I needed a way to extract audio from a phone line for my DTMF decoder. I found a site full of examples on how to do it, and I built an interface that suited my needs:
RCA output, with a signal strong enough to be fed directly to an audio amplifier or line-in.
The interface can stay connected on the line at anytime (no problems with the ring signal), and does not take of the hook.
The interface must provide isolation from the line.
I discovered that it can also be used to inject audio in the line.
Build Accurate LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and reset function to make sure the readings are as accurate as possible ... [more]