Here are instructions to turn such a tester into a not-so-precise analog display to monitor the CPU load on a Linux system, controlled by a serial port. You can build two variants of the display: - An AA Duracell battery with a tester. Energizer testers should work too, but I haven`t tried. I got a pack of Duracell Ultra M3 batteries, product code LR6-MN1500.
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Cleanly unwrap the tester off the AA battery. Be careful not to pull on any one side too hard, or you`ll warp it and it`ll be that much harder to connect on the breadboard. Personally, I lift both corners, gently unroll it on 3/4 mm, then use a knife and my thumb to finish taking it off the battery with an even pull. Here`s what it should look like, before trimming the warped bit of the packaging : Here`s the really hard bit : making a somewhat reliable connection between the tester`s conductive ink points and the rest of the circuitry. To do that, place the tester on the breadboard, near the upper edge, and mark out precisely the breadboard holes the wrapper`s white dots fall on. Spend some time aligning the right white dot (on the "minus" side), as the patch of conductive ink there is very thin and right on the edge of the tester. The dot on the left ("plus") side is less problematic. To make the connectors, solder bits of "hairy" copper wire (like that found on common mains electrical cords) in the holes you marked, and leave the "hairs" sticking out where the tester will be installed. They`ll help make a correct electrical contact with the tester`s conductive ink. Cut out a piece of clear plexiglas from the CD case, tape one edge to the upper edge of the breadboard, and punch a small hole near the bottom edge. This makes a window to hold the tester and press it flat against the breadboad and the connector. Solder the...
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