Electronic Design

Bob's Mailbox

Dear Bob:
I'm enclosing the current issue of the newsletter which I edit for our local skeptics' group. It contains an article of mine about a perpetual motion scam. I don't know if you have encountered this one on your side of the country, but it seems to have been running nationwide for some years. You might be able to make a column out of it. There's lots of information, both pro and con, on the internet. I don't have access myself, but one of my colleagues has been passing material on to me. One link would be via: http://www/voicenet.com/~eric/phact/ which is the PhACT's Web page.

I liked the letter from Robert Nuckolls in the Sept. 16 issue who uses a Tandy Model 100 as a portable computer. I have been doing the same thing myself since since I bought one new around 1983. It makes a perfect portable text input device. I can write outside, in bed, or wherever I please. If I want to pause to think, I can turn it off —reboot time is zero.

I am continually amused by the plaints of portable PC users who have 100-MHz processors, huge hard drives and backlit displays, then wonder why they can only get an hour's life from the battery. I only regret that I didn't buy the smaller, lighter Model 104 when it was being discontinued. (I recently saw a brand new Model 100 on sale at a local hamfest for $110, so they are available.)

I bought the matching Tandy floppy drive, and some years ago, added a 32-K RAM disk to store my most used software without taking up space in the main RAM. At one time, I used the floppy drive extensively when assembling 8085 programs. (One hobby of mine is designing single-board computers round the Intel 8085.) But a few years ago, I wrote my own assembler, in Forth, to run on my Amiga, so I rarely use it any more. Now there's a bunch of maverick traits in one sentence!
TOM NAPIER
North Wales, Penn.

Hoax, scam, rip-off... when a guy claims he's DISCOVERED that an air-conditioner or other heat pump can put out more BTUs than you put in —and ALL he needs to do, is DISCOVER a new heat engine to run off this large amount of heat (at small temp difference) —and ALL he wants is $10,000 of YOUR money to do the research —that's just God's revenge on guys who wouldn't pay attention in Science Class.... Keep up the good work, MAVERICK! —RAP

Dear Bob:
Here's a product suggestion for National Semiconductor: A CMOS 555 timer with an untangled pinout. The problem with the current 555 is that the pinout is awkward. Reset and V+ are almost always tied together, but they're on opposite sides of the DIP. Trigger and Threshold are very often tied together, but they, also are on opposite sides of the DIP. If I had my druthers, the pinout would be:- Ground (as it is now)

  • Trigger (as it is now)
  • Threshold (present pin 6)
  • Discharge (present pin 7)
  • Output (present pin 3)
  • Control voltage (present pin 5, and tell people to bypass it to V+, not ground)
  • Reset (present pin 4, almost always tied to V+)
  • V+ (as it is now)

I think this is the arrangement that would make the common circuits easiest to lay out, but maybe a further improvement is possible. Since a memorable part number helps to sell a product, I suggest naming this one the LMC777 or LMC5555. If it can have some kind of minor improvement in its performance (like the ability to run up to 1 MHz), to establish a market niche, so much the better. What do you think?
MICHAEL A. COVINGTON, PhD
University of Georgia
Artificial Intelligence Center
Athens, Ga.

Michael, that sounds like Genuine Intelligence. While linking from pin 2 to nearby pin 6 ain't hard, connecting pin 4 to pin 8 is an awkward path. However, 25 years of tradition will be hard to break. Your suggestion is a little late! But I'll ask anyhow. —RAP

Dear Bob:
Enjoyed your article on the "Common-Centroid Stuff" in the Oct. 1 issue. However, it was the Fairchild µA725 (not the µA714) that first used this layout technique. As I recall, the sequence of events was as follows:

I had designed the prototype µA725 in 1966 and presented a paper on it at the International Telemetry Conference in Washington in 1967. This early version was quite crude and did not contain a cross-coupled input pair.

When I proposed, and was given the go-ahead to work on, the µA741, the µA725 project was assigned to my officemate, George Erdi. I remember several brainstorming sessions in which we discussed ways to improve on its performance, including the use of a cross-coupled input stage —we didn't have a fancy name like "common-centroid" for it in those days! The sketch we ended up with on the blackboard was very similar to Fig. 2 of your article. George vastly improved on my earlier design, and the product was announced by Fairchild sometime around 1971 (it is not in the 1971 catalog, but does appear in the '73 catalog).

George Erdi subsequently left Fairchild to join Precision Monolithics as a founder, where he designed the very popular OP07, which was the fist three-stage precision amplifier with internal compensation.

The OP07 proved to be so popular that in 1976, Fairchild decided they needed an exact equivalent. TheµA714 number was assigned to the project, and the designer was Joseph Biran, who had joined Fairchild from Precision Monolithics. The mA714 was announced in 1977.
DAVE FULLAGAR
Maxim
Sunnyvale, Calif.

Thanks for telling us the real story, Dave. —RAP

Dear Bob:
As I was reading your Aug. 18 column on copperclad board, I had a few thoughts that you might appreciate. First, on the matter of cost, the best deal is for free. I learned that most electronics companies throw out an amazing amount of this material, usually in the form of scrapped bare boards. In one job, I was able to salvage a stack of about 50 12 x 18-in. boards that had been drilled but not etched, because of an error caught at that stage of the process. As you can guess, the uses that you're talking about won't be affected by an array of 0.040-in. holes. I've also found unetched but slightly corroded material on its way to the dumpster.

I like the selection of uses that you included in your article, and I hope you'll publish more of them as they surface. But here's one that I bet you haven't heard of. With all of this copperclad sitting around the basement, and a groundhog who continually dug his way under the garden fence, I installed a copper barrier, 8-in. above the ground and 8-in. below. The top end is tied to the chicken wire of the fence. I've seen evidence of several attempts to dig under it, but never a successful one. We also had a few groundhogs who could climb over the old fence, but with 8 in. of smooth wall at the bottom, they couldn't get a toehold with their rear paws in order to climb it. If it extends far enough below the surface, this also makes a good barrier against moles.

Here's another one: WE used to have a major problem with squirrels getting into our bird feeder, even though it was hung on a piece of 1/2-in. conduit from the antenna tower, 15 ft. off the ground. The first line of attack was to thread a series of 6-in. sections of golf tubes along the whole length of the horizontal conduit. This made it a bit unstable, but the squirrels learned to make a quick run at it and then cling to the feeder for braking. I also tried replacing the roof of the feeder with 1/8-in. acrylic, which gave them nothing to grab when they landed on the top. But the final solution was to make a barrier about 24 in. in diameter which floats on the horizontal section about half way out, with a 3/4-in. hole through its center. Sort of like an oversized pizza pan. But it's made, of course, with copper-clad board: Two pieces joined edge-to-edge. Since then, only one squirrel has made it all the way to the feeder, but that day the feeder happened to be empty. Poetic justice. I've done other more electronic things with copperclad, but these stories are more fun to tell.
MIKE DEERING
Dimango Products Corp.
Brighton, Mich.

It's always fun to recycle surplus or "waste" materials. The price is right, and we can let our ingenuity run wild —as you demonstrated! —RAP

Dear Bob:
I like your articles, and in the spirit of their titles, I'd like to ask, "What's All This About Professionalism?" I worked hard to get an engineering degree, but if the company feels like it, they can hire a chemist or a physicist as an engineer. Worse, they can even hire a technician as an engineer. So why did I go to college for four years? Lawyers are not interchangeable with MBAs who studied business law, nor are they interchangeable with paralegals. Why is our profession so poorly regarded?
Anonymous

I find an infinite spectrum of good and bad engineers who never graduated from college, and a similar spectrum of ones that did. The odds that a degreed guy can do a task well is slightly better. But many non-degreed guys have a lot of enthusiasm, experience, and perseverance, TOO. I refuse to be prejudiced against guys without an engineering degree. I'm in favor of guys who CAN DO. —RAP

All for now. / Comments invited! RAP / Robert A. Pease / Engineer

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

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