As I don't have an oscilloscope yet so I needed a cheap way to analyze some signals, I decided to build a simple logic analyzer to use with PC's parallel port. I used the schematic from here as a base and made my own improvements to it so it would work better. I added a 100 ohm series resistor and a 10k ohm pull-down resistor to every line and I take the power from a +5V regulated supply. No PCB available yet because it is so simple that I built it on a dot coppered prototyping board.
The device works quite well and I'm using it with my old 300 MHz laptop, which is running Debian Unstable with Fluxbox. The software I'm using is The Fabulous Logic Analyzer. So far it has worked great and I managed to get all the timings right from my own servo controller (it is debugged in the photos below).
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