"Line in use light"

Hi, I hope I'm not posting to the wrong group.

I have a pretty standard touchtone desk phone and want to install a small LED light the would come on whenever anyone is on one of the other phones in the house.

What resources are there available so I can do this on the cheap??

Please respond by email if necessary.


Thanks, Bill Johnson

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Bill Johnson
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It's OK, but sci.electronics.design might be a little better - cross-posted and followups set.

There are several circuits to do this at

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Matt Roberds

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Dave M
MasonDG44 at comcast dot net  (Just subsitute the appropriate characters in 
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The good thing about this circuit is that it flashes, so it draws attenion to the LED. The bad thing about it is that it uses a CMOS part, which is susceptible to being zapped by lightning. It should have a .02uF bypass capacitor from pin5 to ground to reduce the possibility of a transient voltage spike zapping the chip. But it is still susceptible. So buy a few spare chips and use a socket, and when it gets zapped and quits working, just replace the chip. ;-)

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Watson A.Name - "Watt Sun, th

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