I found an old rotary phone on a flea market and decided toplug it in. My land line goes through the cable modem, which doesn't support this old way of entering the phone number. What I need todo is convert the pulses of the phone to dual tone multi frequency tones. Step one is to reverse engineer the old phone interface. I connected a scope to the connected phone plug and got these signals:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIopa4DRIO6EwiIrDEFokFzLLwDMdQ6AX71FVDtvUtrkuVsLKNwGGVisly6HvFEDn2686tO9ErIwiFWcxs8Ugo0E_oU0eUxiO0L9e2qDXNEoB2GJ5gFLpxSJE5QtWSBcT_cqhkB2DNznO_/s400/2015-12-28+21.18.12.jpg) |
On hook. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3tUX48Owrq2BfH6yd8zMSOpmoAjLQjWDKAupP0Wxeqp1Jsj0P8vrH2KfFD3GSL4p000jvuvtcAZhOxzj86XRcLtmswmP8zKf6kIs7AVD2I58huXTCr3_ox7-WWdRKEnsTvqYb10kawAse/s400/2015-12-28+21.39.07.jpg) |
Off hook, with speach. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgm7GrAOaxeMkMzBzCq_NlTa59LXWJSCMiphH1gas_ARI_bg6HFMnpY-59HMaHXxDkCttSdzJMWh4DmzLa8eHBPTkeUjWiJGmTBI_Q-b_zHVhkLrxD3Qu4uJLC6uQg7gPJqyCqeH3bsj_oB/s400/2015-12-28+21.25.11.jpg) |
Receiving ringing. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizBHDSwUp2yrGlv77YLNFr3H2aZNN14RQ6t-1afNzw2Y3dG_9xtIO0D1N2Zr3uNyudSf3QkiXcvLeziDKYF5qyP5XWdpRz5kls_kXhfEk6_IJtvlm81YfN2MdRWG1SYxTV9fAXNGhXnWUJ/s400/2015-12-28+21.20.24.jpg) |
Dialling a "4". |
My initial thoughts is to connect these signals to a microcontroller to count pulses, and then let the microcontroller inject the right dialling tones on the line. First thing to do is to solder phone plug connectors to a perfboard to see if I can convert the 48V signals to logic levels (3.3V on 5V tolerant ports is my thought).