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Obtaining 1 Sec Clock Pulse From Power Line

okasional

May 14, 2017
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Unless you're age 70 or over you probably don't remember the golden age of digital integrated circuits when manufacturers like GE, National Semiconductor, Fairchild, RCA, Texas Instruments, Linear Technology, Harris Semiconductor, and many others all published books filled with specifications on all their products, application information, and virtually anything you could want to know about their products. When I moved a year ago I foolishly destroyed my collection of these wonderful old catalogs. The ability to quickly grab a data sheet online won out over shelves of outdated books. Recently I had reason to regret having done that.

I remember a circuit in either a data sheet or application note that showed I believe a multi-stage binary counter (perhaps a CD4024) and a quad gate that decoded the count of 60 to recycle the counter. Feed the counter's clock with 60Hz and get a 1Hz output. That was when I first learned safety was not a problem with this line operated circuit because all you had to do for the CMOS input was connect a 1 megohm or larger resistor to either side of the AC line. You can probe around inside a wall socket all day with a 1 megohn resistor and never feel anything. This is not a rocket science problem, and I could probably figure it all out. But I have fond memories of the data book page that showed that circuit, and if anyone has the book I would be ever grateful to obtain a copy of that one page. If I had to guess, I'd say it might be in an RCA CMOS IC data book. In case you didn't know, you can freely download a PDF file of the entire 1983 issue of that book on the web, but I couldn't find it in there.
 

Audioguru

Sep 24, 2016
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You must filter the power line because it is full of hash from light dimmers and high current things turning on and off. The counter will count all the hash.
I bought clock radios that have a backup battery for $1.75 each at a surplus store. They sound awful but the clocks work well.
 

okasional

May 14, 2017
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May 14, 2017
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Audioguru. good point. I'll be sure to filter the input.

Harald, Thanks. I had the CMOS book but not the Linear book, and was glad to get it.
 
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