[Asterisk-Users] Digium FXS modules too fragile?

[Andrew Kohlsmith]

On May 23, 2005 02:44 pm, Ian Pattison wrote:
> Yesterday, in an attempt to take back my phone room, I pulled everything
> apart as far back as the demarc and rebuilt it. In the process of putting
> things back together I accidentally connected my incoming lines to my FXS
> ports and my phones to my FXO ports. I quickly realized the mistake I made
> and corrected things but not before one of my FXS modules was smoked by
> incoming ring voltage.

Ouch.  I'm sorry.

> Has anyone else seen this? Also, wouldn't one assume that a module designed
> to generate an 89V ring tone could also accept it without being destroyed?

While it sounds like something that may be plausible, it's just not true.  
It's hard to protect against voltage you should be able to generate because 
the protection circuitry would kick in when YOU generated it too.  Speaking 
as an EE (but nondegreed, I've just been doing it for 10 years) you *can* 
design in tricks to work around these issues but they just jack up the cost 
on the device and this is already a cost-sensitive market.  I don't blame 
Digium for not including it at all.

Basically it's like saying your portable gas generator should be able to take 
having 120V applied to it since it can generate 120V.  It just doesn't work 
that way, I'm afraid.

-A.