Re: Bad Circuits in the Wild

Joel Koltner wrote:
"Bob Eld" <nsmontassoc@xxxxxxxxx> wrote in message news:dBrVj.3384$nl7.2448@xxxxxxxxxxxxxxxxxxxxxxx

I disagree, you can put all kinds of fail safes in the code plus multiple
redundancies, even multiple processors, voting routines and other tricks to
improve reliability.


You could make the same argument for the "core" of a traditional (analog) motor controller. I think you'd be opening yourself up to a lot of liability if you didn't take the (traditional) approach of using (relatively) physically separate circuits -- even if they're implemented digitally in the form of, e.g., little "supervisory" CPUs -- to independently watch for fault conditions. I wouldn't personally market a motor controller that didn't have such features! (Something like the device Joerg worked on where the CPU just died if you stopped the clock... that's arguably "reasonable," -- in that no one gets hurt just because a few tiny transistors fry. It's the cases where the potential failure of a system can be "reasonably" expected to result in physical injury to other people or devices where you need to start adding that robustness to avoid liability problems... You're aware that every major IC manufacturer out there requires written approval from the president or similar before they'll sell you parts to use in life-support equipment, nuke reactors, etc., right?)


real example: one of our control boffins had a habit of pressing the pause button on the 80C196 ICE, every time he needed to think. If we didnt have hardware interlock and over-current protection, every time he did that the hardware would die. Because we had the relevant hardware (which is cheap and easy to design) the unit just kept working (although the motor makes a loud "klonk" noise as it rapidly grinds to a halt).

I once tested a little Toshiba drive - 3/4 hp IIRC. we were astounded at the puny DC bus cap, until I found the note buried in the back of the manual that stated it has to be replaced every year. And when we ran the machine into a stall, the drive blew up. three drives in a row did that. And our marketing department wondered why it was so cheap....


If you put a .45 slug in it, it dies, so what? If you put a .45 slug in you,
you die too!


Human physiology is not always as robust as I'd like. :-)


I read an interesting article in an Inside Kung Fu magazine that claimed 10% of gunshot victims die, c.f. 30% of stabbing victims. and the average length of a fatal stab wound is 1.75"


BTW fix your power supply, there's something wrong with it.


I'm convinced it's working 100% "as designed." It's just that the design isn't robust!



Cheers
Terry
.

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