On Thu, 10 May 2007 11:50:08 -0700 (PDT), you wrote:

>Well, I've been trying to solve a particular problem for a few months, sorta on again, off again issues.
>   
>  Simply put, I need to know when something has been unplugged from a AC socket.  I don't care about how much current its drawing (I do...but I dont need to know), because in some cases it might be a 100mA wall wart and in other cases a 100W power supply.  I just want to know....did it get unplugged.
>   
>  I've looked at some exotic solutions like power monitor chips but they aren't really designed for this.  I've played with Allegro hall sensors but the sit at 2.5V nominal, and just mimic the AC waveform and yes, with a larger load I can see it but smaller devices do not make a large enoough effect even when I use a simple gain stage op-amp.

Look at GMR sensors - much more sensitive than Hall Effect.

http://www.nve.com/

I've used these in a system which detected on/off when clamped on the outside of a mains cable - not
sure how well it would work down at lower currents but definitely way better than Hall effect

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