From: Ian Charnas (icc@po.cwru.edu)
Date: Fri Jul 05 2002 - 00:18:02 EDT
> Could anybody having enough knowledge on electronic circuits send me a
circuit
> diagram so that i can connect my phone line to the line-in of my sound
card? If
> i can do this, i would be very glad and continue to try to code the dsp
stuff.
Yes -
http://www.iancharnas.com/docs/projects/telephone-recorder/telephone-circuit
.gif
The capacitor is there to block the DC (voice comes through on AC). The
600:600 transformer is the most important piece, it provides electrical
isolation between the telephone and your sound card. The zener diodes are
there to protect your sound card from the high voltages seen when your phone
rings. All these pieces can be bought at radio shack, or any decent
electronics store.
A few notes:
1. Do *NOT* use one of the shoddy Radio Shack telephone recorders. First of
all they do not provide electrical isolation between your sound card and
your telephone line (no transformer, only diodes and resistors), and second
of all the impedence is not matched to your sound card and you will get a
ridiculously loud hum, which would make your project that much tougher.
2. Do *NOT* merely use a transformer. As your telephone starts to ring,
the high voltage generated in the secondary winding will kill your A/D
device (sound card?).
Hope this helps
-Ian Charnas
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