As with most precision equipment, microgram scales are usually very expensive. The close tolerance machining of sapphire pivots and computer control add to the cost. Not all of those components are necessary though. This article from Scientific American demonstrates how to build a simple microgram balance using a salvaged galvanometer. Once calibrated, the output voltage will have a direct linear relationship to the weight. There is a more recent version of this project that uses a microcontroller to overcome static friction and auto center.
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We’ve posted our How-To for the week over at Engadget. Do you have an old modem lying around? Have you been dying to record some of your phone conversations for those podcasts or homebrewed movies or crazy flash animations you make? Wait no longer! Build yourself a little circuit to change the analog phone’s audio to regular line audio to record with your sound card. Remember that it is illegal in many places in the world to record phone conversations without both parties’ consent.
Continue reading “How-To Build A Telephone Recording Circuit From An Old Modem”