dtmf

Hello:) I'm working on this old touch-tone telephone (Statesman 9040R - see picture). I'm essentially building a new circuit from scratch - it won't be connected to the phone lines but will instead be an arduino based interactive playback circuit. I would still like to understand how the old...

Hi all, I'm currently reworking an old touch-tone telephone, which involves redesigning the circuit to avoid the whole telephone line high voltage AC circuitry etc. In my first prototype I got on fine using an IK semiconductor 91214b IC to do DTMF generation, with the keypad keys connected as...