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3 transistor non-contact mains detector

Bluejets

Oct 5, 2014
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Saw this video the other day while stooging around looking for something completely different (which happens many times).

Many times see people looking for ways to detect when a device is powered up and to operate other low voltage or whatever equipment.

Seemed a brilliant idea to me at least....

 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Spot the obvious problem.

what limits led current?

Also... "Charge pump"?!
 

ramussons

Jun 10, 2014
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Purchased something like this more than 12 years ago from a local shop. It still works !!!
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Well, the whole idea is for adapting to a uC .......poo poo it if you like but I thought it was a good idea.
Why poo poo it? If it works, use it. These non-contact field sensors are all over the Internet and it sure ain't rocket science. The Arduino/RPi interface is rather obvious, too, to anyone "skilled in the art". The only "problem" I see is sensitivity: either too much or too little and no easy way to vary it, other than adjusting the "antenna" by making it longer or shorter or coiling it or whatever works for you.

If this is going to be used with an Arduino or RPi it is likely a fixed or semi-permanent installation, so there is plenty of opportunity to farkle with it until it works to your satisfaction. Please take the time to Google this circuit, especially the Jameco website which (unbeknownst to me until now) has a huge DIY hobbyist page or two or three... I have used Jameco to purchase components, but didn't realize there was sooo much more if I had only taken the time to look.

Who knows who "discovered" the original circuit (I recognized "hum" pickup on my phonograph as a child in the previous century by touching the input circuitry from the crystal phonograph cartridge with my finger. Never considered using this "information" to make a non-contact AC voltage sensor though!) but there have been "improvements" and even a patent issued, all based on CMOS integrated circuits instead of discrete transistors as shown in the video. There are extensive Asian copies available. Whatever floats your boat.

This circuit is a good way to gain practical experience with, and a "feeling" for, AC fields... which we are all immersed in 24/7/365 thanks to Nikola Tesla. Put the circuit together and use a cheap battery-powered LCD oscilloscope to explore the AC fields all around you. LED and audible sounder are optional.
 
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