Dear Bob:
I just read your article on knots with great interest (Electronic Design, March 5, p. 142). As an outdoorsman (hunter, fisher, hiker, climber), I'm very interested in knots as well. One knot in particular seems to be a do-all for me. This knot is the basis for all climbing activities. It's the Figure-8 knot. You can tie this knot to create a bight (loop). You could then connect two ropes together. This knot is very safe, and even after being weighted, it's easy to untie. The only true downside is that it's rather bulky and prone to hang up if dragged over an edge.
Daniel Nesthus
via e-mail
Several other people also showed me the Figure-8 with the bight, which looks pretty good. Ashley does list this as #531.—RAP
Dear Bob:
I'm a regular reader of Pease Porridge and I remember reading various articles in which you had written about generating electricity while out backpacking (to charge batteries, etc.). When I saw this flashlight, I thought that you might find it interesting. Here's the link: www.shakelight.com/revamp/. It looks like an LED flashlight that's powered "dynamo-electrically" by shaking. The design looks pretty cool (especially the magnetic "springs") and very robust. Unfortunately, it doesn't appear to be as bright as a real flashlight.
From what I have read in your articles, this seems like the type of device that you may have already investigated. If so, please refer me to the issue in which I might find your comments. If this flashlight is new to you, I would love to hear your opinion of the device.
Joe Miguel
via e-mail
I first heard about this flashlight a few months ago. It has some nice features, but you can't bring it near magnetic tape. I would never have this near my knapsack or my home, as the chance of it erasing my videotape are just too horrifying! It's a neat idea, but obviously to keep it small and light, they didn't put much material into shielding the dc or ac magnetic fields. This isn't for me! Thanks anyhow!—RAP
Hello Bob:
Just recently discovered your series of "What's All This..." articles! Good stuff. In "Floobydust (Part 9)" (Electronic Design, Dec. 4, 2000, p. 141), you were wondering why the Action Light guys recommend lithium/sulfur-dioxide batteries instead of alkalines or re-chargeables. You might have missed this page, where they go a little more in depth about it: www.hdssystems.com/ActionLightTechnology.htm#BatterySystems.
From their table, it looks like alkalines would be a great choice if you plan to never run their light above its medium power setting. Alkalines are a terrible battery technology for high-current applications due to relatively high internal resistance. But they can be very good when asked to deliver low to medium currents. They also seem to want to sell their light as an "anywhere, anytime, no-maintenance" device.
Nonrechargeable lithium cells are great for this purpose because of their extremely long shelf life. Additionally, the particular chemistry they choose will operate over a very wide temperature range (−60°C to 80°C). Finally, the Saft LO26SX has an internal circuit breaker to protect the battery from an external short circuit.
They give you the choice to optimize for your use, though. It looks like you can buy an all-in-one flashlight with space for a single D cell (in which case you must use some kind of lithium chemistry. Otherwise, you won't have enough voltage to run the thing). Or, you can buy a light module with some terminals for hooking up a dc power source. They supply one- and two-cell battery holders and cords for use with this version of the light. In fact, the two-cell holder comes with a pair of alkalines. I suspect another motivation for single D-size lithium on the all-in-one unit is keeping the weight to an absolute minimum because the de-signers originally wanted to build a light for mounting on a caving helmet.
Tim Seufert
via e-mail
Tim, I still say that nonrechargeable lithiums are too expensive, good for astronauts and Everest climbers. Alkalines are cheap and available everywhere. At 1/20 the price of lithiums, they provide 50% of the energy, per ounce, for most uses. Not terrible. Rechargeable lithiums are fine for camcorders and LED flashlights.—RAP
Hi Bob:
I think the basic problem is that energy is too cheap in the U.S. Therefore, it's easy to calculate that it doesn't make any sense to invest in environmentally friendlier stuff. Anyhow, the damage made by cars, power plants, and so on will have to be paid in the future. I don't know who will pay, but I'm pretty sure that one won't have any opportunity to choose.
Heinz F.
via e-mail
Actually, the energy cost is about the same. It's just that in Europe, the politicians have decided to put high taxes on the energy. Now, did these politicians ever give you a chance to vote on whether or not you would like to have high taxes on energy? Or, did they just do it and assume that you would be happy? Our politicians put high taxes on gasoline and energy, even higher than on many of our other consumer goods—just not as high as your taxes.—RAP
All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
rap@galaxy.nsc.com—or:
Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090
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