I was reading some of Geo John’s projects and came across a crystal radio set that he built using two tuned coils. A crystal radio set refers to the type of detector used, which was once a galena crystal and a ‘catwhisker’ to find a sensitive spot on the crystal. Nowadays, that is no longer
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A few years ago the Joule Thief fans and others built many projects with a very popular toroid core that was sold from Electronic Goldmine, a surplus electronics company, for the affordable price of five for a dollar. Eventually the supply was all sold and it was no longer available. The stock # was G6683.
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Long ago I built DC-DC converters using a toroid made with tape wound core. The cores were about 2 inches O.D. and we used regular 12 AWG solid insulated house wire for the primary windings. Even so, these cores vibrated a lot at several hundred Hz, making a screeching noise. I saw some very small
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I’ve built an FM microphone bug or transmitter before, but it’s been a very long time since I wound coils for one. Long ago I would wind too many turns on the coil and try it out. The usual outcome was the bug would be transmitting somewhere in the low TV channels 5 or 6,
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I bought some cat# TOR-74 from All Electronics for 4 for $1.00. They say these toroid cores are Magnetics ZF410057C, but Google didn’t turn up any data on them. They are coated Grey, and are 9.5mm O.D., 4.5mm I.D., and 5.0mm high, or .375 inch O.D., .178 inch I.D., and .197 inch high. This is
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A long time ago, probably 200 years, the scientists experimented with electromagnets by winding copper wire onto a bar or rod of steel. Most anyone that is taking a physics class has been introduced to this electromagnet. This works ok for a battery or direct current but when the current is alternating the solid steel
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A lady at work brought in a solar garden light for me to look at. The problem was that it wasn’t working. It consisted of a string of LEDs, all colored orange, just like a Xmas tree light string. On the end was a small box that fit in the palm of my hand. The
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I found these Fair-Rite toroid cores on eBay for $3.49 (U.S.) and $2.07 shipping. The quantity is eight, so it works out to about 70 cents apiece. This is nowhere as cheap as Mouser, but for a small quantity it seems like a fair price. These should make adequate Joule Thief cores with about 12
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When the winding gets tough, double up the number of toroid cores, I say. This JT uses toroid cores that are less than 1/4 inch (6.4mm) outside diameter. The wire has to be fine to get several inches wound on a core. So I wound one core with the wire, and then coupled it to
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In 2009 we decommissioned the old PBX system after replacing it with a Cisco VOIP phone system. Most of our campuses just got rid of the equipment lock, stock and barrel, but the whole room full remained at my campus. Over the years, I retrieved a few of the boards, each one about 16 inches
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