Date   : Mon, 14 Mar 2005 21:34:07 +0000
From   : Joe N <ng22311@...>
Subject: Re: BBC analogue joysticks for PC

Thanks Richard, that was useful info, especially the shunt pots. I've 
been attempting to wire up an adaptor lead - with some but not complete 
success so far. I think I've hit on a far more (or perhaps less, 
depending how you look at it) fundamental problem. I'm trying to get the 
joysticks (both of them) working in such a way as to use them with 
BeebEm for Windows - or more precisely, Dogfight running under BeebEm 
:-). Anyway, I've gone back to basics and rigged up four mini 100k pots 
on a bit of breadboard to try to get my head round the problem a bit 
better. I've got it working fine and calibrated under Windows but I can 
only get one of them to work with BeebEm. Is it a feature of BeebEm that 
only one joystick is usable or does anyone have any suggestions as to 
how one might get two joysticks working with BeebEm?

Thanks,
Joe.

Richard Gellman wrote:

>
>
> Yup, its perfectly possible to do this, and in fact I did it with an 
> old joystick I got from Watford Electronics way back. Essentially, the 
> circuit design is identical: two "axes" consisting of a potentiometer 
> between 0v and +5V, with the variable output connected to the input 
> channel. The buttons then work as switches between +5V and the button 
> inputs.
>
> Here's the catch: Same circuit, different pinout. If you plug a BBC 
> joystick into a PC, it wont work. It won't fry anything either, but 
> you won't get any movement. For reasons which I assume are pure 
> coincidence (the BBC ananlogue port was pinned just before the Game 
> port was pinned for the PC) the two sockets use totally different 
> pinouts, but require no "interpretation" circuitry.
>
> So what you need, is one female 15-pin D, one male 15-pin D, some 
> wire, a soldering iron, and pin diagrams of both connectors. Then you 
> should be able to assemble an adapter that connects any BBC joystick 
> to a PC.
>
> Caveats:
>
> The PC Game port has TWO joystick connections on it, thus making a 
> total of FOUR axes, and FOUR buttons. On the BBC analogue port, there 
> are similiar circumstances, 4 analgoue in lines, but only the two fire 
> button inputs. How you wire these is entirely dependent on what you 
> plan to connect, in terms of exotic hardware. All two-axis two-button 
> joysticks will work fine if you split the PC game port into two and do 
> a straight conversion. If however, you want to connect something with 
> four axes, you'll need to sacrifice one PC game port for the two 
> surplus axes.
>
> The voltage levels between the PC and the BBC do vary somewhat. While 
> Windows' game device calibration should take care of this, you find it 
> well worth shunting a control potentiometer either in series or 
> parallel with the axis potentiometer (depending on desired control 
> type) to adjust how the axis is interpreted.
>
> Have fun :)
>
> -- Richard
>
> Joe N wrote:
>
>> Does anyone know if it is possible to make a hardware interface 
>> between original BBC joysticks and a PC? I remember seeing a curcuit 
>> diagram for a similar such thing for Amiga joysticks on a website 
>> somewhere, but wondered if anyone had any ideas about the BBC?
>>
>> Thanks,
>> Joe.
>>
>>
>  
>