Microsoft-Paul Allen

[Fred Cisin]

>> Similarly, although they sold a joystick board, they didn't sell
>> joysticks.  DA15 connector for two joysticks.
>> In some of the documentation, the sketch of a joystick was clearly the
>> Radio Shack Coco joystick (which needed a different connector)

On Sat, 20 Oct 2018, Tony Duell wrote:
> And is electrically different.
> The CoCo Joystick is a potential divider across the 5V rail. Moving the
> joystick varies the output voltage (2 voltages per joystick, X and Y). This
> is fed into a 6 bit ADC (actually a 6 bit DAC, a comparator and some
> firmware).
> The IBM PC Joystick (like the Apple ][ ones) is a pair of variable
> resistors. This are the timing resistors in monostable circuits, acutally
> an NE558 chip (Think of it as being 4 555 timers always connected as
> monostables in one package). The software triggers the monostables
> then sees how long they take to flip back again.

Could you provide some remedial tutoring on what I am misunderstanding?

All of that circuitry is in the "controller".
The joystick itself consists of pushbuttons and two potentiometers.  NO 
other active circuitry.
Moving the joystick does not itself vary the output voltage, when it is 
not so connected.  Moving the joystick varies the wiper position along a 
resistive element.   (admittedly, if the ends of the resistive element are 
connected to voltage and ground, then the wiper connection provides 
a variable output voltage)

If the resistance is compatible, then what modifications need to be made 
to convert a "voltage divider" potentiometer to a "rheostat"/"variable 
resistor"? 
(wire to wiper and one end of the resistive element (already present), 
disconnect the connection at the other end of the resistive element)

YES, it was "intended" to be used differently.

If one KNOWS that it is impossible to make it work, then it makes it more 
difficult.


Could one safely ignore the "No user serviceable components inside" 
sticker on the bottom of the joystick?  :-)
And, of course, there is the difficulty of locating a DA-15 connector!
There are some on eBay, but the seller says that they are DB-15  :-)

--
Grumpy Ol' Fred     		cisin at xenosoft.com