On Tuesday 19 October 2021 00:46:09 [email protected] wrote: > On 09.10.21 02:31, Gene Heskett wrote: > > On Friday 08 October 2021 21:15:12 John Dammeyer wrote: > > > I disagree. Grounding won't fix what is inherently a bad design. > > > Might make it appear less often if that indeed is the reason but > > it's > > > > still a bad design. > > > > HAving taken a third look at that link, I have to agree. That family > > of > > > chips have a proclivity to set off a substrate scr, which can muck > > up > > > the logic or even crowbar the power supply when an input pin is > > pulled > > > above the supply line, a possibility given that the encoder is > > running > > > on 12 volts and the 74hc4050 is on 5 volts. Bad dog, no biscuit. > > Yup, been bitten by that one too. Back in '78 I took over a supposedly > complete digital clock design for supply to Ford. But they reported > that > "Your clock is dead the second time we turn it on." A drive to their > proving grounds, where the prototype XD Falcons were being put through > their paces, and some probing with a storage scope, showed a -1 kV > transient on the accessories line on ignition switch-off, due to a > couple of relay coils. That led to: > > Q: "What's wrong with your flyback diodes?" > A: "What are flyback diodes?" > > We drove back to Melbourne from out near Geelong, my boss and his went > home, and I sat in the design lab with the instruction "Fix it, but > it's > not allowed to cost anything. The product price is fixed by contract." > > It took a couple of hours, but the data book's logic family > characteristics section revealed that if I limited the current of the > input overvoltage to a few mA, then the parasitic SCR wouldn't latch. > The 220 kOhm resistor I added on the CMOS input did cost a cent at the > time, but they allowed me that. My recollection is that we just sent > the > new prototypes, and waited for confirmation that our clocks were now > automotive compatible. > > What boggles my mind is that on that day, the scope trace was recorded > with a polaroid camera bolted over the high persistence CRT screen. > Now > we don't have CRTs or film cameras, EVs drive themselves, and fossil > fuelled cars are set to not be mass manufactured by the end of the > decade at the latest - due to having been more expensive to own for > more > than half the decade. (Well, from now, if you can get delivery of an > Xpeng 5 or BYD Dolphin or ...) OK, it doesn't help when VW takes 30 > hrs > to build a car, while Tesla does it in 10, for a projected > fully-on-line > output of 10,000 cars per week from the Grünheide factory alone. VW > is > already planning 30,000 layoffs in order to avoid bankruptcy as they > hand over European #1 carmaker title to Tesla, and try to avoid doing > a > Kodak. Just wait till the Texas factory arcs up. > > Erik
TL; DR. Sometimes old memories spit out something useful. I spent a couple years as the ACE at KRCR-TV in Redding CA, back in what would be the infancy years of character generators. They had a getting elderly one made by 3M that was full of the 4000 family of cmos logic. It badly needed a borderline around the basic characters it generated, due to the bandwidth limitations of NTSC. I designed and built a borderline generator that even allowed the border to be colorized. But to get the speed it needed to work well it had to run on the full 28 volt supply available in that chassis. Thats well above the ratings of the 4000 family. So I built it anyway, it ran a little warm, and 2 years later it was still running a little warm. It turned out the border generator made its best contribution to the readability of its output, if the color of the border was chosen to be the reverse of the characters color. That, combined with the bandwidth limitations imposed by NTSC, essentially canceled the ringing of the edges of a character and made it more readable on the average tv of 1980. Thats the same station that had an automatic station break controller, but no generator for the queue tones it needed to trigger the next tape player. So my first ever computer driven project was made from a Quest Super Elf, an rca 1802 driven board. It came with a hex monitor, no assembler. What they needed was made by a master tape that was in pretty bad shape, they were dubbing a copy of it to a blank tape, then dubbing the finished commercial onto that. So with all that dubbing on 3/4" u-matic video machines of the day, you couldn't tell a lawn mower from a seed broadcaster in the image. So I proposed to make a computer do all that to the finished commercial, doing away with 2 generations of dubbing in the process. Much better on air video. So I learned how to program an 1802 by looking up the nemonic in the programmers manual, and entering the code via the boards hex monitor. But the board only came with 256 bytes of memory, so I had to order, and build, an S-100 bus backplane, and a ram board with 4k of static ram on it, $400 for 4k in those days. I wrote it such that a pendant with a bunch of pushbuttons on it to set it for the the standard lengths of commercial times up to 2 minutes, and once that preprogram was set, a final do it button. The final icing on the cake was to replace the then standard "academy leader" with the countdown to air image down to 2 seconds before the first frame of video to air from the tape. So I built a huge character generator in 8.8 digital format so they could see it on a 5" monitor 20 feet away in the control room. Stole a audio cart recorder that was off speed to make copies of my program so it could be reloaded after a power failure. It was a huge step up for the production people. Then I went down the road looking for greener grass and found some. 17 years later, I'm a Chief Enginneer myself, brought my then new wife to oregon as a vacation, staying with a retired aunt in Salem for a week or so, where I played handyman around her place, and while I was there, called down to Redding to talk to my old CE, who claimed they were still using it 17 years later! In a tv station control room, thats a couple eons! Blew me away. But I had kept a cart with the program, and a paper copy of it in case I ever needed to make another. Still have it all in a 10 by 13" freezer bag on a shelf above me 41 years later. At the next annual NAB convention, I mentioned to the Microtime folks who had the bare bones of such a gismo on the table, and bragged that I had already done that. Half an hour later I came back by and it was missing. And I guess they'd bagged it and took it back to the truck, never to be seen again. Somebody had beat them to it. I have to chuckle everytime I remember that. Now I'm an old man of 87, 20 yers retired from that CE position, a widower again (3d time) as that lady, standing beside me in the pix on my web page, link in the sig, in a now 17 yo pix, passed from COPD last Pearl Harbor day. Thanks for reading his far. Take care and stay well folks. Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
