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Analog RC unit as Digital Joystick for Commodore C64 C128 Amiga

Foreword:
Know the problem, old gaming computer found and working but got no Joystick, BUMMER !! cant wait 3 weeks to order one ?
Commodore 64 128 and Amiga uses the same connector and pinout for the Joystick ports, it is simply a switch to ground in each direction.
All sorts of analog potentiometer joysticks exists, RC units as shown here, playstation and PC joysticks are most often also analog.
Here is how to convert the analog resistor to a digital signal. So you can start playing allready tonight.

First test, prove the computer works, and all pins directions are ok, it actually was playable with this one.

The schematic is simple, you need 4 comparators, they works almost like an op-amp however they got opencollector output
so they pull to ground, and they COMPARE the two inputs +/-
The 100 ohm resistor set the dead-band in the centre position of the analog joystick,
if you want more travel before it activates, then change the resistor to 220 or even 470 ohm

Not many parts needed, easy to solder, here a very fast mock-up.

zoom of the ugly test mock-up. dont win any beuty contest, but it really works

The old RC unit is now a fine commodore joystick, added a fire button too.
the centre trimmers are used to make sure no signals are active when in perfect centre.

The best Commodore 64 game ever, Boulderdash all you need for many days of fun.

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Thomas Scherrer OZ2CPU 2017
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