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By Design News Staff -- Design News, January 12, 2004
THE POWER OF FRUIT
At first I was impressed by the grapefruit-powered thermometer (DN BUZZ 11.03.03). However, the statement, "Okay, he sort of cheated when he used a grapefruit" is an understatement, because in the design small print it says, "Sometimes, the grapefruit may not be able to provide enough current to start the onboard charge pump. In this case, connect a single-cell AA or AAA battery momentarily, until the system starts." Yuk! I say back to the drawing board. This article was not ready for publishing.
Jim Hartmann MINNEAPOLIS, MN
Inventor Guarang Kavaiya's response: Jim, it is obvious to me from your acidic response that you have discovered the sad truth—not all grapefruit are created equal. Allow me to help you overcome your case of grapefruit envy with a little journey through "Mr. Wizard's World" to explain why your fruit fell flat. The whole voltage-generation method for utilizing a grapefruit power source is based on a slow chemical process. It takes time for the process to start and stabilize, resulting in a slower voltage build-up. In this design, we are using a charge-pump device to multiply the lower voltage generated by fruit into a usable voltage range for the LCD device. Typically, charge pumps have one limiting characteristic—they need input voltage to be within a specific range. If input is outside this range, it will affect the efficiency of the system. Given this set of parameters, here is what happens: The grapefruit slowly builds voltage. If you connect the charge-pump circuitry while the grapefruit's voltage is building, the available voltage will be lower than is required; the charge-pump's efficiency will drop; and it will draw too much current. Since the grapefruit cannot supply this much current, the system cannot recover. Momentary battery contact puts the charge pump in high-efficiency mode and allows the grapefruit to pick up as the sole power source. So is this a problem with every grapefruit-thermometer system? No. This depends mainly on the type of fruit, metal plates, and given stabilization time, among other factors. Pure metal plates (zinc and copper) create a much better battery cell. However, these plates are costly and difficult to obtain (especially zinc). If you do not have all of these ideal components and you must connect the system immediately (rather than waiting for the grapefruit's voltage to build), then one of the easier options is to use a battery "jump-start" mechanism. This issue is related to the closed-loop effect created by the non-microcontroller and fruit elements of the thermometer system. Keep in mind that this grapefruit thermometer easily runs for four to five days straight on the same two fruits. If you were living in a remote area without a reliable power source and were dying to know the temperature, I doubt you would be saying "yuk" to just a few seconds of AA-battery contact.
HACKERS OF ANOTHER SORT
Your editorial on writing (DN MY VIEW 10.30.03) was right on! I've noticed a definite downward spiral in the quality of the written word in just the past year. People bang out emails and articles as fast as they can and send them off. I get messages every day from bright, educated engineers that are so badly hacked, I need to call them to find out what they really mean. I read news articles on the web and in print missing words in sentences, including multiple verbs in a row, and putting punctuation in the wrong places. No one proofreads. I write well (usually) and I'm often complimented for it because good writing is becoming a scarce commodity.
Tim Lange ANOKA, MN
SAAAAY WHAT??
One example of bad writing that caught my eye appeared in the technical rationale portion of a proposed standards revision being routed around for approval. The statement was, "It is difficult to measure the depth of the notches, any "dabree" in the notch will give a measurement error . . ." After my initial shock, I understood their phonetic attempt at the word "debris."
Dennis H. Roat WITCHITA, KS
SPELLCHECKER FIASCO
I have a funny story to pass along regarding the use of Spellchecker. We recently received an email from a young graduate with an attached resume. Within the text of the e-mail, he stated that "our location would be excellent for him" since he had some family in the area. Unfortunately for him, however, he had accidentally spelled location beginning with "lac." His next mistake was to rely on spell checker to automatically replace his misspellings with the appropriate word without scrutinizing each message box that popped up. The resulting "your lactation is excellent for me" certainly did not do justice to his intent. On top of that, our HR director recently had a baby girl and is still nursing!
Dan Rebeck HAYDEN LAKE, ID
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