Software based Caller ID project- Problem with getting caller ID signal

Two of the line look like they will carry the signal that you're after, the ones that connect to the topr-right corner of the IC with the series resistor and capacitor, but you cannot/shouldn't connect them straight to you PC without:

  • knowing the expected signal levels of the signal you are interested in, the inputs must happily accept the signal levels;
  • protect the input against ring voltage, which can be up to several 100's volts peak to peak;
  • protect against overvoltage as a result of eg. lightning in the neighbourhood;
  • an insulation transformer for galvanic separation of the phone line/PC. (You can often find those in old modems or telephone sets.

It's an old thread but in case you are still working on this, or anyone else is interested, there are 2 examples of completed Software based PSTN Telephone Caller ID projects here: or Both use a software AFSK demodulator to interpret the CLIP information which is send with the ring burst and include a schematic diagram and all software. One also even handles spam calls.