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TECHFORUM This is a READER-TO-READER Column. All questions AND answers are submitted by <strong>Nuts</strong> & <strong>Volts</strong> readers and are intended to promote the exchange of ideas and provide assistance for solving problems of a technical nature. Questions are subject to editing and will be published on a space available basis if deemed suitable by the publisher. Answers are submitted by readers and NO GUARANTEES WHATSOEVER are made by the publisher. The implementation of any answer printed in this column may require varying degrees of technical experience and should only be attempted by qualified individuals. Always use common sense and good judgement! All questions and answers should be sent by email to forum@nuts volts.com All diagrams should be computer generated and sent with your submission as an attachment. QUESTIONS To be considered, all questions should relate to one or more of the following: ❶ Circuit Design ❷ Electronic Theory ❸ Problem Solving ❹ Other Similar Topics ■ Be brief but include all pertinent information. If no one knows what you're asking, you won't get any response (and we probably won't print it either). ■ Include your Name, Address, Phone Number, and email. Only your Name, City, and State will be published with the question, but we may need to contact you. ■ No questions will be accepted that offer equipment for sale or equipment wanted to buy. ■ Selected questions will be printed one time on a space available basis. ■ Questions are subject to editing. ANSWERS ■ Include in the subject line of your email, the question number that appears directly below the question you are responding to. ■ Payment of $25.00 will be sent if your answer is printed. Be sure to include your mailing address or we cannot send payment. ■ Only your Name, City, and State, will be printed, unless you say otherwise. If you want your email address included, indicate to that effect. ■ Comments regarding answers printed in this column may be printed in the Reader Feedback section if space allows. 100 March 2006 >>> QUESTIONS I am plagued with trying to determine when my oil burner ignition transformers have died. These step-up transformers generate 9,300 VAC at about 25 mA (new style electronic types aren't a problem: they die dead). In the old days, I used to test them by shorting a screwdriver across the secondary to see if the sparks came from the screwdriver blade or from broken down insulation on the secondary winding (been knocked off my bucket a few times, but not dead yet!) Then they drop to 6-7 kVAC output, and will not reliably ignite the oil burner (though will still ohm out correctly). Does anyone have a good circuit (read: simple and cheap) that can load these and give me a go/no go reading on their efficacy #3061 Anonymous via Internet I am currently interfacing my PIC project to several mains relays using an opto-isolated triac (with zero crossing). The current draw required by the mains relay is only 11 mA and the opto-isolated triac is rated at 100 mA. I am currently using the interface and it works perfectly with no heat from the ICs. My question is: Do I need to use zero crossing for relay control And, I keep hearing about a snubber circuit for inductive loads. Do I really need to use a snubber circuit for just a relay If so, what would be the simplest design In the meantime I will continue to use my interface as it works fine. #3062 Paul Webley Ireland I need cross references to standard part numbers for these RadioShack transistors. RadioShack's website was a lost cause. NPN, RS2010, Silicon, High Gain, 276-2010 PNP, RS2034, Silicon, General Purpose, 276-2034 NPN, RS2042, Silicon, Power, Darlington, 276-2042 #3063 James Tadlock Espanola, NM mr_tadlock@hotmail.com >>>> ANSWERS [#1061 - January 2006] I have six six-volt batteries wired in series to achieve 36 volts. I have tapped the neg to the pos across two batteries and got 12 volts. Can I wire all three (sets of two) and get 12 volts with lots of amps and run a large inverter That would be running series and parallel in one operation. I would have to be using both sources at
READER-TO-READER QUESTIONS AND ANSWERS the same time. Maybe switches would work #1 To safely and efficiently use your 36 volt battery "pack" to run an inverter, you might consider a DC to DC converter. "Solar Converters, Inc." (519-824-5272) www.solarconvert ers.com/ sells Model EQ 12/36-50 that puts out 12 volts regulated DC at 50 amps from a 36 volt DC input. Also check out www.jameco.com Catalog Part #217269CC which takes 19-36 volts DC input and puts out 12 volts @ 12.5 amps. Bob Lindstrom, Broomfield, CO #2 Yes, you can wire the six batteries in series-parallel to obtain 12 volts with lots of amps. You can either parallel three sets of two batteries (in series) each, or else connect in series two sets of three batteries (in parallel) each. Yes, you can use some form of multipole switching to change from a 36V array (series) to a 12V one (series-parallel). What you will not be able to do is to use the two voltages at the same time: The switch will be in either the “36V” position or in the “12V” one. Also, to charge the batteries the switch should be in one of the two positions (according to the charger’s voltage and current). To prevent accidents, you will have to add one pole to your switch so that the charger won’t be connected if the batteries are in the “wrong” configuration. And, of course, the switch should be rated for the system’s voltage and current. To open a DC circuit – even at moderate voltages like 36V – is no easy job. If you want to run your 36V loads and an inverter simultaneously, you should get an inverter that runs on 36V. It will be not only easier to connect, but it will use thinner wires and be more efficient. Ernesto Cerfoglio Buenos Aires, Argentina [#1063 - January 2006] I have a digital caliper. I would like it to display measurements in a third way besides inches and millimeters. Are there digital calipers that have generic microcontrollers that could be reprogrammed or replaced with my own programming If one of them has something like a generic PIC in it, then maybe ... Many digital calipers have a data port hidden under a small cover. You can interface the caliper to a desktop computer using an appropriate cable (ex. Mitutoyo Connecting Cable #905409 www.mitutoyo.com) and a converter box (ex. Smart Cable #200- 50R9F www.qualityonsale.com). This can be an expensive proposition given the cost of the cable is around $40.00 and the cost of the converter box is around $170.00. The good news is that the converter box information comes with a sample Qbasic program that illustrates how to read the caliper value and display it on the screen. Good luck. Bill Ryder Victoria, MN [#1062 - January 2006] I have searched for the Data Sheet on TI's TMS9916NL chip. Any help would be appreciated. #1 The TMS9916 is from Texas Instruments, and it's part of their 9900 series (circa 1978). The 9916 is a Magnetic Bubble Memory controller. The following link provides a brief discussion on the part and its use: www.decodesystems.com/tib 0203.html Briefly, Bubble memory was the first attempt to create RAM that would retain its data after power was removed; a sort of very early Flash memory. Joe O'Brien Ladera Ranch, CA #2 I contacted TI tech support; they were very helpful and found this 25 year old data sheet, which I have posted at: http://us.share.geocities. com/russlk/tms9916.pdf. Russell Kincaid Milford, NH [#2061 - February 2006] Last Fall, we put up a new RadioShack long range VHF/UHF VU-190 antenna and rotator. Correction There was an error in the parts list of my answer (in the January issue) to the Aquarium pump turn off issue. The value of R1 should be 330K, not 3.3K. The corrected parts list: C1 1000 uF 25V D1 1N4001 K1 Omron G6RN-1-DC12 (Mouser P/N 653-G6RN-1-DC12) Q1 2N6427 NPN Darlington (Mouser P/N 512-2N6427) R1 330K R2 680K S1 Push button momentary switch Ed Schick Harrison, NY Around April or May, I noticed that the reception for the higher numbered UHF channels seemed to be getting worse. During Summer, this problem seemed to worsen. Thinking about it carefully now, last Fall we got good to fair reception on channels 36 and 29 and excellent reception on channels 23, 19, and 17. Now it has changed to fair reception on channel 23 and passable on 17. All the others are basically unusable. Clearly, something has changed as the temperature and weather are similar now to when the antenna was installed. VHF reception has not changed since installation and remains very good. #1 You have a bad case of high frequency loss. It is important that you start methodically checking only one suspected part at a time. Here are possible trouble spots: You might have a bad "F" connector at the matching transformer, or the RTV rubber has developed a hairline crack around the coax connector or around the twin lead pigtail on the transformer, letting in water. Silicone does not stick very well to most plastics. Also, with binoculars, look at the connections at the antenna terminal block and the antenna element insulators. Is there any debris such as cobwebs, bird droppings, etc How old is the coax If you used the old stuff, dirt or corrosion at the "F" March 2006 101
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