Don't these all require a separately-derived power supply on the 
measurement side?

That would drive the price up...   Which is kinda why I'm thinking at 
this point that perhaps adding this as an "option" might be better.

Unless you have a suggestion for how to provide an appropriate power 
source on the measurement side....which would be inexpensive to implement.

-forrest

Apptech wrote:
>> What I had hoped was for some magic, inexpensive solution 
>> where I could
>> avoid issues with measuring everything in relation to 
>> ground, including
>> unexpected ground loops or similar.
> 
> Several that I have already mentioned can be very cheap.
> VCO or PWM to optical.
> PWM can be converted back to analog at output with filter.
> VCO can convert to analog with monostable.
> 
> Digikey shows  LTV84x quad optos down to under $US0.40 in 2k 
> quantity.
> 10 cents per opto.
> 
>         http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=LTV-847S-TA-ND
>         http://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTV-817_827_847(M,S,S_TA1).pdf
> 
> Use as PWM, VCO couplers OR in analog mode.
> 
> While there are no claims as to matching you MAY find these 
> are well enough matched per package to allow two sections to 
> be used in the analog feedback model used by fancy matched 
> parts. This WILL work at some accuracy with any optos. How 
> accurate depends on the parts.
> 
> 
> In digital modes a cost of under $US0.50/channel seems 
> possible. Maybe less.
> 
> 
> 
>         Russell
> 

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