[Matt] was looking into some software that allows him to use his audio card as a means to control analog audio devices. After seeing how it worked, he got an idea to try to do the opposite. He is sending a signal into his audio input, and piping it to a pice of MIDI software. The input he has chose is a foot switch. To create the signal, he simply needed to supply voltage while the switch was depressed. You can see above that he used a battery and a simple contact switch to send the signal. He then piped it to a virtual MIDI port using Maple Virtual MIDI Cable. Unfortunately, this isn’t suitable for knobs, but that may be next on his list.