Electronic Design

Bob's Mailbox

Dear Bob:
A reader recently wrote in "Bob's Mailbox" about how small the knobs and buttons are on new instruments (electronic design, Feb. 21, p. 133). I design marine equipment and we just released a new product. Everyone who looks inside asks why we couldn't have made it smaller? Two years ago I established the basic size of the front panel. I put on a pair of diver's gloves to see how closely the connectors could be spaced and still leave room for my fingers. All other dimensions were based on that 1.25-in. benchmark. Sure, it kind of echoes inside that box. But, when your fingers are freezing from digging the ice and sand out of the connectors, it's nice to have things on a human scale.

I designed a small plastic box 15 years ago with some idiot lights to go on the end of a stiff cable. I put in a half-pound brass weight so the cable wouldn't drag the box off the table. I got a lot of grief, but my boss, and mentor, made sure that weight stayed in the design.
via e-mail

Doug, it's wonderful to insist on good HUMAN ENGINEERING in your controls and interfaces. I sincerely hope your customers will support you in the long run! But, would a clamp or sand be better than just brass weight? I don't know. You were there, and I wasn't.—RAP

Dear Mr. Pease:
I recently read a letter that someone sent to you about oscilloscopes and knobs. I, too, really miss knobs. I do a lot of field-service work and sometimes I'm forced to use the customer's scope. Well, a lot of valuable time is wasted trying to set up the scope to trigger, etc. Even the customer doesn't know how to set it up. You may ask why don't you take your own scope? I travel all over the world and it's not very easy to take a scope with you. I want my knobs back! I don't want to have to go three menus deep to set up my triggering or to use the cursors. I can understand menus for portable scopes to save space. But, not for larger scopes. KEVIN SHAR
via e-mail

Kevin, I don't know how to teach all my customers to buy good analog scopes WITH KNOBS. For my good, for your good, and for their own good, they SHOULD. I guess we have to encourage the smart ones !—RAP

Hi Bob:
In the Feb. 21 issue, Stefan Graef wrote to you about instruments with tiny knobs and buttons. You took his argument one step farther and commented on instruments with no knobs. I couldn't agree more. As an experienced two-way radio tech and television engineer, I'm accustomed to using a calibrated RF generator to check FM receiver performance. One technique for doing this is running the attenuator up and down, listening to the squelch characteristics, measuring squelch threshold, 12-dB SINAD, etc.

The current crop of communications system analyzers have no knobs. In particular, the ones from Broken Batwings, known as type M, lack knobs. Everything is menu driven. It's quite obvious that these instruments aren't designed by people who have used one in the real word. Pity.
via e-mail

Bob, I certainly agree that we must buy and use instruments that have SUITABLE controls. Sometimes digital ones are just WRONG. Two weeks ago, we heard how the pendulum is swinging back to real analog interfaces. Digital controls and menus are being rejected. Let's fight back!—RAP

Dear Mr. Pease:
One of the reader letters in your recent column mentioned light-emitting diode (LED) flashlights (electronic design, March 6, p. 138). I thought that I might pass along the web site www.hdssystems.com.It contains some information on a top-end type of flashlight created for spelunkers and others who really care about reliable light. Though it's quite expensive, the web site tells an interesting story about how the flashlight was designed.
via e-mail

Yeah, E. Lee, but this sells for $334, WITH batteries! Unless I was a serious caver, astronaut, or Everest-climber, I'd much rather have two $20 LED flashlights and $280 left over. I just purchased one. Really, one EXCELLENT flashlight is rarely better than two good ones. My technical report will follow soon.—RAP

Dear Bob:
Recently, while transferring a customer's parts list to our internal build sheet, I came across an interesting component spec. We're new to the contract manufacturing scene and it literally saved me the embarrassment of falling asleep due to number-induced mental numbness. This particular list called out a 0-, 5%, 1/10-W SMT resistor!
via e-mail

Well, Joe, for sure you will never find such a resistor out of spec on the LOW side. But because 5% of zero is ZERO, even a measured 5 or 10 m will be out of spec on the high side! Thus, the manufacturer should REFUSE to accept your order until you fix that tolerance! Normally zero-ohm resistors are spec'd not with %, but with 10 or 20 m MAX. So the guy placing the order was probably just using a DUMB computer program that spits out ±5% as a default value, unless otherwise stated.—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

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