[sci.electronics] Taking phone off hook with TTL signal

dougy@spam.ma30.bull.com (Doug Lethin) (06/12/91)

Hello

There has been much discussion in sci.electronics about line in use 
indicators recently.  

Another phone project that I would like to do involves taking a phone
off hook by using either a 0 or 5v signal.  I have not seen this in
the past two months so I bring it to the newsgroups attention.

My understanding is that I can just use a transistor, and connect
the source to the either tip or ring, and connect the drain to then
node where my phone would connect to the tip or ring, like a basic
switch.  When I want the phone to go off hook, I can just set the gat
voltage to 5v.  This will allow current to flow between source and drain.

Is there something I am missing here.  I know that this configuration will
work like a switch for ttl DC levels, but will it work for AC connections
like the phone.

Any insight is appreciated.  If there is a better way, or if the method 
mentioned will not work, please let me know.

Thanks

Doug
dougy@bubba.ma30.bull.com
--
 == Douglas O. Lethin                Bull HN Information Systems Inc. ==
 == 508-294-5904                     300 Concord Road   MA30 803A     ==
 == dougy@bubba.ma30.bull.com        Billerica, MA 01821              ==