AVR-Chat

At 05:15 PM 8/12/2004, Graham Davies wrote:

>--- In AVR-Chat@yahoogroups.com, Dave VanHorn <dvanhorn@d...> wrote:
>
>> ... dual-optoisolator, and an opamp,
>> to implement a modem hybrid without
>> any transformer ...
>
>What happened to the DC wetting current of the line?  Was that 
>carried over the isolation barrier to?  Was the op-amp circuit line-
>powered? What bit rate or modem standard did this work with?

212a, we put the loop current through another circuit, a constant current ckt so it had nearly infinite impedance.

>I worked on this kind of stuff too. To avoid the non-linearity of wet 
>transformers I picked off the wetting current in an active circuit 
>and AC-coupled to a dry transformer. Expensive! Now, years later, I'm 
>working on SONET. 622 Mbit/s. Hey, that's optically isolated too!

Sounds like fun!