Hello nice people.
I'm trying to convert an old analog game system controller (Vectrex) to work on a PC through a gameport for a magazine article I'm writing. I need to create and document a circuit to do the job but it's getting a little over my head due to the oddball way the Vectrex controller is designed to operate.
The way it works is that it takes +/-5v input and outputs it between +/-3.5v for each axis depending on the value of the pots connected to the joystick (at least I think that's what's going on). Here is a schematic:
**broken link removed**
(VR-X and VR-Y are 10k pots). The schematics show R601 and R603 as 4.7k, but measuring them gives 3.5k. The pots at r602 and r604 are factory set at 4.2k.
So VR-X and VR-Y vary the voltage coming out of X and Y between +/-3.5v. I need to convert this to a ~0-100k range of resistance to match what a PC's gameport requires. I'm thinking of using some type of voltage controlled resistor to do the job.
As I see it through my electronically-newbish eyes, what I need to do is:
1) Figure out how to create both -5v and +5v from a single +5v source (a PC gameport's +5v pins).
2) Build or find a voltage controlled resistor circuit that will take an input range of +/-3.5v and convert it to 0-100k resistance across two points, following the input voltage linearly. -3.5v = 0k resistance, 0v = 50k resistance, +3.5v = 100k resistance.
I need to avoid modifying the original Vectrex controller's circuit so that I don't anger Vectrex collectors/preservationists.
For the voltage controlled resistor, I was looking at the DS1666-100 as an option.
**broken link removed**
It looks like it has most of the things I need except I'm not sure the inputs are quite what I need. Any opinions on that or other alternatives?
Any advice for either of my two objectives for this project would be appreciated.
Or, if you have any ideas about how to do it a simpler way, that'd be great, too.
I'd be happy to credit anyone who is able to help in the magazine article if they like (it'll be published in the February issue of Hardcore Gamer Magazine -- deadline's coming up quick, too!!).