The answering machine is a device used for recording telephone conversations as well as automatic answering device. The voice recording machine is a paradigm of a telephone answering machine. Basically, the system has a recording circuit which store all the messages in ISD9000, and a control circuit which is used to select the messages.
ISD1900 ChipCorder series is a single chip multiple message record/playback device with dual operating modes (address and Direct mode) and sampling frequency 4 to 12 KHZ. In this tutorial, two recorded messages are used. the first one holds the phone ringing and the second holds my voice.
The control circuit in this project is represented by ULN2003 which is controlled by PIC micro-controller to select the messages according to the received signal from the switches. BTW, I did not not test the circuit on real telephone because I do not have one!!! For this reason, I used two switches, one to make a call and the second to answer it. If there is a call, the phone start ringing, until there is an answer. If there is no answer, my recorded voice will appear “Hi, I’m not home now. Please, call me later”.