Nerd's Corner We try hard to keep the info in Home Power accessible to anyone who managed to stay awake during high school science. And all of you techies cuss us out for not getting down with some heavy nerding on high tech stuff. Well, here it is: a column that assumes that you are experienced. This column is for electronic and computer techies to get as complicated as necessary without providing basic access for non-electronic types. Damn the transistors, full speed ahead! The Hewlett-Packard DeskWriter Printer- a high res printer that loves inverters! We use Macintoshª computers to publish Home Power Magazine. We've never been flush enough to afford our own LaserPrinter. In order to print the masters for an issue of Home Power, we bundle up all our computer gear and go to town where we rent a LaserPrinter and hope everything comes out right (which is never hasÉ). We've dreamed of having our own printer and were alarmed to hear of a LaserPrinter frying and dying instantly on inverter power. Something to do with the essential incompatibility of thyristor power control and non-sinusoidal ac electricityÉ Is there anyone out there successfully running a laser printer powered by an inverter? Now a laser printer consumes almost 900 watts when operating. We went looking for alternatives. We discovered a 300 dpi ink jet printer made by Hewlett-Packard that is specifically designed to work with Mac computers. We paid our bucks ($885) and held our breath. The HP DeskWriter is powered via an oversized wall cube. The printer functions well, with no heat buildup, from inverter power. It consumes 26 watts while printing and less than 4 watts in standby. We were impressed. Quite a difference from the kilowatt consumed by laser printers. But the proof of the pudding is in the printing. We were astounded to see printed output from the DeskWriter that is comparable with laser printers. Graphics done at 300 dpi reproduce faithfully on the DeskWriter. The pixels are squarer than laser pixels and dimensions are truer to life. The DeskWriter is not a Postscriptª printer, but speaks QuickDrawª, the heart of the Mac graphics system. As a QuickDraw native, the DeskWriter prints more faithfully what is shown on the screen. And it does it faster. We decided to give it a tough task printing Stan Krute's illustration on page 4 of HP13. This illustration is full of 300 dpi dots and choaked the laser printer. Our page layout program refused repeatedly to print the image on the laser while giving cryptic screen messages like "Unknown Postscript Printing Error". The DeskWriter consumed the image and printed it in less than a minute. It took the laser over 3 minutes to decide that it wasn't going to print the image at all. The DeskWriter performs glitchlessly with all our software (RSG4.5, SuperPaint2.0., Excel2.0, Word4.0, and MacDrawII). The DeskWriter printer is very quiet when printing. It is cheaper to use (in terms of electricity, paper and ink) than our 72 dpi dot matrix ImageWriter. The DeskWriter costs about 1/2 to 1/4 of a laser printer and consumes about 97% less power. And how does it look? Well, you've been reading its output reproduced on this newsprint. We used the DeskWriter to make the masters for this issue. No trip to town, no massive power consumption, and no gastric ulcers because everything printed properly the very first time! Richard Perez More on Inverters and Electronics This is in response to the HP13 letter about TV interference. I'm running an RCA portable VCR docked into its 120 vac tuner/timer unit, feeding video (not modulated RF) directly to a Mitsubishi 1371A computer monitor (I can't imagine why anyone would want HDTV after seeing the beautiful picture this gives!). Watching broadcast stations on generator power always worked fine, but running on my Heart HF24-2500X inverter I would always get more and more noise (short horizontal lines) in the picture as the battery voltage increased. By midday, the PVs raised the battery voltage to the point where the picture was totally overloaded with noise and the screen would go black. Running the antenna rotor also caused this kind of interference. Running either the VCR or the monitor on a separate inverter would cure the problem. Finally, I found that a big EMI filter, with four 3mH chokes and some capacitors inside, installed between the inverter and the VCR tuner/timer, and a smaller filter installed on the power cord to the rotor, solved all interference problems. EMI filters are commonly used in computer equipment (the monitor already has one, but not big enough to deal with the inverter power) and are available at many surplus outlets. You must connect the ground wire as well as the power wires to get full effect. You may have to try several filters before finding the right size, and one which does not buzz obtrusively. The one which solved my problems is about 1.5" X 2" X 2.5 - bigger than most. While playing with this filter, I discovered that a smaller 4 @ 1.6 mH filter left plugged into the inverter almost eliminates the nasty audible buzz on idle, and adds on 30mA. to the inverter's idle current. AND- a report on the Telenexus phone line extender I have a 1.5 mile clear path for the radiotelephone link, which is very easy for the 2 Watt Telenexus units. The phone line end is on a pole in the middle of a field, with its own PV panel and battery. I brought the units home, wired them up, and everything worked the first time! Then I tried using a computer and modemÉ Neither Apple's "Personal Modem" nor a U.S. Robotics "Password" would work at 1200 baud. After reading an InfoWorld test of modems, I bought their highest rated Multitech "MultiModem 244EH" and was immediately able to run 1200 or 2400 baud and connect MNP error correction! When you are out on the raggedy end of the phone network, there are VERY significant differences between different brands of modems. Also connected to my end of the Telenexus is an AT&T HT-5500 cordless phone. It comes with a wall transformer marked 14 VDC, which actually puts our a measured 17+ VDC, but the phone works fine connected directly to a 12 Volt battery. No polarity problems, no interference, and no noticeable reduction in range. As always, it is wise to add reverse voltage protection diodes when hacking on devices not intended for 12 Volt use. There is (wouldn't you know) one flaw- the phone uses "short tomes", meaning that no matter how long you hold down the push buttons, the "touch- tones" are only 1/1000 second in duration. Sometimes my central office doesn't hear them properly, and I can't be sure if it is because they are short, or not loud enough, or off frequency. I have been comparing various phones and find a wide variation in the pitches of the tones they make! I'm sure standards and tolerances for such things- does anyone know where to find them? The hardest part of installing the Telenexus was convincing the phone company they had connected me to a defective wireline! It took almost two months of complaining and listening to them say my intermittent noises were in the radio system, before they sent out a top techie and solved the problem of stray voltage in their wireline. Pac Bell's tech finally admitted my Telenexus provided a cleaner connection than the best wireline he could hook it to out here in Northwest Nowhere! Thank you for your invaluable forum! Loren Amelang, Box 24, Philo, CA 95466-0024 ¥ 707-895-3837.