Re: Phone line interface for DTMF
- From: Robert Baer <robertbaer@xxxxxxxxxxxxx>
- Date: Sat, 23 Jun 2007 07:28:42 GMT
jmarc wrote:
Hi all,First, you cannot DC couple the transformer to the phone line, as Ma Bell uses 48V to detect on/off hook and other housekeeping chores.
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...
Second, here are at least two completely phone systems: "standard " MaBell and electronic types (Centrex, etc); they are not compatible with each other.
.
- References:
- Phone line interface for DTMF
- From: jmarc
- Phone line interface for DTMF
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