Electronic Design

Bob's Mailbox

Dear Bob: I have an odd problem. Early British cars used an electromechanical vibrating regulator to supply -10 V to the gas gauge from the 12- to 14-V battery ("positive ground"). The current demand is low, probably 1 A would do. I have been, so far, unsuccessfully searching for a -10-V regulator in a TO220 package. A positive regulator would be trivial to find. I did find an MSK part, but they wanted $100. New mechanical devices are so poor that many are DOA and others have a short life. They cost about $25.

Gene Mallory (via e-mail)

Pease: Hello, Mr. Mallory. Look up the LM337 and see if it won't do your job. It will need 124 ‡, 1%, and 866 ‡, 1% (or 100 ‡ and 700 ‡, 1%). And there you have a -10-V output. It will also want 10 or 20 µF of output bypass capacitance for loop stability and to suppress transients. And if the input source is far away, it will need a couple of microfarads at the -14-V input. And the case of the LM337T will be at -14 V. So, you might need an insulator to couple it to your heatsink. The going price in Akihabara, in Tokyo, is about 79 cents, or 89 yen. They are also stocked by Digikey or similar distributors. (You DID ask the right guy. I designed the LM337T about 28 years ago--and it's still in production. SOLID. /rap)

Dear Bob: While reading your conditioning on the stairs article (electronic design, March 3, p. 20), I was reminded of a friend whose mom conditioned him and his siblings indoors. She put backpacks filled with rocks on her children, then marched them through the house day after day. When she thought they were ready, she marched them out of Lithuania to freedom back in the forties. I think I must have just sat there with my jaw dropped while Ivar told me the story of how he walked to America. Gives homework a whole new meaning.

Peter Nord (via e-mail)

Pease: Hello, Peter. Wow, I am impressed! I read the story of a man and his son who walked from eastern Poland across Europe in the 1930s. When they got to France, the man died, but the son kept going to get on the boat to the U.S. Same idea and also very impressive!

Dear Bob: I never really thought about using the one flight of stairs in my house for conditioning--although I generally climb the steps at work two at a time with only a light grasp of the handrail, as I don't want the safety geeks to get upset. (Here at NSC, some "safety geeks" put up a sign to "always use the handrails to avoid accidents." After I see that sign, I never use the handrails! I always run up and down stairs. But I rarely run down two steps at a time. /rap)

I like bicycling and am convinced this will help build my legs for the hills around here. However, my comment is more aimed at the maximum heartrate issue. I always heard 220 minus your age is an absolute maximum. (You might be quite right, but 200 - x is a good recommended maximum rate. /rap)

Several years ago, after taking a spinning class at a gym and seeing my heartrate hit 175 bpm (at the age of 50), I asked the instructor about this max heartrate thing. She replied that 220 minus age was a good rule of thumb, but people who have regularly exercised for a number of years can usually attain higher readings than the formula predicts.

In case you think I'm just patting myself on the back, I also believe that like any rule of thumb, individual differences exist regardless of other factors. Thanks for the tip on the stairs. I'll probably incorporate it in my own workouts on days off the bike.

Barry Cantor (via e-mail) Pease: Wow. I've done 160 bpm after a long uphill pull, hiking at the age of 60, and I thought I was pushing it. When I walked away from all my buddies back in 2000, at 18,000 ft, I did not have any measure of how fast my heart was beating, but I was definitely limited by how much air I could bring in through my NOSE. I was probably near 160.

ED Online 10307

Comments invited!

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P.O. Box 58090, Santa Clara, CA 95052-8090

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