Bad Circuits in the Wild

Hell, just look at Joerg here... he doesn't trust anything with less than, what, two thousand fourty seven sources? Maybe not that many, but definitely mature, very well established parts.

Tim

-- Deep Fryer: A very philosophical monk. Website @

I (knowingly!) have a *lot* of circuits on my website that I know [now] won't work; a few aren't even complete, leaving a complete mystery to the curious reader. Sometimes I strive for accuracy, other times I modify a circuit on the fly, not realizing it won't work (one particular ref: comparator + edge detector + R/S FF = type 2 phase detector, I wired the comparator RCs wrong!).

Of course being the factual type that I am, I early on (i.e. when creating the page) added a disclaimer along the lines of "these circuits probably suck"... ;-p

The motivation behind my list of schematics is to release it for viewing, to show what things I've done. Maybe that's something else you can add to your list.

Tim

P.S. All this talk of circuits is making me think. It's been over three years since I wrote that page. I've got like, a hundred more schematics on this hunk o' junk that could be posted. Some day...

-- Deep Fryer: A very philosophical monk. Website @

it never ceases to amaze me how many bad circuits I see.

One company I am working with at the moment has a product with:

- LV DC input supply

- twisted pair data in & out

- twisted pair clock in & out

- 4 tri-color LEDs

so far their "engineers" have done 27 (nope that aint a typo) revisions, none of which pass EMC.

they have another product whose PSU supposedly is > 92% efficient, but its a triple-conversion (PFC-forward-buck) topology, and the forward converter has been drawn in such a way that it doesnt actually regulate

- the TL431 + opto cause current to flow thru a 10k resistor between

+12V_pfc and 0V_pfc. LOL.

and the same guy who told me it was > 92% efficient (thats a DAMNED good trick for 3-in-a-row) gave me the test spec which clearly shows 70% efficiency and load regulation of +/- 25%

I'd add another: people who *know* they suck at their job (hey, 28th time lucky, right?) immediately get defensive. IME there are 2 ways to respond to criticism: deal with it, or accuse the criticiser of your own failings. Alas the latter is all too common.

Cheers Terry

The Yaesu FTM-10R schematic (included with the radio) is that way... the entire schematic crammed onto two sides of an 8.5"x11" sheet. It does enclose various sections in dashed lines, so you can still figure out what's going on, but it definitely takes a lot more time than if they had drawn the schematic specifically for readability.

You're not the author of The Circuit Designer's Companion, are you, Tim?

---Joel

I wonder... Has it happened yet that some disgruntled designer has gone 'postal' (usenet pun?) and posted all of the electronics IT of a company?

D from BC British Columbia Canada

I looked it up.

7 3/8" hat size is "large". No small mind here.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

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....

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"

Cheers Terry

Heh, no.

Wait, I think someone sent me an electronic copy of that...I should open it some time...

Tim

-- Deep Fryer: A very philosophical monk. Website @

I didn't think so but I figured I'd ask anyway. :-) I know you're pretty young, but these days that means little in writing books... I've been going through Foundations of GTK+ Development a bit lately, by a guy who was all of something like 22 when he wrote it!

It's relatively basic but thorough... especially for people who've just hand the standard college curriculum in electronics, it introduces a lot of important practical issues.

---Joel

Aside from the minor issue that those generalizations are not always appropriate design, they are generally good advice for beginners.

Right! There are a LOT of people who cobbled together a 20-line program in a PIC, and suddenly they think they are a seasoned electrical engineer. Right now there are a BUNCH of guys designing stepper and servo motor drives who have (as far as I can tell) no formal training in electrical engineering, and/or very little practical experience. Some of them are truly amazing in the number of "errors" in the design, or the amazing distance between the published specs and the actual safe operating area of the design. One guy lifted the 25 C one-time pulse specs out of the IR datasheet and then said the drive could sit there all day delivering that at 75 C CASE temperature. (That's the CASE of the whole drive, not even the case of the transistors.) Also had some .05 Ohm 3 W resistors in there with a spec for running the drive at 40 A continuous. Even with 2 resistors in parallel (couldn't tell from the photos I was working from) that is putting 20 W into a 3 W resistor! See how well he could get that by a recognized testing lab!

Other stuff like using 1N4005 diodes as freewheel/undershoot diodes on fast FET bridges, or assuming the ghastly FET body diodes will carry these currents. (Having scoped the results, I've seen the body diodes sit there with 14 V forward bias for over a microsecond before they started to conduct.)

I could go on and bore you with more, but I'll spare you the agony. That is just in one small area that I work at, and know what horrible messes are put on the market.

Jon

O a lot of bone.

So it's you. You're the one...........

Get out the shotgun, Mable. :)

RL

Sheesh! Tell me about it! I once had a job that was ostensibly called "programmer" - I came on board to do firmware maintenance on their product that had a Z-80.

Every single thing on the box was designed wrong! They had AC synchronous motors in a servo loop. The original designer(s?) used stepper motors for precision focus and zoom on a camera thing, with no feedback - i.e., on bootup, the uP drove both stepper motors all the way back to the backstop and then just kept stepping long enough that the programmer would be reassured that it was back at 0. They had an X-Y carriage made of drawer slides. That was the one with the AC synchronous motors in the servo loop.

It paid real good, but they wouldn't let me redesign the thing from scratch, which should have been done. And as a "fringe bennie", they had a stockroom that they had bought by the pound from the previous owners, so whenever I needed a(n?) LED or PN2222 or whatever I could just go and grab as many as I wanted. :-)

I only stayed there a couple of years, and the last I heard, they were out of business.

Cheers! Rich

"Never attribute to malice that which can be explained by stupidity." ---

's_razor ;-)

Cheers! Rich

From

's_razor :

"A practical observation on the risks of stupidity was made by the German General Kurt von Hammerstein-Equord in Truppenführung, 1933: "I divide my officers into four classes; the clever, the lazy, the industrious, and the stupid. Each officer possesses at least two of these qualities. Those who are clever and industrious are fitted for the highest staff appointments. Use can be made of those who are stupid and lazy. The man who is clever and lazy however is for the very highest command; he has the temperament and nerves to deal with all situations. But whoever is stupid and industrious is a menace and must be removed immediately!"

So, where would you put yourself on the diagram:

| Clever | Stupid | |------------|------------| Lazy | A | B | |------------|------------| Industrious | C | D | `------------'------------'

I consider myself "A", clever and lazy. ;-)

Cheers! Rich

I once had a '75 Plymouth Gran Fury with an electrical problem. I found out that the local public library had a wiring diagram for it in their reference section.

It was a stack of "B" size (17" x 11") pages about an inch and a half thick. =:-O

Cheers! Rich

Well, that's a yolk on me! I thought you meant this:

Cheers! Rich

I'm too lazy to post a clever response. :P

D from BC British Columbia Canada