There comes a time when you need a logic probe, and being an amateur electronics guy, the real hardware is just too expensive. This page describes how to build it youself for about 2 Euros, work not included. ;-)
It features 8 input channels and time accuracy in uS range. It it timestamp based, meaning that every time one of the pins change, AVR sends timestamp and state of pins to your PC. Unfortunately, due to slow UART transfers it cannot capture fast signals very well (default buffer only has space for 16 timestamps, tested with 115 kHz and it worked). For continuous data capture it can only handle <3 kHz signals or so.
I probably missed something, sorry :-)
Don't forget to set your crystal clock in .c and .py files.