You may be an old time techie (OTT) if you have any or all of the following: T-Square Drafting instruments Slide rule Drafting machine VTVM RCA Receiving Tube Manual More than 5 Heathkits Simpson 260 Multimeter Any equipment with the Olson, Lafayette or Knight brand name. When I finally got around to upgrading my Ham license to Extra Class a few years ago, I noticed an collective gasp in the class room when I sat down and placed my Dietzgen Log-Log-Decitrig slide rule on the desk in front of me. It doesn't matter what everyone else was thinking, this old man felt like a Jedi Knight... BTW, I never needed the slide rule! John Ferrell http://DixieNC.US ----- Original Message ----- From: "Russell McMahon" To: "PIC List" Sent: Wednesday, February 22, 2006 8:40 PM Subject: [EE] Circuit design & drawing way back when > Copied (as allowed) from Jack Ganssle's latest 'Embedded Muse" > newsletter. All engineers should get this. Even if usually only > skimmed his newsletters are invariably insightful, amusing and, as a > bonus, useful. (Subscribe information at end) > > _______ > > > An insight into the terrible days of how it used to be. Some of us > remember them :-) > > > RM > > ______________ > > > Pre-CAD > ------- > A number of people have been inquiring about an article I wrote long > ago about the pre-CAD days. Here it is: > > Long ago, back in the 70s, there were no personal computers or > similar tools we take for granted. The life of a digital designer was > very different indeed. > > Computer folks used the same tools as civil engineers. Offices were > dominated by the drawing board, a 6 by 3 foot flat panel propped at a > "comfortable" angle. Engineers lived in high chairs strangely > reminiscent of Dicken's Bob Crachet, hunched over the drawing board > with mechanical pencil in hand, creating wonderful silicon inventions > using the same paper and lead that writers and philosophers relied on > for centuries. > > Drafting was a skill all mechanical engineers mastered in college, > but for some reason, at the University of Maryland, it was not > considered important for electronics guys (guys - all guys. There > were virtually no women in the field then). Some engineers were > nothing short of gifted artists, creating schematics that filled the > paper in a visually pleasing way. Others, myself included, could > hardly draw a straight line even with the aid of a drafting machine. > > Lettering was a fine art. It's hard to imagine this now, when we > select from a thousand fonts with a few mouse clicks, but neat signal > names were essential. Some designers used lettering templates. I > always found these too cumbersome, and so subjected all readers of my > drawings to the same illegible scrawl that the nuns weekly punished > me for in grade school. > > Every branch of engineering had its unique set of templates. Digital > designers used a handful of plastic stencils that contained the > entire stock of resources we worked with: AND and OR gates, inverters > and "not" circles, and, of course, various sized squares and > rectangles for microprocessors, memories, and everything else. Large > chips were rare then; the largest might have a whopping 64 pins, > which wasn't too hard to draw. > > We drew resistors, capacitors, and other components using similar > stencils. With a little practice you could whip the pencil through > the zigzag of a resistor template in no time, though a > not-perfectly-sharp pencil always resulted in only a hazy image of the > part. > > Though Luddites scoff that computers let us make mistakes at new, > unprecedented rates, in fact even with these crude tools we were > quite competently creating errors faster than decent designs. In lieu > of a "delete" key we used erasers. Erasers in every form imaginable. > In fact, most of us made so many mistakes we used electric erasers, a > motorized drill-like device that spun a cylinder of gum-like > material. Though these quite effectively removed vast areas of pencil > lead, careless use always produced a hole in the vellum. Then what? I > suppose mil spec folks started over, recopying the entire drawing > onto a fresh sheet of paper. Where I worked we glanced furtively over > the shoulder, and rerouted signals around the hole. > > Drawings produced by hand - by sloppy electronic folks - had much > wider line widths and larger lettering than that we make on computer > screens today. As a result the drawings were big. Though some folks > used "C" size paper (17 by 22 inches) generally "D" (22 by 34) was > the norm. Engineers, production people, and technicians all looked > like quintessential architects, with stacks of these monsters on > every flat surface. When troubleshooting a new design the first step > was to position a big table next to the lab bench - just to hold the > drawings. > > We drew on vellum, a gauzy semi-transparent material that was pretty > tough. It took repeated erasures well, though somehow I always > managed to drill a couple of erasing holes through each drawing. > > Today we use mostly "A" and "B" sized paper, as that's all > laserprinters handle. You can fax or Xerox these drawings without > trouble. An ordinary filing cabinet is the perfect storage place. > Back then, every business had a "drawing room", dedicated to nothing > more than storing (in cabinets called "flat files") and reproducing > these huge representations of our tiny circuits. Most companies had > people whose entire role was to file and copy these. > > No copier then or now could handle a sheet of D sized paper. One > reason we used vellum was its transparency. An engineer duplicating a > drawing first put it on top of an equal-size piece of paper coated > with a light-sensitive chemical, and ran it through the Ozalid > machine. This beast beamed a very intense light through the vellum, > exposing areas with no pencil marks. It then treated the paper with > ammonia, which turned the unexposed areas blue. The ever-present > smell of ammonia (and second hand cigarette smoke!) was simply a part > of the engineering environment. > > Once the ammonia line broke in the middle of the night. In the > morning the entire building was uninhabitable. Fire department fans > eventually sucked the fumes out, but we found strange chemical > changes in our environment. One secretary's fake flowers changed to a > wonderful purple shade. Many pictures hanging on walls now looked > like 19th century daguerreotypes. And, of course, several thousand > dollars of unused Ozalid paper were completely developed, bright blue > reminders of the incident. > > Now drawings have no value. Did you spill coffee on a schematic? Just > print out a new copy. The information itself if immensely valuable, > but its paper incarnation is sacrificial. > > Before CAD systems the paper was the only representation of a > drawing. The labor required to recreate one was so immense that it > was simply inconceivable to lose or mar a schematic. It's funny to > realize that one promise of computerization was the paperless office, > yet what has happened is paper is now so prevalent that it's > worthless. By contrast, in the olden days an original drawing was a > holy relic. Copies were scarce because of the cost of duplication and > the nuisance of storing the bulky papers. > > The regulations said no drawing left the files unless it was being > duplicated or was on an engineer's drafting board. Most of us > flaunted these rules when the Ozalid machine (which required an hour > to warm up) was off at night and we were engaged in a furious > troubleshooting war. Living dangerously, with the original by the > bench, we'd hope to be done by morning when the drawing police came > in. More than one drawing went back in the files with food stains in > the corners. > > I suppose it goes without saying that there were no PCB software > packages. Either our engineers or outside contractors, leaning over a > light table for weeks on end, routed tracks by placing black tape on > sheets of mylar. It was a game of chess: the best board designers > developed a mental plan of attack which (they hoped) would let them > get all of the tracks down without running into dead ends. How things > have changed! Now it's great fun to watch the routing program > automatically plopping traces down onto the virtual board, at a speed > that takes my breath away. In the 70s a big board took weeks, even > months, to design. > > They routed on mylar, as paper isn't dimensionally stable when > subjected to humidity variations, and the PCB was made via a > photographic reduction of the drawing. My dad, a mechanical engineer > from way back, tells me that in the 50s they had the same problem > with paper when designing airplanes. Since this predated even mylar, > they drew on starched linen in ink. Apparently the linen was stable, > but it couldn't tolerate water. One drop of sweat dissolved the > starch, ruining the drawing. And this was before Grumman, his > employer, had air conditioning. > > Me, I'm thankful for modern CAD. I'd never go back to those tedious > days of yore. > >======================================= > > > About The Embedded Muse > ----------------------- > The Embedded Muse is an occasional newsletter sent via email by Jack > Ganssle. Send complaints, comments, and contributions to me at > jack@ganssle.com. > > To subscribe, send a message to majordomo@ganssle.com, with the words > "subscribe embedded email-address" in the body. To unsubscribe, > change the message to "unsubscribe embedded email-address". BUT - > please use YOUR email address in place of "email-address". > > The Embedded Muse is supported by The Ganssle Group, whose mission is > to help embedded folks get better products to market faster. We offer > seminars at your site offering hard-hitting ideas - and action - you > can take now to improve firmware quality and decrease development > time. Contact us at info@ganssle.com for more information. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist