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 Previous: W1AW Levitates 120-foot Tower |  Next: First Looks:SGC SG-2020 Transceiver |
September 1, 1998
Ted, K4MKX, recently dissected 9-V batteries and checks in with this interesting tip: Recently, after building a single-IC keyer, I needed a tiny 3-V battery. I thought I might be able to use two of the small cells from a 9-V transistor radio battery for this project. I was familiar with the insides of the old carbon-zinc type batteries, but for this project, I selected an alkaline battery.
I was in for a shock (well, not literally) when I opened the case. Inside were six tiny cylindrical cells, each in its own plastic sleeve, looking like smaller versions of a AAA cell. In this particular battery, the six independent cells were series-connected by the printed foil on paper end pieces held in contact with a thick rubber pad and assembly pressure. I checked one of the cells with a voltmeter and was surprised to discover that the case was the positive terminal while the tiny center conductor protrusion was the negative terminal! If you examine larger alkaline cells (AAA, AA, C, and D), you will see they're all constructed this way, although it doesn't look like it from the outside.
To make my 3-V battery, I needed to connect two cells in series and attach external leads. The center post (negative) easily takes solder after scraping it clean. The case (positive) will take solder, but only with some "persuasion," so I inserted a small, sharp safety pin between the case and the plastic sleeve to stretch the plastic. Then I slipped a bare wire beside the pin to make the connection. Removing the pin captures the wire. Voila!
I use a glue gun to hold the cells together to form a battery. Lay the cells together and run a bead of glue to do the job. The resulting battery is quite small and can be used in lots of tight spots. I sometimes use the glue gun to fasten the battery to the project circuit board or case as well. The glue unsticks easily when you need to replace the battery.
Subsequent investigation of different types of 9-V alkaline batteries revealed a second type of construction, where the six insulated sub-AAA cells are connected with metal foil strips spot welded to the terminals (similar to the way some NiCd packs are made. The entire assembly is shrink-wrapped in a plastic sleeve. For me, this is the type of battery to use, as one can easily solder to the foil strips. In terms of specific brands, the Duracell and CVS drug store brand are of the latter type. Radio Shack and Eveready are of the former (loose cell) type.--Edward B. "Ted" Beach, K4MKX,5112 Williamsburg Blvd, Arlington, VA 22207; e-mail K4MKX@hotmail.com
Michael, N4TMI, has a quick fix for anyone trying to get more volume out of a Radio Shack 21-543 DSP box: The cure is simple. The gain of the audio amplifier can be doubled by soldering wire jumpers across R54 and R57. These are clearly labeled 100-ohm chip resistors on the underside of the circuit board. According to the manufacturer's data sheet, the KIA7227CP audio amp chip does not require these components. Their only purpose is to reduce gain, apparently a bad idea in this situation. After the mod, it's much easier to get room-filling volume from a speaker. Sound quality is excellent, and digital signal processing is unaffected.--Michael A. Covington, N4TMI, 285 St George Drive, Athens, GA 30606; e-mail mc@ai.uga.edu
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