Pixel Form the creator of the Modified TI99 (Pixel Maelstrom) computer contacted me and graciously shared a few hints about his marvelous modified devices just to clarify my initial assumptions about their operation. So far there has only been 2 modified TI99s, both sold on Ebay. First one utilized SK-1 circuitry with datalines patched to TI99’s dual video chips. Ofcourse the right combination of patches would have to exhist given that the user has patched version of an SK-1 or any other keyboard.
His second version utilized a a somewhat different approach. In this case, audio was split into 3 streams with the help of High Pass, Band Pass, and Low Pass filter circuitry. The signals were then further processed by comparators with individual threshhold controls. The result was a binary 3 digit stream of data. Genius! This data stream drove a transistor array electronically switching various pins on the video chips.
Pixel Form is not about to stop experimenting given the amount of success, future plans include Microcontroller inplementation as well as video bending of other platforms including an Atari 2600 Jp.
Kudos and thanks for sharing. Will definatelly keep one eye on eBay and another on his site.