10 replies to this topic

[Great Hierophant]

Has anyone ever made a digital joystick for an Apple II?  Apple II joysticks work on the same principle as IBM PC joysticks except they use 150KOhm linear potentiometers instead of 100KOhm linear potiometers.  A Gravis Gamepad for the PC converts the directionals of a Gamepad into resistance values at the low, midpoint and high end of the resistance range.  I would suggest you could get a Gravis to work in an Apple II by changing the resistor packs from 47KOhm to 75KOhm and wiring in a 9-pin cable.  While not perfect for every game, there is a huge number of games for the Apple II that rely on simple "stick pushed/stick not pushed" controls.  Has anyone ever tried doing something like this?

[cybernesto]

I have. I built an adapter to use Atari style joysticks with the Apple II and it works great. Even though I have read this story about the 150k ohm necessary to cover the whole range, my Apple //c and other Apple IIe I tested required only 100k to reach 255.
https://123d.circuit...oystick-adapter
There are some other projects around with the same purpose but you won't find any as simple and with as few components as mine. The diagram only shows how to connect one button, which is what Atari joysticks have. But you could easily add a second one to use a Gravis or a Master System game pad.

[cybernesto]

Check this other project out to compare the complexity
http://www.atariarch...cc/chapter9.php

[cybernesto]

And another one
https://groups.googl...Mc/G5hbRUvrR6YJ

[Great Hierophant]

I have. I built an adapter to use Atari style joysticks with the Apple II and it works great. Even though I have read this story about the 150k ohm necessary to cover the whole range, my Apple //c and other Apple IIe I tested required only 100k to reach 255.
https://123d.circuit...oystick-adapter
There are some other projects around with the same purpose but you won't find any as simple and with as few components as mine. The diagram only shows how to connect one button, which is what Atari joysticks have. But you could easily add a second one to use a Gravis or a Master System game pad.

 

If your 100KOhm pots did the trick, a straight DA-15 to DE-9 adapter with the appropriate wiring may work sufficiently with an unmodified Gravis Gamepad.

[cybernesto]

You'll need the circuit anyway, but yeah, with the proper wiring it would work with the Gravis Gamepad.

[Great Hierophant]

The Gravis implements a version of this circuit : https://123d.circuit...oystick-adapter, so it may be worth trying "straight through"  At worst the values may be off.

[cybernesto]

Got it. Ok, I don't know the details about the Gravis but probably you will still need to invert the button levels. See this circuit instead http://apple2.org.za.../R030PCA2RF.GIF

[Osgeld]

I have wired a atari stick to my apple 2 and it works fine for games with digital type inputs 

 

to get around the 100 vs 150K pot issue all you have to do is add some capacitance tween the center pin of the pot and ground, This effectively sets the new capacitance in parallel with the one inside the computer on that axis, that changes the R-C timing ratio of the 555 timer responsible for that axis

 

to find the capacitance you need to use:

((original_potentiometer_value * internal_timing_capacitor) / new_potentiometer_value) – internal_timing_capacitor

 

using this formula you can use joysticks of any resistance,or in this case we know the original is 150k the new is 100k and the internal capacitor of the II is 22nF sooooo

 

((150,000 * 0.022) / 100,000) - 0.022 = 11nf 

 

10 is close enough and a extremely common value (cap code 103) by the time you account for tolerance it should be just about bang on

 

The more you know (its about the 3rd time posting this book on this site, eventually everyone will know lol) and yes this will work on other computers that use 555 timer based joystick interfaces like the IBM PC if you want to wire up some 10k thumbsticks out of a old playstation controller or whatnot

[MarkO]

 

< SNIP >

 

  Apple II joysticks work on the same principle as IBM PC joysticks except they use 150KOhm linear potentiometers instead of 100KOhm linear potiometers. 

 

>> BIG SNIP >>

 

Don't You Mean, "IBM PC joysticks work on the same principle as the Apple II joysticks, except they use 100KOhm linear potentiometers instead of 150KOhm linear potentiometers"??

 

I mean the Apple ][ was developed before the IBM PC....

 

MarkO

[Great Hierophant]

 

Don't You Mean, "IBM PC joysticks work on the same principle as the Apple II joysticks, except they use 100KOhm linear potentiometers instead of 150KOhm linear potentiometers"??

 

I mean the Apple ][ was developed before the IBM PC....

 

MarkO

 

That is an historical improvement, but even better is :

 

"IBM PC joysticks work on the same principle as the Apple II joysticks, except IBM PC-compatible joysticks use 100KOhm linear potentiometers instead of 150KOhm linear potentiometers used by Apple II-compatible joysticks".  The extra words make it clear which type of potentiometer is used by each type of joystick.  

Edited by Great Hierophant, Mon May 16, 2016 9:39 AM.