15.004 How can I make a PC-to-Apple Joystick converter?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
15.004 How can I make a PC-to-Apple Joystick converter?
If you are looking for the best stick at the best price for your Apple II,
building a simple PC-to-Apple2 joystick converter is the way to go. Practically
every computer stuff store carries PC sticks and you will have a wide selection
of brands and models from which to choose.
Note: The converter detailed here will not work with "auto-fire" circuits
included in some PC joysticks. If you use an auto-fire stick with this
converter, "auto-fire" should be switched Off.
For a modified design which supports both auto-fire and non auto-fire operation
see FAQs Resource R030PCA2RF.GIF.
My PC stick is a standard CH Products "FlightStick". A resistance
measurement produced a disconcerting revelation: the X and Y pots top-out
around 100k Ohms-- 50k less than a standard Apple II stick! Fortunately, you
can compensate for the difference just fine by adding a bit of capacitance. The
finished converter is shown below:
To PC Stick To Apple II Or to 16-pin IC plug
15-pin Dsub 9-pin Dsub ribbon cable to
female connector male connector internal Game socket
[1] [4] and [5] ----------[2] +5V [ 1]
[2] ----------------------[7] Button 0 (PB0) [ 2]
[3] ----------------------[5] X-axis (PDL0) [ 6]
[6] ----------------------[8] Y-axis (PDL1) [10]
[7] ----------------------[1] Button 1 (PB1) [ 3]
[3] Ground [ 8]
On the Apple II side ... 9-Pin 16-Pin
add 680 Ohm resistor between [7] & [3] [ 2] & [ 8]
add 680 Ohm resistor between [1] & [3] [ 3] & [ 8]
add .01 uF cap* between [5] & [3] [ 6] & [ 8]
Optional: for fine-tuning,
add a 500k trim pot
in series with the cap.
add .01 uF cap* between [8] & [3] [10] & [ 8]
Optional: for fine-tuning,
add a 500k trim pot
in series with the cap.
*Note: The Capacitors compensate for smaller R range of PC sticks.
The C values are approximate. There is some variation in the
built-in capacitance for each Apple II and a ".01 uF" cap may be
off by 20% or more.
For standard 100k Ohm PC sticks, picking a ".01 uF" cap pretty
well guarantees you will be able to cover the full Apple II
X and Y range (0-255). To make sure and to get a wide active
swing, it's a good idea to use clips to attach caps and check
performance using the program below.
A pictorial 'diagram' of this converter is available. For the
pictorial, see FAQs Resource R029PCA2XRF.GIF.
For checking and adjusting stick performance on your Apple II, use a
program which continuously reads and displays X and Y stick values. The program
below does this and displays "B0" when Button 0 is pushed and "B1" when Button
1 is pushed. Do a CTRL-C to exit.
20 PRINT "X= "; PDL(0); TAB(15); "Y= ";PDL(1); TAB(30);
30 IF PEEK(49249)>127 THEN PRINT " B0";
40 IF PEEK(49250)>127 THEN PRINT " B1";
50 PRINT: GOTO 20
Note: If your Apple II uses an accelerator chip or board, make sure that it
"slows down" for joystick accesses or just set Speed to "Normal" (1MHz).
Most likely, after X and Y centering is set (around 128) you will find
that the a stick tops-out too early in the X-max and/or Y-max direction. For
best control precision, what you want is for extreme values to occur near the
extremes of stick movement:
X (horizontal) Left= 0 Right= 255
Y (vertical) Up= 0 Down= 255
This way, you have lots of active swing which makes graphics work and playing
most games much easier.
If you included the trim pots in your converter, adjusting for maximum
active swing will be easy so long as you can get to the max 255 values with the
pots at lowest resistance. (Increasing the resistance acts like lowering the
value of the connected capacitor.) If your converter does not include the trim
pots, experiment with swapping in capacitance values between .002 uF and .01 uF
to get the best control 'spread'.
The converter I built fit inside heat-shrink tubing. Putting it in a small
plastic box may be better. You could mount the trim pots (and/or switches with
fixed "trim resistors") and select between settings for a 'Fast', short swing,
'hot' Game Stick and a 'Normal', full swing, 'cool' Game/Graphics Stick.
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