How do you design these days?

I know one company that does use red wires, so oops's stand out like the sore thumb they are.

Isn't "blue wire" sort of a historic standard ?:-) ...Jim Thompson

In IBM they were known as "yellow wires", not matter what color. The original Teflon WireWrap wires were yellow and the name was kept. I don't even remember what color we use now.

Exactly.

The Scarlet Letter thing.

John

In my best Clint Eastwood imitation voice: "Go ahead, make me drool". :-)

Ed

That *is* what I am doing. But don't you find there is eventually a point of diminishing returns with respect to "paper" analysis and prototyping? The last bug you did have on a rev A board, couldn't you have found it by staring at the design for another week, checking datasheets, going through the operation in your head? Maybe prototyping some more bits of the circuit?

On a sunny day (Fri, 01 Jan 2010 23:20:29 GMT) it happened Jan Panteltje wrote in :

ftp://panteltje.com/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_img_1725.jpg

flat cable on the right:

ftp://panteltje.com/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_inside_img_1727.jpg

EPROM version:

ftp://panteltje.com/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_8049_programmer_board_img_1731.jpg

RS232 connectors,

ftp://panteltje.com/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_rear_img_1728.jpg

use....

uses the DIN 5 pole to

Hey, I got that old MCS BASIC computer working again:-) grml: ~ # ptlrc -d /dev/ttyS0 -b 1200 Panteltje ptlrc-0.6 using device /dev/ttyS0 Escape exits.

READY

All I needed to do is solder back some wires to the connectors that were broken.. The NICAD charges and is still working OK! I could no longer find the manual for the 8052AH MCS BASIC, but is not internet and google great: wget

Nice, an other computer online. Also once wrote an a very simple assembler for that 8052AH, it can output asm in MCS BASIC data statements, so you can speed up parts of the BASIC code:

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I tend to spec the part number with a -(any) on the end for color. Batch to batch from production will have different colors. The number of jumpers has dropped to maybe one or two at the most. The most common has always been the missed connection in the layout or schematic. If you call a power supply "+24V" in one place and "+24" in another, they are (no surprise) not connected. I now make it a rule to always check my supply naming as the last check before layout.

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I've seen people who color code revisions (mostly in WireWrap, though) and power/ground/signal jumpers. I'll still use color coded wires for (the few) prototypes I do.

An easy check for this sot of error is a sorted netlist. Perusing a sorted netlist will find all sorts of otherwise difficult to find errors ('l's instead of '1's, '0'/'O',...). If a net is misspelled it'll show up twice.

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PC

We had one of those PCB mills, on indefinite loan from a customer who wasn't using it. It was such a hassle that we wound up not using it too.

I can do the modest stuff with a knife and some kapton tape. After that, it's easiest to just lay out a board and have a pcb house make a few.

Teflon board material is a lot easier to x-acto than FR4. You can get it on ebay.

John

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It helps to print out a net list and read it. If you see VREF and REFV, investigate!

One mistake we used to make too often was swapping V+ and V- on opamps. Engineers tend to flip an opamp to make the feedback path look nice (different for inverting/noninverting) and that moves the power pins too. We check that really hard now.

We *almost* made some boards that had the BGA pitch wrong, due to some metric/inch rounding error that got us 3/4 of a ball wrong across the whole chip. Caught that by accident before it got out.

I'm always a little anxious until the first successful powerup, and then until the uP runs code, and then until the FPGA configures, and then...

On a recent board, there came a point when Linux was talking through PCI Express to our FPGA, and everybody cheered.

John

Fire extinguishers usually do. ;-)

Sure, there's a point of diminishing return. But a tradeoff of a week of checking to avoid a board spin is clearly worth it. Most of the time, in hardware or software, a bug just makes you look at an error that was in plain sight and would have been prevented by checking. We check enough that maybe 80% or so of our boards are sellable at first etch. I suspect we could do a little better, 90% maybe, and that would be worth it.

The Brat is working on a checklist for design review to formalize our release process. There will be something like 40 items on it.

John

Gotta be better than fence clamped to a drill press.

You mean copper-clad kapton tape? We use kapton tape as an insulator.

Maybe I'll try it, but I don't do much prototyping. We have a prototyping machine but bringing it up has always been on the "to do" list.

What do you can an insane price? Loads of compagnies sell similar stuff. FR4 is actually cheaper then phenolic.

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We've done that too. The boss caught it last time. In that case the layout guy screwed up the library. I also made him add an alternative view for all op-amps so I can show them either way and still have the power pins in the right place. It was a lot cheaper than a board spin (with no other information gained).

That's something I'd never find.

You're done, aren't you? ;-)

Beer time.

We usually hand-build a prototype of the "first etch", and use it as a development board for the firmware. After fixing any remaining bugs, I am then sufficiently confident of the design to go to "production" (typically only 50-100pcs for our stuff). This is actually the most expensive cost, the solder stencil costs more than the bare boards!

I suppose it depends on the board, but for us that hypothetical week of extra checking to avoid a board spin would *not* normally be worth it. We wouldn't be confident enough to go straight to a production run, so would still need to hand-make a prototype. Sure, "getting it right first time" would save us a couple of hundred dollars in NRE, but cost us up to a week of engineering time in this scenario.

That's what I do, go through a checklist. If a bug ever makes it through

- or nearly does - that "class" of bug gets added to the list. It's useful, although time consuming.

With the spindle Morse taper Loctited in so that the side forces don't loosen it up!

Best regards, Spehro Pefhany