Re: Commodore joystick ports

From: Scott McDonnell (
Date: 2004-10-23 01:02:39

----- Original Message ----- 
From: "Jim Brain" <>
To: <>
Sent: Friday, October 22, 2004 5:12 PM
Subject: Re: Commodore joystick ports

> Scott McDonnell wrote:
> >Jim,
> >
> >As Hársfalvi mentioned, it is current that needs to be generated, not
> >voltage. A resistor creates a voltage drop across it, which is a function
> >current. (Resistance=Current/Voltage) The voltage is 5V, the resitance is
> >range that you know from the potentiometer values, you simply need to
> >the corresponding current to emulate the resistance you need.
> >
> >
> The nitpicker in me always thought it was V=IR, so R=V/I...

You are correct. I was having a mild flatuation of the brain... :)

> I looked at a resistor ladder DAC, but I don't have 16 IO pins to spare
> (8 per POT), and the board real estate for 2 ladder DACs puts me way
> over the .625x.625" pcb space I have to work with. (On a related note,
> anyone have a source for a bit larger DE9 shells?)
> >in 256 different currents at each axis input. Probably way more
> >than a commodore mouse provides.
> >
> >
> Oh, I don't know.. If someone wanted to re-use this as a 1351 mouse
> emulator, they'd need either a stable 7 bit resolution (1351 discards
> low bit due to timing issues), or 8 bit resolution.
> I'd travel down the path, but as of last night, the idea used by the
> 1351 designers and Hársfalvi noted in his project is working pretty
> well.  I can get from 10 to 255 on the POT lines using 2 10K resistors,
> configured as noted in his PIC mouse project plans, and the jitter is <
> +-3 (I cleaned up my code to reduce execution times), and only uses 3
> pins on the AVR (INT1 and 2 data pins).

Ok. Sounds like you got it working satisfactorily. : ) Just thought I would
pipe in and offer my own suggestions. Hope I was at least some help.


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