> How large is the transformer ?

A transformer is a very eledgant solution, technology notwithstanding.
You can get very small main transformers - certainly under 25mm^2 
footprint.
Jinx may be able to comment due to recent similar experience.

An alternative is a purpose build double tx, single rx opto made for 
this sort of task. There are a number available. The sender uses a 
feedback loop to contioj the sending signal and the receiver slaves 
this. Opto tx drift not a problem.

Infineon HCNR200, HCNR201
"High-Linearity Analog Optocouplers"
0.01% non linearity
The light side of the force at work.

Clare AN107 Linear Opto Couplers (Google knows)
LOC110. LOC111. LOC112
Techniques apply to other manufacturer's products.

I have often thought that you could probably do an OK version of this 
using a std dual opto IC.
Run both TX diodes in series and replicate techniques above.


        RM 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist