TITLE
Apple III: Game Paddles

Article ID: 13
Created: 9/21/84
Modified: 7/27/98
 

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TOPIC 
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.



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DISCUSSION 

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