原创 Start with basics then move to complicated stuff

You have most likely read our own inscrutable Max Maxfield's recent post on iPod/iPad/iPhone headphone output. He started by explaining some fairly fundamental analog concepts.

I emailed Max asking why he'd started off at such a simple level. He replied that, over time, he's come to realize it's not a good idea to assume everyone understands everything, including the simple stuff. A lot of EE Times Asia community members are students. A lot of members focus on the digital domain, as opposed to analog, and many professional engineers have forgotten a lot of the fundamental concepts they no longer use on a day-to-day basis.

Almost as soon as I'd read Max's response (some might say coincidentally), I received a request for help from a friend who wanted to connect a LED to a 12VAC power source. This friend is a particularly bright guy with an MSEE, but he left engineering and went to "the Dark Side" (project management) about 30 years ago.

It's amazing what we forget. My friend sort of acknowledged this by starting with a bit of humor. "I was hoping that, if I connected the LED to the AC just with the resistor, it would work, but maybe not be as bright," he said. "But I guess, being AC, the reverse voltage causes the current to flow the other way -- who knows with modern LEDs these days, anything can happen -- causing the LED to glow bright black in the negative cycle, and the eye would cancel all of the bright white and the bright black, and we'd see nothing."

I explained how to calculate the current when using a LED. I also explained that he would have to protect the LED with a diode in reverse polarity across the LED. He came up with the following circuit based on my description.

 

Observe the "+" and "-" annotations marked on the AC. Also observe that no current will ever flow. We all can see that, right?

Then I started to think of other instances when I've been surprised by people's lack of knowledge. Six or seven years ago, we hired an EE graduate straight out of university. A few months later, I was reading a Jack Ganssle blog post, from which I've extracted the following quote:

Long ago I worked with an engineer who had applied for a job at Cape Canaveral. The tour seemed to always come back to a panel of beautiful controls just crying out for some tactile interaction. A big bundle of wires coming trailing on the floor was cut, proving the box wasn't connected to anything, and my friend finally succumbed and twisted a knob. Klaxons suddenly blared all over the blockhouse! The panel was a test; management didn't want to hire someone who pressed buttons in a launch complex. He didn't get the job.

I found this very amusing, so I told the story to the guys in the lab. They all laughed, except the young guy who asked, "What's Cape Canaveral?" (He didn't know what Cape Kennedy was, either.)

The bottom line is that there is a lot of stuff we don't know, some stuff we forget, and some stuff we must pass on to other generations. So all I can say is "Keep up the good work, Max."

How about you? Have there been any occasions when you discovered that you'd forgotten some fundamental concept? How about someone being ignorant of something you would absolutely have assumed that person knew?

Aubrey Kagan

Engineering Manager

Emphatec