Great project! Good hustle with the multiple attempts...
I smile at the use of a 555 as an interrupt timer... I did the same thing in my 8088 senior project in 1996... Typically one wants the interrupts to be accurate and periodic (hence hardware dividers to adjust the rate), but the 555 is (typically) based on RC time constants and as such is subject to heat changes :)
So your operating system runs differently at different times of the day :)
Also, mine had potentiometers to control the two external interrupts (556), so you could change the interrupt rate in hardware and there was plenty of pot noise which was easily detectable in the output audio stream... tee hee memories.
I smile at the use of a 555 as an interrupt timer... I did the same thing in my 8088 senior project in 1996... Typically one wants the interrupts to be accurate and periodic (hence hardware dividers to adjust the rate), but the 555 is (typically) based on RC time constants and as such is subject to heat changes :)
So your operating system runs differently at different times of the day :)
Also, mine had potentiometers to control the two external interrupts (556), so you could change the interrupt rate in hardware and there was plenty of pot noise which was easily detectable in the output audio stream... tee hee memories.