Date   : Thu, 08 Nov 2007 16:05:06 +0000
From   : fragula@... (Fragula)
Subject: Joysticks

>
>
>     Is there any 'magic box' that would allow me to use my trusty old
>     voltmace joystick with a BBC emulator on a PC, or are the
>     technologies too far apart?
>

The technologies are very similar, but not the same, in spite of the
similar connector.

The primary difference is in the notional value of the potentiometers in
the joystick. On a Beeb this is nominally 10KOhm, but on a PC the
permitted current drain is lower, thus 100KOhm pots are used.

On a Beeb, the Voltmace sticks work rather well. I've yet to be
impressed with any analog-game-port connected stick on a PC. In face,
they have all sucked wholeheartedly.

The problem probably being that the RF interference over the "higher
impedance" circuit on the PC can overpower the lower current DC voltage
being measured. There may be some other factors too, but that one is enough.

I guess you could do something crazy like using a couple of dual gang
90K pots as"trim" controls, with each half in series with once side of
one pot of the Voltmace

So: (ASCII graphic isn't looking hopefull at the mo)

Circuit would be

PC game port v+ out to Left track of lower ganged trim pot

Wiper of trim pot to Left track of Voltmace pot

Wiper of voltmace pot to X or Y in on PC.

Right track of Voltmace pot to  wiper of Upper gang of trim pot.

Right track of upper trim pot to ground/0v of pc joystick.


Similar for Y axis. :-(
it could be done with op-amps, or photon coupled bilateral FETs, but
that's disproportional to the need.

Better to not bother, get a cheap chinese USB gamepad, and save the
voltmace for the beeb.

Cheers!

M.