Apple III: Game Paddles

Apple III: Game Paddles

Standard Apple II 150K game paddles cannot be used with the Apple III. A high impedance potentiometer like the Apple II paddle will not work properly connected to an Apple III port.
The analog inputs on Port A and Port B of the Apple III are designed to read a voltage between 0 and 2.4 volts and convert it to a number between 0 and 255. The schematic on page 82 of the Apple III Owner's Guide is drawn for a joystick with 5,000 ohm potentiometers.  Only the bottom 20% of the potentiometer's range is used. Using the +12 volt power supply will result in the most stable readings.

The following circuit can be used if the entire range of the potentiometer is desired.

            +12 or +5 volts
                       |
                       |
                       <
                       <  Rs
                       <
                       |
                       | <------ must be 2.4 volts at this point.
                       |
                       <
GC input ---><   Rp  (1 - 2K ohms)
                       <
                       |
                       |
0 volts  ____|

The voltage range at the GC inputs should go from 0v to 2.4v. The value of Rs can be calculated for +5 volt systems with this formula:

Rs = Rp * 2.6 / 2.4

For +12 volt systems use: Rs = Rp * 9.6 / 2.4

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