I've used standard wall warts for this with success. 120v in, 12v AC out and 
it's 10:1 ratio to work from to get the high side V. Of course, any ratio would 
work, but the particulars depend on what you use on the PIC side. UL listed 
wall warts are cheap and available and just plug in.

-Skip


Forrest W Christian wrote:
> I have an application where I need to monitor voltage and current of 
> three phase power in datacenters .... typically in the US, we're talking 
> 120/208 Wye (120 each leg to ground , 208 leg to leg).  
> 
> The current is easy - three current transformers wired to an appropriate 
> circuit to rectify, filter, and measure...  pretty standard 
> engineering.   Plus, current transformers are available pretty cheaply.
> 
> Measuring voltage is a bit tougher in my mind.   I'd really like to keep 
> the AC voltage isolated from my circuits.   I have lots of ideas on how 
> to do this (build a second circuit, with a PIC which is interconnected 
> with the line voltage, and sends a serial datastream out a optocoupled 
> line, etc.), but all of them involve building something which attaches 
> directly to the AC line (which means the possible need for UL listing, 
> and the added dangers/liabilities of having a product which does so).
> 
> I guess I'm looking for a couple of things... first of all if there is 
> something commerically available that I've missed that will measure line 
> voltage and output it as some sort of isolated low voltage - similar to 
> a current transformer.   Cost is definitely an object.
> 
> Secondly, if there isn't an option that way, any design ideas which are 
> simple/effective for measuring this with a PIC would be useful.  Thanks.
> 
> -forrest
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