Re: Phone line interface for DTMF
- From: Tim Wescott <tim@xxxxxxxxxxxxxxxx>
- Date: Fri, 22 Jun 2007 12:19:33 -0700
jmarc wrote:
Hi all,
I would use a 600 ohms phone line transformer
to have dc isolation, for transmitting DTMF from
a computer.
My very simple desing work at home, but
doesnt work at the office. It seams I don't
deliver enough audio level of DTMF.
Earlier, I bought a very simple "play/record"
device who did work (more audio DTMF level),
but humming soon happen with differents
configuration.... (not use transformer in)
It is probalby caused by different ground
voltage level, between computer and Telco gnd.
Is someone out there, can rely me to some pretty
schematics on the web, or have any suggest
to do it right?
jmarc...
The quickest answer, if you can find one, would be an 8 ohm to 600 ohm coupling transformer. This will be a better match to your computer audio.
Alternately, amplify the heck out of the computer audio before applying it to the the transformer -- this is less than ideal, but may be easier to find parts for.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
.
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