Project Caller ID

Basically it is a DTMF decoder for your computer.

Electronics

Basic schematics : Basic design
The basic circuit works just fine, connect Q1..Q4 to Data0..Data3 on the parallelport, Ack (Pin 10, Interrupt) and ground, and you're up and running (and a +5V source of course).
You should however not connect the circuit to the parallel port before your code is running and has swicthed the data pins from output to input, else you might short circuit them.
That is the reason I made these minor changes : End design
First, all four output pins Q1 to Q4 are converted from totempole to Open Collector with four transistors and eight resistors.
Secondly, instead of using the datapins, I reconfigure it to use the four open collector control lines.
A short circuit is no longer possible.
Here is proof : A foto

Software

For Linux, must run as root because of ioperm : callerid.c

Misc

My notes from the project : notes.txt
Tech notes on caller ID : DTMF_techinfo.txt