Electronic Design

Bob's Mailbox

Dear Bob: They say doctors make the worst patients, but all my doctors say engineers are the worst. I guess we ask too many questions. I always feel better if I know what's going on. I even like listening to the air-traffic controller, if I can, when flying. Then I know where we are, where we're going, and who's up there with us, even when you can only see clouds.

Anyway, I take several diabetic medications. Some of them have nasty effects if you change or miss dosages. An increase in dosage can make you very hungry, so you overeat, causing higher blood sugar, etc. After a while, it settles down, but the response is a right-half-plane zero—in control jargon.

I test my blood sugar level (BSL) every morning. The tester has a large memory. About every month or so, I plot the data in Excel. The last time I changed medication, my blood sugar got down to 40. This was dangerously low, so I stopped taking it for a while, and it got too high. Finally, the doctor, who I see every three months, prescribed a smaller dose.

I noticed my response to the new dosage had a very nice, two- or three-week time constant. So I decided to try a little biofeedback. I chose a control point of 100 for my morning blood test. If it is above 100, I take that particular medication. If it is below, I don't. It is now very nicely controlled.

If I had to do this through the doctor, the three-month sample rate would turn it into an unstable system. Sampling every day makes it act like a linear control system (like God intended). The doctor expressed no interest at all in my system. All he said was, "Most people figure out how to control their blood sugar."

Like you said, sometimes you are your best doctor. Now all I need to do is listen to the other guy about diet and exercise, and I won't need the pills.
David A. Fox (via e-mail)

Pease: If you can exercise a lot, you might skip a lot of cycles! I take metformin HCl, and it seems to be very mild and not nasty. Before I started taking it, I could not get my BSL down below 160 ±10. As soon as I took the metformin, the average ramped smoothly down to 110 ±10. Now when I am hiking, I just omit the metformin in the morning and let the exercise keep my BSL down. I do take one pill at night. The other night, I forgot to take my evening dose. I realized this when I woke up at 2 a.m., so I went to the kitchen to take half a pill and test myself, to see if I was up at 150 or what. To my surprise, my BSL was at 121—not bad. Apparently, if you can lower your BSL, it makes your pancreas more effective at producing enough insulin, and it makes your body more effective at using the insulin. The best part about taking half the dosage is that you don't have to refill your prescription nearly so often! I do that with my digoxin, aspirin, lasix, etc. But I do not chintz on my potassium. I take three full 550-mg (really 99-mg) pills each morning. This also provides a safety factor, because if I get in trouble from too small a dose, I can go back to a full dose!

Hi Bob: You bring back the good old days when ingenuity was king. Now it's more like a monolithic society regarding electronics (stifling creativity).
George Gatzonis (via e-mail)

Pease: Hi, George. If you look at all the digital junk, of course it is discouraging. Of course it is stifling creativity. Almost all audio and video equipment is made in batches by the millions, with horrifying menus, by "monolithic" Japanese corporations. Electronic music? All done by the menus. But the analog world is not quite so bad. You can still design things that work and are useful and fun. I'm sure some people will argue that if you know how to write code (which I am not likely to learn), you can write some code and wrap it around a small microcontroller, or micropower processor, and invent things that are fun and useful. As for myself, my favorite programming language is solder.

Philbrick Vacuum-Tube Power Supplies: Right now we have five guys interested in buying an old Philbrick "R-300" power supply, 300 mA at ± 300 V—but only one supply. If anybody sees an old Philbrick power supply, such as an R-300, R-100B, R-500, or R-600, let me know, and I can help find it a good home. /rap

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