The heart of the circuit is a quad analog comparator that converts the analog signals from the KY-023 joystick module to open collector signals. 

The circuit is based on the LM339, a quad comparator with open collector outputs, so they can be directly connected to the ATARI port, at least two of them, because the other need to be inverted using bipolar transistors. 

The  negative input of the comparators are connected to a 3 resistor network that provides equally spaced thresholds around 1/2 of the Vcc. The center resistor is adjustable to provide a sensitivity adjust. As the comparators share the same voltage references, the sensitivity control actuates on both axis at the same time.

The basic circuit, as presented below , can be simulated online (link).


The PUSH button of the KY-023 analog module was used to provide a second action button on the other Paddle line available at pin 9. As this button is tied to ground it is necessary to use a PNP transistor to actuate the line.

To be continued....