Phone digital answering machine

Posted on Sep 12, 2012

This unit is an upgrade of the previous phone call interceptor. Instead of using an answering machine to provide the outgoing message and recording functions, it uses the ISD4004 (from Windbond Electronics). The ISD4004 records up to 8 minutes of audio. I use the first several seconds for outgoing message prompts. The remaining time is used to record up to 30 messages, depending on message length

Phone digital answering machine
Click here to download the full size of the above Circuit.

When a call comes in it prompts the caller to enter the access code or to hit '0' to leave a message. If the proper code is entered, the device 'rings' an external speaker and waits for a phone to be picked up. If the phone is not picked up after several rings, it says 'good bye' and hangs up the line. The caller can hit '0' at any time to leave a message. The message time is limited to 40 seconds. Any of several phone extentions plugged into this device can be used to retrieve messages. The messages are played out thru any phone. They can also be accessed remotely by calling in and entering the 'secret' access code. For now, I am just providing the schematic and source file for this project. Later, I hope to elaborate on the details of the design.

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