Nectarine
Infamous OneLiner
Agemixer
(02:55:17)
for tad more complexity, there could be a latch chip for inputs and outputs for digital signals buffered, but also some kind of output signal followers
Agemixer
(02:53:06)
..to give it some line-level power, could be just be a simple bc547 transistor biased to center, and both input and output with a capacitor.
Agemixer
(02:51:07)
always use capacitor in input and output lines of analog signal, you might also need a resistor (attenuator) for the final "line out" signal, could be resistor + trimmer/potentiometer of some lowish R value, so you might need a little preamp anyway
Agemixer
(02:46:44)
then the driver code only needs to check, WHEN your ADC converter reached the level of the reference triangle signal (sample).
Agemixer
(02:41:57)
..."which signal is higher": the (+) input drives the opamp output up to 5v, and (-) input pin drives it down to 0v.
Agemixer
(02:40:20)
wire that result back to some PC or C64 port's input line, so that can notice when this input is toggled, then this triangle signal sample sent to the port is the actual sample value reached the same value 
OPAMP just does the comparison
Agemixer
(02:35:11)
the output of this opamp gives the result, at "exactly at time" the value rised higher compared to o reference signal, giving out 0;or 5volts, "0" or "1" bit.
Agemixer
(02:32:24)
add a simple OPAMP chip to your card board. Give the (+) pin the audio input signal and the "(-)" pin this reference signal.
Agemixer
(02:29:34)
a very simple ADC converter: you can make this DAC, then manually drive it a triangle waveform, starting from 0 and adding up to value 15, fast. this gives a reference signal.
Agemixer
(02:27:04)
so that 0000 gives out 0 volts, 1000 (=8) gives out 2,5 volts and 1111 (=15) gives out that almost 5 volts.
