Electronic Design

Bob's Mailbox

Dear Bob:
I have enjoyed your column for many years. I also am an analog guy, working as the chief engineer for a PBS station.

As an avid boater, Douglas Butler caught my attention (electronic design, May 15, p. 135). I cannot find a marine radio large enough for a decent user interface. Knobs are small, or worse yet, up/down buttons. Changing channels by pushing the up button 20 times is insane. Even worse is the speaker. A 2- to 3-in. loudspeaker cannot move enough air to be heard while under way in a power boat. So, you have to buy an external speaker that costs more and takes up more room. I got lucky, and found and repaired a 20-year-old Regency radio with a 5-in. speaker, decent knobs, and direct channel entry.
Bill Schwartz
via e-mail

It sounds like you used SCROUNGING to find a good solution! Furthermore, you found a good old radio with PROVEN reliability. If it has lasted this far, it should be reliable a good bit LONGER!—RAP

Dear Bob:
Here's another interesting Analog vs. Digital debacle: I recently read that a certain company in Texas is trying to push digital projection systems into movie theatres around the country. Disney is currently releasing a feature film around the country to showcase this technology. Worldwide movie distribution will be revolutionized, and customers will get incredible digital quality. All is great, right? Wrong!

Although the technology will bring many benefits and cost reductions to studios, distribution houses, and large cinema conglomerates, there are certain very significant disadvantages from a consumer point of view:

The current systems support only 1 million pixels. That's a huge step backward from the 35-mm analog format that has up to 4000- by 3000-pixel resolution. It doesn't even compare to the roughly 2 million pixels of digital TV, available at your local electronics store.
via e-mail

H'mmm—the digital guys are trying to swindle us again, eh?—RAP

Dear Bob:
I'm not a circuit designer by any stretch of the imagination, but I just have to know if the 0- resistor is real. I never heard of such a thing. If I had, I would have put it into the same category as the darkness-emitting diode (DED). Your reply implies that they exist, so I just have to know—why?
ABB (Another Bearded Bob)
via e-mail

OF COURSE there are "0- resistors." They have been around for over 30 years. They act like a jumper. But, as they are the same as a standard resistor in size, they are easier to handle than a jumper. Look them up in any decent catalog, like Digi-Key, Newark, Allied, etc.—RAP

Hi Bob:
It isn't often that I catch you in a blunder, but I think I have now. Your comments that a "DUMB computer program" spits out 5% as a default value isn't true. I used to use 0- resistors a lot, but I was never a distributor for any. If you think about it, all distributors price resistors by tolerance. So a 0- resistor can't be 5% out, but he's telling the sales people to sell them at the same price as a 5% resistor. Now that you realize this, ain't you ashamed?
Joe Stern
via e-mail

Joe, I'll be darned if I'll pay any more than the "20%" price for these cheap resistors. If someone wants to charge the "5%" price, then they won't get any business from me! Best Regards.—RAP

Dear Bob:
I, too, liked your article on knobs vs. menus. But it's worse than you made it seem. It's really about analog versus digital scopes. Analog scopes show you the "real" waveform. Digital scopes show you what some computer chip thought some analog-to-digital converter thought it saw at some point in time—averaged/sampled, or whatever, over some period of time.

Generally, I find it very difficult to troubleshoot a circuit with a digital scope. The thing takes forever to sync, and just about can't display anything but a clean repetitive waveform. Almost ALL waveforms have noise on them (when I know I have no noise), which I have to mentally subtract out.

About the only thing a digital scope is good for is getting numerical data on the waveform (rise time, etc.). So I keep both kinds of scopes on my bench, as do most of the people I work with.
Tom Mills
via e-mail

Of course, you are GENERALLY RIGHT. I agree. But, you also will agree that for certain rare cases, a FAST digital scope is JUST RIGHT, and better than an analog scope—sometimes even better than an analog Memory Scope. About once or twice a year, RIGHT?—RAP

Dear Bob:
This link: www.alibris.com/ is to a company called Alibris that buys and sells out-of-print books. I hope this helps your searching.
Richard M. Saur
via e-mail

I will try on the "Farm Journal Pie Cookbook." Hey, they seem to have it. I may try to buy TWO—and, "A Race On The Edge Of Time." They are doing at least as well as Amazon. Thanks, Richard!—RAP

All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
[email protected]–or:

Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090

TAGS: Digi-Key
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