Date   : Thu, 31 Mar 2005 17:33:31 +0000
From   : "W.Scholten" <whs@...>
Subject: Re: BBC analogue joysticks for PC

Richard Gellman wrote:

> Here's the catch: Same circuit, different pinout.

Absolutely *not*.

The PC uses a resistor measuring method. An inane design by IBM, which
is the reason one needs to calibrate joysticks there. All this was
probably just to save a proper AD IC (on a horrendously expensive
machine this makes no sense whatsoever). The method used eats up CPU
time as well.

Anyway, this means that the PC uses just 2 of the 3 lines coming from
any of the potentiometers that the BBC joysticks use (the BBC uses the
potentiometers as voltage dividers).

IIRC this should be no problem by using XY1 -> VREF or analogue ground,
X1/Y1 -> CH0/CH1 and leaving the other analogue ground or VREF
unconnected. And for the fire buttons, from the diagram 0V/PB0 -> ground
(for switch1)/switch 1. For some reason when I investigated this I just
rewired my BBC joystick for the PC connector (ca. 1998)

For more, see e.g.:
  http://www.epanorama.net/documents/joystick/pc_joystick.html

Regards,

Wouter
--
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