Re: USB microscopes for very small SMT

krw wrote:
In article <7Zc%k.7873$as4.1969@xxxxxxxxxxxxxxxxxxxx>, notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx says...>
Joel Koltner wrote:
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message news:TQz_k.9442$c45.3508@xxxxxxxxxxxxxxxxxxxxxxx
For example, one classic mistake I find in my consulting practice is the use of too high impedances in low-energy sensing circuits. A little moisture, a little dirt, and it'll be on the fritz. The right way is to use low impedances and then pulse-measure. But it seems universities don't teach that stuff anymore.
They're concentrating on "low power" (what every laptop needs, right?) so the students naturally gravitate towards high-impedance designs...

Laptop designers seemed to have "un-learned" that as well. Until recently when the Intel Atom came out and (some) laptop designers "re-learned" the art. When Howard here in the NG mentioned the Samsung NC-10 and I saw it gets >6h, like my old Compaq Contura used to, I honored that laptop performance with an order. Seems others have done the same since I initially received a backorder notice despite the fact that "in stock" was mentioned. Should arrive in a few days :-)

6hr batter life isn't the only design point for laptops. Many/most are being used as desktop replacements, so battery life is *maybe* a secondary parameter. In my case, two hours is good enough but I need high resolution, external display capability, large disk(s), and all the other stuff that used to be the sole domain of desktops. Sure, I'd like a three day battery, but I'm not going to give up any other aspects of my laptop to get it. In fact, newer laptops *are* better than those of five or six years ago, taking all of the parameters into account.


Well, for desktop jobs in the office I use ... a desktop.


I often encounter folks who are quite unfamiliar with the scheme of saving battery power via pulse action instead of high impedance.

The designers of these devices are well aware of these power-saving schemes, and far more. ...


When I see a fan and hot air coming out of a laptop no matter what you set in the "energy management" tab I do have my doubts here. For example, the old Compaq could throttle the uP down to a few MHz. That's how they got 6h out of a standard old-tech NiCd. For years. Until all the rough flights and nail-it-to-the-runway landings caused the frame of this laptop to fracture :-(


... It's a matter of design (and that necessarily means marketing) priorities.

Sometimes it's necessary that engineers question decisions by marketing. Got to be careful here, since I married a marketeer ;-)


Students need to re-learn the old art of obtaining some of their wisdom from non-academic sources. I'd venture to say that >50% of the knowledge I use in my practice is from non-academic sources. App notes, Internet, ARRL books and such.

This stuff is standard design practice. There aren't any secrets here. The processor datasheets lay it all out. Do not, however that a given computation has a minimum power requirement. If you draw that time out (your "pulse action") you only waste more energy.


That's what I thought as well, that folks know this. But, example: "Don't you have to keep the bridge current running until you are sure the uC code has finished and can read the ADC?" ... "No, the value is being stored." ... "But it can't be, the code may not have gotten to that point." ... "See that 74HC4051 there? It's set up as track-and-hold so the value will be stored in the film cap over there." ... "Oh."

--
Regards, Joerg

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