"Probably"? You don't know? This is another piece of dreamed-up pile of crap by AlwaysWrong.

I wonder how he would represent the "star ground" etc?

People who don't draw circuits, or limit themselves to a 555 and a few parts, don't often have four things to connect together.

John

This is how I annotate schematics of my IC designs before I send to my layout guy...

I'd suggest that if you're an engineer who's running a company -- as John is --, and assuming you understand the rationale behind some particular convention -- as I believe John does --, it's absolutely standard to decide that that convention doesn't really apply in your case and to do things differently.

You probably don't like John putting a dot on his Schottky diodes either!

I say... let the man run his company the way he sees fit. That company is successful, providing jobs for a bunch of people, with no sign that his not drawing schematics or washing boards the way you do is going to negatively impact his sales. It's hard to argue with success...

---Joel

Back in the '80s I had hoped that some TV manufacturers would start pasting a CD ROM disc inside the rear cover, but no such luck. :-)

We'd name our various ORCAD pages things like, "Pg 1- Waveform DAC," "Pg 2-VME Buffers." -- Since there's a separate window that lists all the schematic pages in alphabetical order, wherein you can double-click on any to jump to that page. (ORCAD not being smart enough to have, e.g., hyperlink abilities AFAIK, for, e.g., text placed within a page.)

The the software? :-)