Hi,
Understood. The code I have written for the arduino takes the pulses and converts them into tones. Basically if I detect 4 pulse counts on the pin, I send out the tone for 4 using the tone library. This i have managed to get working enough to convince playing down an open line to dial 1471 (a nice handy test number). Debound has also been considered in this matter.
The reason for doing this was that I destroyed the tracks for the numbers on the cordless phone I was using. Therefore I was going to play the sounds down the line when dialing to save distroying another phone (which i seems I have to do anyway, but thats another story).
So my problem was how to tie in the two microphones. I think the simplest is to leave the existing microphone and have a small (earphone) speaker glued beside it and insulated for noise so that we have a dedicated mic for hearing dial tones. Although, later I will be investigating an audio transformer to do this job for me so I can tie in the ardunio outputs direct to the mic port without this hack.
As I'm not auto dialing, I'm not needing to detect busy signals or other such like, as the user of the handset should be able to hear this.
Thanks for your post though! It gives food for thought if i'm going to move on with my other project ideas....